Direct observations of slow photo-induced structural and physical changes

Direct observations of slow photo-induced structural and physical changes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Direct observations of slow photo-induced structural and physical changes Toshio Naito, Minaho Nakaie, Kaito Murakami, Yuka Nishiyama, Shuji Shiose, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4811531/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Photoexcitation and the subsequent physical or chemical processes are often too rapid to capture using direct, real-time observation methods1-6. Current approaches rely mainly on time-resolved spectra derived from short-pulsed lasers with appropriate wavelengths and pulse widths for the target phenomena7-10, supplemented by some experimental techniques combined with theoretical simulations11-14. In contrast, if a material exhibits sufficiently slow changes after photoexcitation, its structures and physical properties can be directly observed and compared with theoretical and spectroscopic results. This article explores the magnetic and structural properties of a new material that displays slow relaxation from UV-excited states. The study demonstrates that both valence and inner-shell electrons are cooperatively photoexcited, transitioning to a new state influenced by spin, charge, and orbital degrees of freedom. Unlike traditional theoretical descriptions, which assume time-independent atomic orbitals as the basis for molecular orbitals, this research reveals that atomic orbitals are time-dependent during these processes. These findings offer a foundational understanding of the relaxation processes from photoexcited states and provide insights into general chemical reactions. Physical sciences/Physics/Chemical physics Physical sciences/Materials science/Condensed-matter physics/Magnetic properties and materials Figures Figure 1 Figure 2 Figure 3 Figure 4 UV-excitation-responsive materials Scientists have long aspired to observe the detailed processes of dynamic changes triggered by photoexcitation in real time 15-18 . Such processes often occur in mixtures that lack well-defined atomic positions. This lack of structure makes real-time observation of detailed changes in structures and physical properties even more challenging, even when some processes are slow. Previously, exceptional materials based on charge-transfer complexes containing photoreactive species were found to exhibit unusually slow or progressive changes upon UV irradiation in single crystals 19,20 . However, their photoexcitation and relaxation processes remained too rapid to observe real-time structural changes and the evolution of physical properties using standard experimental methods. Additionally, UV irradiation caused serious disorder or amorphization in the crystals, preventing detailed structural analyses. In this work, we synthesized a new charge-transfer salt, MV[Au(dmit) 2 ] 2 (MV salt; Figs. 1a and b and Extended Data Figs. 1a and b), which undergoes sufficiently slow changes in the molecular structure after UV irradiation (~240–450 nm, 5 min) on single crystals, enabling detailed structural analyses during the change. Based on single-crystal X-ray structural analyses, the change mainly involved Au atoms at the centre of the Au(dmit) 2 molecules and lasted for months (~2,500 h, Extended Data Fig. 2) with intermittent structural changes. Before UV irradiation, all Au(dmit) 2 molecules in the MV salt were almost completely planar, as is typical for Au(III) complexes 21 . Approximately 200 h after the cessation of brief (~5–10 min) UV irradiation ( t = 0 h) of the single crystals, 2%–3% of the Au atoms began to deviate from the molecular plane as disordered atoms (Fig. 1c and Extended Data Figs. 1–2). The non-planar coordinates of the Au(III) complexes were unusual, suggesting exceptional situations such as transition states during chemical reactions. The distances between the deviated Au atoms and the molecular plane, d (Å), in non-planar Au2 and Au3 alternately increased and decreased at t ³ 200 h. Specifically, the Au atoms fluctuated between three sites following UV irradiation; thus, the structure also fluctuated among the three structures: planar Au1, non-planar Au2, and non-planar Au3. Structural changes occurred after the cessation of UV irradiation, excluding heating effects or decomposition by UV irradiation as the cause of the structural changes. However, single-crystal X-ray structural analyses indicated that 97%–98% of the Au atoms adopted the original planar coordinates (Extended Data Figs. 1–2). The X-ray oscillation photographs used in the structural analyses changed depending on the elapsed time t , indicating that the sample fluctuated between highly and poorly crystalline states (Fig. 1d and Extended Data Figs. 3–4). Because single-crystal X-ray structural analyses reveal only long-range ordered atomic arrangements, and because UV excitation may seriously disturb the atomic arrangement and electron distribution in the single crystals, we cross-checked the UV-induced structural change using a different measurement method requiring no long-range order in the samples. We examined the real-time X-ray absorption fine structure (XAFS) 22 of the Au L III -edge using single crystals of the MV salt (Extended Data Figs. 5a–f) and the same UV light source used in the single-crystal X-ray structural analyses. The XAFS spectra demonstrated that most Au atoms (>95%) in the sample had similar coordinate structures and that the Au local structure was retained during and until 270 min after the cessation of irradiation. The structure of the MV salt progressively changed, while retaining the appearance of a single crystal. Because such disorder effects are particularly evident in the early stages of relaxation, deviated Au atoms were hardly observed at t £ 200 h using single-crystal X-ray structural analyses. Further analysis of the X-ray oscillation photographs revealed that most crystal planes exhibited long-lasting lattice distortions with fluctuations in the single crystal of the MV salt after UV irradiation (Extended Data Figs. 6a and b). Based on single-crystal X-ray structural analyses, we clarified that UV excitation caused the Au atoms to deviate from the molecular plane and intermittently changed sites, thereby forming planar Au1 and non-planar Au2 and Au3 configurations. The MV salt gradually transitioned from a dark state to a different (meta)stable state. UV-induced intermolecular interactions Upon UV-induced distortion of the molecular structure of Au(dmit) 2 from planar Au1 to non-planar Au2 or Au3, the Au–C distances decreased when the Au atoms deviated (i.e., Au1 > Au2 and Au3), reaching values comparable to the van der Waals distance (Au–C = 3.36 Å) 23 between adjacent molecules (Fig. 2a and Supplementary Table 1), suggesting that UV irradiation induced the intermolecular interactions. Intermolecular interactions are the starting points of chemical reactions 24,25 , phase transitions 26,27 , and various other phenomena 28,29 . While these interactions stabilize the total (Gibbs) energy of the MV salt, the distortion of the Au coordinate destabilizes the delocalization energy of the Au(dmit) 2 molecules. The disorder at the Au site decreases the Gibbs energy by increasing entropy; however, it is unfavourable for intermolecular interactions between pairs of facing molecules, such as MV–Au(dmit) 2 and Au(dmit) 2 –Au(dmit) 2 . To quantify the net effects of these opposing factors on stability, we calculated the intermolecular interactions and thermodynamic properties of the observed structures using density functional theory (DFT) 30 (Extended Data Fig. 7). The calculated molecular orbitals (MOs) show that intermolecular interactions after UV irradiation due to extensive delocalization of electrons over neighbouring molecules. This delocalization is more prominent around the non-planar coordinated Au(dmit) 2 (Au2(dmit) 2 or Au3(dmit) 2 ) molecules compared to that of the planar Au(dmit) 2 (Au1(dmit) 2 ) molecules (Fig. 2b). This UV excitation induces delocalization. Similarly, the Mulliken charges 31 on the Au atoms (Fig. 2c) and the Gibbs energy (Fig. 2d) consistently demonstrate that the Au(dmit) 2 molecules exchange energy and charge between neighbouring molecules. However, the thermodynamic quantities of each structure (Au1(dmit) 2 , Au2(dmit) 2 , and Au3(dmit) 2 ) repeatedly increase and decrease with t (Extended Data Fig. 7). Meanwhile, they retain their average values for each structure until t ~ 2,000 h. The same calculation also shows the importance of the Au2 and Au3 non-planar structures in the charge and spin distributions when the Au(dmit) 2 molecules possess unpaired electrons (Fig. 2e). In summary, UV-irradiation-induced intermolecular interactions cause continuous fluctuations in the energies, charges, and structures of the MV salt, driven by charge, spin, and orbital degrees of freedom. Real-time atomic-level observation X-ray photoelectron spectroscopy (XPS) is well known as a powerful tool for surface analyses 32 and is useful for selective analyses of the net UV-affected region in bulk materials, as UV penetrates solids much deeper (a few micrometres) than the photoelectron escape depth (a few Angstroms) 33 . The first-principles calculations (Figs. 2b and e) indicate that the Au and S atoms dominate the electron and spin densities in the MV salt. Therefore, we focused on the XPS of the Au and S atomic orbitals, which were continuously monitored before (dark), during ( t = 0), and after UV irradiation ( t > 0) (Figs. 3a–f, Extended Data Figs. 8a–d, and Supplementary Figs. 5a–e). Upon UV irradiation, all observed XPS peaks (Figs. 3a–c and e and Extended Data Figs. 8a–d) significantly shift to shallower binding energies (BEs). Such peak shifts are generally understood as changes in the oxidation states of the atoms 34 . In this work, photoexcitation causes optical transitions of electrons, which correspond to transient changes in the oxidation states of the atoms. In other words, the observed XPS spectral changes indicate that the energy of the MV salt is enhanced by the photon energy. The Au 5 s (Fig. 3b) and S 2 p (Extended Data Figs. 8c and d) spectra recover their original (dark) BE values by ~3,000 h, whereas the remaining atomic orbitals change to shallower BE values quite different from those during UV irradiation or under dark conditions. These differences in relaxation behaviour are correlated with the degrees of freedom, viz . , the Au 4 f and 4 d orbitals exhibit more complicated and larger responses than the s and p orbitals of both the Au and S atoms. Furthermore, the Au 4 f 5/2 and Au 4 f 7/2 peaks broaden after UV irradiation (Fig. 3a and Supplementary Fig. 5a) and then gradually become sharper. This finding indicates that UV irradiation produces various photoexcited states close to each other in energy and that they gradually converge into fewer states during the relaxation processes. The peak separation between the Au 4 f 5/2 and Au 4 f 7/2 peaks, viz ., the spin–orbit coupling in the Au 4 f orbitals, increases with time, which indicates that the orbitals change in shape (see Supplementary Notes 1–3 in the Supplementary Information) 35 . We observed the electrons and MOs in transition to a different steady state after the cessation of UV irradiation. Furthermore, the 4 f 5/2 –4 f 7/2 peak intensity ratio becomes increasingly imbalanced over time (Fig. 3d), indicating that spin polarization occurs around the Au 4 f orbitals. A similar trend is observed for the Au 4 d orbitals (Fig. 3f). The MV salt is magnetized spontaneously and transiently. Real-time observation of electrons To observe the occurrence and evolution of spin polarization after UV irradiation, we repeated the measurements of the temperature dependence of the magnetic susceptibility of the MV salt before (dark) and after UV irradiation (Figs. 4a–e). Under the dark conditions, the temperature ( T )-independent small susceptibility (~3 ´ 10 – 4 , Fig. 4a) indicates that the salt is effectively diamagnetic except for a negligible number of antiferromagnetically interacting spins manifested at T £ 10 K. This finding is consistent with the fact that practically no unpaired electrons exist in the MV salt in the ground state, except for a small number of unpaired electrons produced by weak MV–Au(dmit) 2 CT interactions, as observed for a related compound 20 . However, after UV irradiation, paramagnetic behaviour is observed with large hysteresis between the zero-field cooling (ZFC) and field-cooling (FC) processes (Figs. 4b–e). Note that the susceptibility c is negative, in contrast to the standard paramagnetism ( c > 0) 36 . This magnetic susceptibility can be explained if the unpaired electrons occupy significantly high energy levels with large orbital angular momenta. Such a situation is possible in the excited states caused by the Au 4 f –Au n f and Au 4 d –Au n d transitions (4 < n). This result is consistent with the above discussion of XPS, indicating that we observed how the spins polarized. Additionally, alternating increases and decreases in the hysteresis occur between FC and ZFC (Figs. 4b–e). The observed period (~30 h) depends on the time interval of the measurements and should be independent of the intrinsic oscillation periods of the spin system. However, this characteristic still demonstrates that the spin system fluctuates significantly during the relaxation processes after the cessation of UV irradiation. Discussion This work supports the analysis of physical and chemical processes in time-resolved spectroscopy 37,38 . Different (meta)stable states are separated by an energy barrier, preventing spontaneous transitions between states. Consistently, in this work, some of the atomic orbitals spontaneously destabilized themselves (Fig. 2d) with alternating stabilization and destabilization after the cessation of photoexcitation, whereas the total (Gibbs) energy of the system decreased during these processes. Because the chemical species in the system do not simultaneously behave in the same manner, one transiently observes the averaged structure, properties, and energy of different species as a snapshot of fluctuation. The XPS spectra also indicate that the core electrons cooperate to achieve a new stable state by exchanging their energies with each other and with their surroundings using their spin, charge, and orbital degrees of freedom. The observed structural and property changes should include the general aspects of chemical and physical changes. For example, in the material design and discussion of the mechanisms of electro- 39 and photoluminescence 40 and solar cells 41 , a few characteristic MOs around the valence bands/orbitals of key compounds are usually paid the most attention. The gradual and persistent changes in the closed-shell core electrons observed in this work contrast sharply with the rule of thumb that valence electrons dominate chemistry. All atomic orbitals cooperate to rearrange their chemical bonds for relaxation in response to large perturbations, such as photoexcitation and chemical reactions. During slow structural changes after UV excitation, the valence and inner-shell electrons cooperate to polarize their spins and charges by exchanging their energies with each other and with their surroundings using the available degrees of freedom. This behaviour can be macroscopically observed as fluctuations in structure, properties, and energy. Based on the orbital approximation, by gradually and continuously adjusting the energy levels and spin states, the atomic orbitals at deeper levels possessing larger degrees of freedom can play dominant roles in stabilizing both the transient and final states during molecular orbital reconstruction. Some atomic orbitals had energy levels higher than their initial states after spontaneous changes. 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Guidelines to calculate non-radiative deactivation mechanisms of ruthenium tris(bipyridine) derivatives. Coord. Chem. Rev. 510 , 215819 (2024) (DOI 10.1016/j.ccr.2024.215819) Kim, D., Yun, T., An, S. & Lee, C.-L. How to improve the structural stabilities of halide perovskite quantum dots: Review of various strategies to enhance the structural stabilities of halide perovskite quantum dots. Nano Converg. 11 , 4 (2024) (DOI 10.1186/s40580-024-00412-x) Methods Synthesis procedures The starting materials, MV·I 2 42 and TBA[Au(dmit) 2 ] 43 , were prepared following the literature. Acetonitrile (FUJIFILM Wako Pure Chemical Corporation, super-dehydrated for organic synthesis) was procured and used without further purification. Single crystals of MV[Au(dmit) 2 ] 2 were synthesized using a slow metathesis approach called the ‘diffusion method’. MV·I 2 (1,1'-dimethyl-4,4'-bipyridinium diiodide; 1.32 mg, 3.0 mmol) and TBA[Au(dmit) 2 ] (tetrabutylammonium bis(1,3-dithiole-2-thione-4,5-dithiolato)aurate(III); 5.41 mg, 6.5 mmol) were precipitated in CH 3 CN (90 mL) in separate compartments of a three-compartment H-tube with fine porous glass frits (No. 3) in a N 2 atmosphere under dark conditions at 296 K. The two reactants were allowed to dissolve slowly in the solvent, diffuse, and react. After ~2–3 weeks, black diamond-shaped platelets ~0.5-1 mm in size (b-MV[Au(dmit) 2 ] 2 ) were obtained, along with an a polymorph of black hexagonal platelets ~0.5-1 mm in size (a-MV[Au(dmit) 2 ] 2 ). The a-type salt did not exhibit similar physical and structural properties after UV irradiation. Therefore, this paper only refers to the b-type salt without specifying the type. The UV–vis absorption spectra of MV·I 2 , TBA[Au(dmit) 2 ], and MV[Au(dmit) 2 ] 2 are shown in Supplementary Fig. 1. The UV–vis–NIR spectra in the solution and solid state (powder) were recorded using a JASCO V-630 in transmittance mode at 295 K. MV·I 2 and TBA[Au(dmit) 2 ] were dissolved in CH 3 CN (1.92 ´ 10 – 5 M) and CH 3 OH (2.06 ´ 10 – 5 M), respectively, and the baseline (the absorption by the quartz cell and solvent) was independently recorded and subtracted from each spectrum. The measurement conditions were as follows: data response = fast, scan rate = 200 nm min – 1 , and data interval = 2 nm. The single crystals of MV·I 2 and MV[Au(dmit) 2 ] 2 were separately well ground with Al 2 O 3 (white fused alumina, 3000 mesh, Fujimi Incorporated) in an agate mortar, sandwiched between optical quartz plates, and subjected to spectrum measurement. The background (the quartz plates and Al 2 O 3 powder) was independently recorded and subtracted from the sample spectra. TBA[Au(dmit) 2 ] was finely powdered in an agate mortar without Al 2 O 3 , sandwiched between the quartz plates, and subjected to spectrum measurement under identical measurement conditions. The background (the quartz plates) was independently recorded and subtracted from the sample spectra. UV irradiation Single-crystal X-ray structural analyses were performed under different UV irradiation conditions (light source, bandpass filter, mirror module, light intensity, and irradiation duration). The photoresponses did not qualitatively change when the irradiation wavelengths were in the range of ~240–500 nm. This observation is consistent with the solid-state absorption spectra of MV[Au(dmit) 2 ] 2 and related materials (SupplementaryFig. 1), which show main absorption peaks in this region. Two UV light sources were used in this study: a SUPERCURE-203S (200 W, Hg/Xe lamp, SAN-EI ELECTRIC, 220–1,100 nm) for the XAFS and XPS analyses and MAX-350 (300 W, Xe lamp, ASAHI SPECTRA, 250–1,050 nm) for the single-crystal X-ray structural analyses. For X-ray structural analysis, which requires intense light to deeply penetrate single crystals, the more powerful MAX-350 light source was chosen. Both light sources were equipped with input power adjusters, multimode optical quartz fibres (core diameter: 5 mm, length: 1 m), bandpass filters, and mirror modules to select the output wavelengths and adjust the light intensities. The distance between the single-crystal sample and the optical fibre end was ~13 mm for both XAFS and the single-crystal X-ray structural analyses. The light intensity at the sample position was estimated using a Si-diode power metre (NOVA, OPHIR); the specifications of the light sources were provided by the suppliers. The wavelengths used were 250–450 nm for XAFS and 300–600 nm for the single-crystal X-ray structural analyses. The intensities were maintained constant through different measurement runs at ~1 W cm – 2 for both XAFS and single-crystal X-ray structural analyses. The sample temperature during the UV irradiation was not corrected. Other details of the UV irradiation have been described in our previous paper. 20,44 Single-crystal X-ray structural analyses Prior to performing X-ray structural analysis and physical property/spectroscopic measurements (electrical resistivity, magnetic susceptibility, XPS, and XAFS) on the new sample, the crystallinity was examined using X-ray oscillation photographs obtained using a VariMax RAPID/a at the Advanced Research Support Centre (ADRES), Ehime University. High-quality single crystals (accuracy ³90%) were first analysed at 298 K in the dark to confirm their initial structures before UV irradiation. Data were collected at ADRES using a Rigaku VariMax Saturn CCD724/a detector equipped with a Mo rotor anode ( l = 0.71073 Å). For each single crystal, X-ray oscillation photographs (1,440—2,880 frames) were collected, a process that generally requires 2–4 h per crystal. The structural analysis temperature was carefully chosen by considering the relaxation rates from the UV-excited states and the thermal motion of atoms, both of which can depend on temperature. Lower temperatures are advantageous for observing crystal structures due to reduced thermal motion. 45 However, relaxation at extremely low temperatures, such as 77 K, was expected to be too slow to monitor until complete relaxation, based on ESR experiments conducted on a related material. 20 Considering the possible temperature increase under UV irradiation, the initial temperature for data collection was tentatively set to 128 K. For data collection at 128 K, the samples were cooled to 128 K at a rate of -1 K min – 1 under dark conditions to avoid unnecessary disorder, inhomogeneity, or possible supercooling. After 10 hours, corresponding to the initial rapid relaxation period estimated from the behaviour of related materials, the samples were warmed to 298 K at a rate of +1 K min - 1 . 20 For structural analysis during relaxation, a single crystal was first exposed to UV radiation for 5 min. The crystal was then maintained at 128 K for 10 h following the cessation of UV irradiation. After 10 h, the crystal was stored at 298 K, except during the data collection at 128 K. The temperature variation rates were 1 K min - 1 between 128 K and 298 K. All single-crystal X-ray structural analyses were performed at 128 K, and all structures were based on the same single crystal. The structure during UV irradiation could be completely solved with (~0.2%) or without non-planar-coordinated Au atoms (structures Au2 and Au3) with equal reliability. Therefore, the structure under UV irradiation is not discussed in detail. Regardless of whether the crystal was exposed to UV irradiation, 18 frames of oscillation photographs were taken at both the beginning and end of each data collection run to detect any artefacts such as (partial) decomposition, microcracks, and other types of deterioration of the crystal caused by temperature variation or UV irradiation. The collected data were first processed using CrysAlisPro ver.41_64.93a (Rigaku) and then analysed using Olex 2. 46 The details of data collection, data processing, and structural analyses, which mainly consisted of standard procedures, are summarized in crystal information format (cif) files deposited to The Cambridge Crystallographic Data Centre (SupplementaryTable 2). XAFS The X-ray absorption spectra were obtained using beamline 15A1 at the Photon Factory of the High Energy Accelerator Research Organization. X-rays from the 2.5 GeV storage ring were monochromatized using a Si(111) double crystal. The spectra were recorded at ambient temperature and pressure. The samples were single crystals of MV[Au(dmit) 2 ] 2 , freshly prepared, stored in the dark, and examined by single-crystal X-ray structural analyses to confirm they were high-quality single crystals without non-planar coordinated Au atoms. Controlling the thickness of the single crystals was not possible, leading to variations between crystals that significantly affected the signal-to-background ratio in both XAFS detection modes (fluorescence and transmittance). The spectra were expected to depend on the beam positions on the crystal surface because of possible inhomogeneity during and after UV irradiation. Accordingly, micro-XAFS was performed using a beam size of 17 mm (horizontal)×32 mm (vertical) mm 2 . The X-ray beam (~12 keV) was incident upon the most developed faces (the ab planes) of the diamond-shaped crystals at an incident angle of 45°, to detect both the fluorescence and transmitted X-rays simultaneously using a custom-built Lytle detector and an ion chamber, respectively. The spectra of three single crystals in each salt (~0.4×0.3× d mm 3 in dimension: d = 0.008–0.07 mm) were recorded to examine sample dependence and reproducibility. Every time a single crystal was set in the holder, a 2D map of the fluorescence/transmission intensity was collected by raster scanning the sample with a 20 mm step. The Au L III absorption edge energy was calibrated using Au foil. While aligning the polarization angles of the incident X-rays along and perpendicular to the molecular planes of Au(dmit) 2 could detect the deviated Au atoms most sensitively, no such polarization angle existed due to the different stacking directions of Au(dmit) 2 columns in the unit cell. Preliminary spectra obtained with the polarization angles of the // and ^ b -axis in the ab plane exhibited only minor differences; hence, polarization dependence was not examined further. Initially, the ‘dark’ spectra were obtained as described. Next, the same sample was continuously exposed to UV light, during which the spectra were collected. The distance between the sample and the end of the light guide was 10 mm. To confirm the UV-irradiation time and sample dependencies of XAFS, we recorded spectra using different crystals under the same conditions, except for the UV-irradiation time (5 min). The obtained spectra quantitatively agreed with each other. Immediately after the cessation of UV irradiation ( t = 0 min), the spectra were repeatedly collected under the same conditions. Each spectrum was the average of 5–10 recordings, each taking 15–30 min. The spectra did not change after being repeatedly recorded at the same position on the crystal within this time. However, the XAFS spectra change irreversibly after prolonged (³45 min) synchrotron X-ray irradiation at ~12 keV. We collected several XAFS spectra at different positions on the same sample to confirm reproducibility and homogeneity. The samples used in the XAFS analysis were checked afterwards by single-crystal X-ray structural analyses to confirm that they retained their original structure and crystal quality without decomposition or deterioration. XPS XPS spectra were recorded using the single crystals covering a conducting C tape (~1.5 ´ 1.5 mm 2 , Nisshin EM) and a spectrometer JEOL JPS 9200 (Mg K a (1,253.6 eV, 12 kV, 40 mA)). The base pressure in the main chamber was ~6.6 ´ 10 – 7 and ~7.8 ´ 10 – 6 Pa with and without X-ray irradiation, respectively. The charge-up effects on the BE were corrected using the C 1 s peak of the C tape (graphite). An electrostatic objective lens was used, whereas a magnetic objective lens was not. The field of view was 3.0 mm. We examined the Au 4 d 3/2 , Au 4 d 5/2 , Au 4 f 5/2 , Au 4 f 7/2 , Au 5 s , S 2 s , S 2 p 1/2 , and S 2 p 3/2 spectral regions at ~298 K. First, the stabilities of the samples under continuous X-ray irradiation were examined. The spectra remain unchanged after several months of continuous X-ray irradiation. The best measurement conditions were determined to be in the dark (Extended Data Table 1). The S 2 p 1/2 and S 2 p 3/2 peaks could not be resolved as separate peaks because the energy difference between them is smaller than the spectrometer's resolution (~0.9 eV), resulting in the observation of a single merged peak. The sample was then removed from the spectrometer and exposed to UV irradiation in air for 5 min using the Hg/Xe lamp described above (200 W, the range of 250—450 nm was selected using a bandpass filter and an Al mirror). The distance between the end of the optical fibre and the sample was ~1 cm. For comparison, we performed XPS on an independently prepared sample of the same material under dark conditions, and we then exposed the sample (in the main chamber) to UV light from the same light source through the quartz window of the main chamber, during which we conducted XPS under UV irradiation (~1 h). The distance between the sample and the end of the optical fibre was ~30 cm. The XPS spectra after cessation of UV irradiation were consistent between the two UV irradiation conditions, demonstrating that the results were qualitatively independent of the UV irradiation conditions. Because Ar sputtering irreversibly changes the spectra with poor reproducibility, the sample surface was not etched prior to collecting the XPS spectra presented in this paper. Recording the series of spectra required ~1 h. The obtained spectra were distinguished by the elapsed time t (h) after the cessation of UV irradiation, which was defined as the time at which we began collecting every series of XPS spectra. The spectrum at t = 0 (h) was obtained during UV irradiation. The XPS spectra were continuously recorded until t = 300 h, after which spectra were collected every 24 h until t = 3,000 h. The obtained spectra were analysed by curve fitting using SpecSurf ver. 1.9.2.12 (2012, JEOL Ltd.) to obtain the BEs and intensities. The intensity is the peak area derived from the photoelectron counts (cps) multiplied times the acquisition time (s) and integrated along the BE (eV) across the peak widths. Physical property measurements Electrical resistivity was measured at 296 K using crystals, a custom-built cryostat, and the standard two-probe method with a constant direct current. Magnetic susceptibility was assessed using polycrystalline samples with a magnetic property measurement system MPMS-XL7 (Quantum Design). Detailed methods for these measurements can be found in our previous publication. 20,43,47,48 Theoretical calculations DFT calculations (R w B97XD/LanL2DZ(5d, 7f)) were performed using Gaussian 16 31 and GaussView 6.1.1. 49 To obtain the energies of the three structural types of Au(dmit) 2 anions in the solid state, X-ray molecular structures were utilized without structural optimization. The electronic energy and thermodynamic quantities were calculated for a simplified system containing only the Au(dmit) 2 anion and MV cation. To examine model dependence, we performed similar calculations using systems with one molecule (MV or Au(dmit) 2 ) and two molecules (MV–Au(dmit) 2 or Au(dmit) 2 –Au(dmit) 2 ). The results indicated that the molecular systems depicted in Supplementary Figs. 4a–c were more appropriate than the remaining models. Data availability Source data (crystallographic information format (cif) files) for Figs. 1b–d, 2a, and 2c as well as Extended Data Figs. 1–4, and 6 were deposited at the Cambridge Crystallographic Data Centre, with the registry numbers summarized in Supplementary Table 2. The data were obtained free of charge from The Cambridge Crystallographic Data Centre at www.ccdc.cam.ac.uk/data_request/cif. The source data for Figs. 2b–e, 3a–f, and 4a–e as well as Extended Data Figs. 5a–f, 7a–d, and 8a–d are provided with this paper in the Supplementary Information. 42. Naito, T., et al. Simultaneous control of carriers and localized spins with light in organic materials. Adv. Mater. 24 , 6153–6157 (2012) (DOI 10.1002/adma.201203153 ) 43. Steimecke, G., Sieler, H.-J., Kirmse, R. & Hoyer, E. 1.3-Dithiol-2-thion-4.5-dithiolat aus Schwefelkohlenstoff und alkalimetall. Phosphorus Sulfur Relat. Elem. 7 , 49–55 (1979) (DOI 10.1080/03086647808069922 ) 44. Naito, T., et al. UV-vis-Induced vitrification of a molecular crystal. Adv. Funct. Mater. 17 , 1663–1670 (2007) (DOI 10.1002/adfm.200600583 ) 45. Wright, J. D. Molecular motion in crystals’ in Molecular Crystals . 2 nd ed, Chap. 5 74–96 (Wiltshire: Cambridge University Press, 2024), GB 46. Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 42 , 339–341 (2009) (DOI 10.1107/S0021889808042726 ) 47. Naito, T., et al. Molecular photoconductor with simultaneously photocontrollable localized spins . J. Am. Chem. Soc. 134 , 18656–18666 (2012) (DOI 10.1021/ja306260b ) 48. Naito, T., Inabe, T., Niimi, H. & Asakura, K. Light-induced transformation of molecular materials into devices. Adv. Mater. 16 , 1786 – 1790 ( 2004 ) (DOI 10.1002/adma.200400308 ) 49. Dennington, R., Keith, T. A. & Millam, J. M. GaussView. version 6.1.1 (Shawnee Mission KS: Semichem Inc., 2016) Declarations Acknowledgements The authors are grateful to T. Tsuneda at Hokkaido University for valuable discussions regarding the DFT calculations. The authors would like to thank S. Mori and R. Konishi at ADRES, Ehime University, for their single-crystal X-ray structural analyses, experimental advice, assistance with troubleshooting of the hardware and software, and productive discussions. The authors are grateful to K. Konishi for assistance and valuable advice in using the SQUID. They are also grateful to K. Asakura at the Institute for Catalysis, Hokkaido University, for the valuable assistance with the XAFS experiments. The XAFS experiments were performed with the approval of the Photon Factory Program Advisory Committee (Proposal No. 2022G104). This work was partially funded by a Grant-in-Aid for Challenging Exploratory Research (18K19061) from the JSPS, the Iketani Science and Technology Foundation (ISTF; 0331005-A), the Research Grant Program of the Futaba Foundation, the Casio Science Promotion Foundation, an Ehime University Grant for Project for the Promotion of Industry/University Cooperation, and the Canon Foundation (Science and Technology that Achieve a Good Future). Author contributions T.N. conceived and supervised the project, designed almost all experiments, confirmed the experimental results, checked the analyses, and wrote the paper. Under the instruction of T.N., Y.M. synthesized the compound, including its single crystals; S.S. performed preliminary studies on the single-crystal X-ray structural analyses and theoretical calculations; M.N. and Y.N. performed the single-crystal X-ray structural analysis and the first-principles calculations; K.M. recorded the XPS spectra; and K.M. and M.N. measured the magnetic susceptibility. Y.T., Y.N., and T.N. collaborated to obtain the XAFS spectra. All the authors discussed the results and commented on the manuscript. Competing interests The authors declare no competing interests. Additional information Supplementary Information The online version contains supplementary material available at https://doi.org/...... Materials & Correspondence Correspondence and requests for materials should be addressed to Toshio Naito ( [email protected] ). Reprints and permissions information is available at http://www.nature.com/reprints. Additional Declarations There is NO Competing Interest. Supplementary Files ExtendedData.docx SI4.docx Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4811531","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":343798197,"identity":"9796f6ca-e124-471f-9baf-a8c96722432c","order_by":0,"name":"Toshio Naito","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYJCCAwwMNgwGzAiBBLzKeUBaDjCkkagFaM1hBgOiHWUv3fzw8IeK83Lm7NyJDxjbGOT5GxiePcBri8wxgwMHztw2tmzm3WwA1GI44wBDOl4reSQSDA4cbLuduOEw7zbpv20MjBsYGNIk8GtJ/wDUcq4eqGX7D6At9kRoyQHZciDBAGgLA1BLImEtN3IKDpw5k2wItGWzBMM5ieQZhwn4hX1G+uYPFRV28gbnz278wFBmY9vf3pP2AJ8WdAB0EjNPGik6IDYfI1nLKBgFo2AUDGsAANz7SV+M6apEAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-0908-2730","institution":"Ehime University","correspondingAuthor":true,"prefix":"","firstName":"Toshio","middleName":"","lastName":"Naito","suffix":""},{"id":343798198,"identity":"b8e4782b-2647-4896-a5c3-8de6d620be21","order_by":1,"name":"Minaho Nakaie","email":"","orcid":"","institution":"Ehime University","correspondingAuthor":false,"prefix":"","firstName":"Minaho","middleName":"","lastName":"Nakaie","suffix":""},{"id":343798199,"identity":"ba400b54-f757-4f30-b67f-c477a57f307e","order_by":2,"name":"Kaito Murakami","email":"","orcid":"","institution":"Ehime University","correspondingAuthor":false,"prefix":"","firstName":"Kaito","middleName":"","lastName":"Murakami","suffix":""},{"id":343798200,"identity":"0360d374-0467-487e-9816-57d01e034c43","order_by":3,"name":"Yuka Nishiyama","email":"","orcid":"","institution":"Ehime University","correspondingAuthor":false,"prefix":"","firstName":"Yuka","middleName":"","lastName":"Nishiyama","suffix":""},{"id":343798201,"identity":"f9349eac-5fb2-4c04-8532-cb86b01255c4","order_by":4,"name":"Shuji Shiose","email":"","orcid":"","institution":"Ehime University","correspondingAuthor":false,"prefix":"","firstName":"Shuji","middleName":"","lastName":"Shiose","suffix":""},{"id":343798202,"identity":"af4ef10c-f1fc-4bc9-9b3a-a441ec275bce","order_by":5,"name":"Yuko Miyaji","email":"","orcid":"","institution":"Ehime University","correspondingAuthor":false,"prefix":"","firstName":"Yuko","middleName":"","lastName":"Miyaji","suffix":""},{"id":343798203,"identity":"640bfc51-d6d2-4352-bf1c-99c883eca8c5","order_by":6,"name":"Yasuo Takeichi","email":"","orcid":"https://orcid.org/0000-0003-3334-0274","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Yasuo","middleName":"","lastName":"Takeichi","suffix":""},{"id":343798204,"identity":"7d55af37-47b7-4c0f-81b2-5024c848aa1d","order_by":7,"name":"Yasuhiro Niwa","email":"","orcid":"https://orcid.org/0000-0001-5808-5594","institution":"Institute of Materials Structure Science","correspondingAuthor":false,"prefix":"","firstName":"Yasuhiro","middleName":"","lastName":"Niwa","suffix":""}],"badges":[],"createdAt":"2024-07-27 06:55:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4811531/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4811531/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":65612431,"identity":"3d914d8d-a623-476d-837e-04e00d4fbfa3","added_by":"auto","created_at":"2024-09-30 13:39:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":791503,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTime evolution of structures and related information about MV[Au(dmit)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e during photoexcitation and succeeding dynamics.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Structural formulas of the [Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e-\u003c/sup\u003e anion and MV\u003csup\u003e2+\u003c/sup\u003e cation. Orange and green frames indicate good and inferior crystal quality, respectively, as distinguished by clear spots regularly arranged in the frame.\u003cstrong\u003e b\u003c/strong\u003e, Molecular structures and arrangement in MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e (194 h since the cessation of UV irradiation). Blue, yellow, brown, orange/white, and pink spheres indicate N, S, C, Au, and H atoms, respectively. \u003cstrong\u003ec\u003c/strong\u003e, Distance between the deviated Au atom and the mean molecular plane of Au(dmit)\u003csub\u003e2\u003c/sub\u003e anions in Au2 or Au3, d (Å: the right vertical axis), and site occupancies (%: the left vertical axis). Experimental errors are ~0.03–0.04 Å and ~0.1% for each datum, i.e. within the plotted markers. \u003cstrong\u003ed\u003c/strong\u003e, X-ray oscillation photographs and molecular structures derived from the analyses of the photographs.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/c50c6df040a07ff09f2e1d03.png"},{"id":65612422,"identity":"e8b4e07f-94a4-43f9-9964-4eb9abafa918","added_by":"auto","created_at":"2024-09-30 13:39:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":823932,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharge and spin distributions and energies as functions of the elapsed time \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003et\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e after the cessation of UV irradiation.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Depending on \u003cem\u003et\u003c/em\u003e, covalent bonds transiently formed between Au and nearest-neighbour C atoms during photoexcitation and succeeding dynamics (Supplementary Fig. 3). Blue, yellow, brown, orange/white, and pink spheres indicate N, S, C, Au, and H atoms, respectively, with Au atoms in three different sites, forming planar Au1 and non-planar Au2 and Au3 structures. \u003cstrong\u003eb\u003c/strong\u003e, MOs calculated for the selected three-molecule system (charge = 0, spin = 0: Supplementary Fig. 4) in MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e based on the observed structures at \u003cem\u003et\u003c/em\u003e = 194 h. \u003cstrong\u003ec\u003c/strong\u003e, Mulliken charges on the Au atoms derived from the DFT calculations based on the observed structures of MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e (128 K). \u003cstrong\u003ed\u003c/strong\u003e, Molar Gibbs free energy \u003cem\u003eG\u003c/em\u003e (298.15 K, 1 atm) of MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e during relaxation after UV irradiation for 5 min. The irradiation stopped at \u003cem\u003et\u003c/em\u003e = 0 h. The energies under the dark conditions are shown at \u003cem\u003et\u003c/em\u003e = 1. Black circles, red squares, and blue triangles indicate the energies of the systems with planar Au(dmit)\u003csub\u003e2\u003c/sub\u003e (Au1) and two different non-planar configurations of Au(dmit)\u003csub\u003e2\u003c/sub\u003e (Au2 and Au3), respectively. Supplementary Figs. 4a–c show their corresponding configurations.\u003cstrong\u003e e\u003c/strong\u003e, MOs (unrestricted for a- and b-spins) and spin distributions in the neutral radical [Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e0\u003c/sup\u003e species (\u003cem\u003es\u003c/em\u003e = 1/2) based on the observed structures at \u003cem\u003et\u003c/em\u003e = 194 h. This structure was selected for the calculations as it contains clearly different Mulliken charges and coordination geometries between Au1, Au2, and Au3, unambiguously representing their differences and characteristics.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/16a48835ff1b7a96b69f712e.png"},{"id":65612426,"identity":"78b62da9-ba34-4c4d-b59c-f1f3c60a04e1","added_by":"auto","created_at":"2024-09-30 13:39:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":898072,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotoexcitation and subsequent dynamics observed by XPS (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003et\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 0–3,000 h).\u003c/strong\u003e \u003cem\u003et\u003c/em\u003e = 0 indicates the XPS data obtained during continuous UV irradiation. \u003cstrong\u003ea\u003c/strong\u003e, Selected spectra showing the time evolution for the initial 300 h. \u003cstrong\u003eb\u003c/strong\u003e, BEs and intensities (\u003cem\u003eI\u003c/em\u003e) of Au 5\u003cem\u003es\u003c/em\u003e spectra normalized by the respective dark data (BE: 89.9119 eV, \u003cem\u003eI\u003c/em\u003e: 280.904). \u003cstrong\u003ec\u003c/strong\u003e, BEs of Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e spectra normalized by the respective dark data (Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e: 75.0158 eV, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e: 71.3327 eV). \u003cstrong\u003ed\u003c/strong\u003e, \u003cem\u003eI\u003c/em\u003e of Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e spectra normalized by the respective dark data (Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e: 1,305.02, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e: 1,730.45). \u003cstrong\u003ee\u003c/strong\u003e, BEs of Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e and 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e spectra normalized by the respective dark data (Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e: 343.654 eV, Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e: 325.292 eV). \u003cstrong\u003ef\u003c/strong\u003e, \u003cem\u003eI\u003c/em\u003e of Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e and 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e spectra normalized by the respective dark data (Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e: 847.99, Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e: 976.99). The insets (Figs. 3b–f) are based on the same data of the corresponding main panels with different scales of the horizontal axes to show clearly the earlier (log scale) and later (linear scale) processes. The values at \u003cem\u003et\u003c/em\u003e = 0 are indicated by green (Au 5\u003cem\u003es\u003c/em\u003e BE in \u003cstrong\u003eb\u003c/strong\u003e, Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e BE in \u003cstrong\u003ee\u003c/strong\u003e, and Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e in \u003cstrong\u003ef\u003c/strong\u003e), blue (Au 5\u003cem\u003es\u003c/em\u003e \u003cem\u003eI\u003c/em\u003e in \u003cstrong\u003eb\u003c/strong\u003e, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e BE in \u003cstrong\u003ec\u003c/strong\u003e, and Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e in \u003cstrong\u003ed\u003c/strong\u003e), red (Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e BE in \u003cstrong\u003ec\u003c/strong\u003e, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e in \u003cstrong\u003ed\u003c/strong\u003e), and orange (Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e BE in \u003cstrong\u003ee\u003c/strong\u003e, and Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e \u003cem\u003eI\u003c/em\u003e in \u003cstrong\u003ef\u003c/strong\u003e) circles in the main panels.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/bff936d41de222a20c594fa7.png"},{"id":65612137,"identity":"7ad9e128-92a9-486d-a876-682fd58b8754","added_by":"auto","created_at":"2024-09-30 13:39:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":324651,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTemperature dependencies of magnetic susceptibility of MV[Au(dmit)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Measured under dark conditions. \u003cstrong\u003eb\u003c/strong\u003e, \u003cem\u003et\u003c/em\u003e = 1 h, \u003cstrong\u003ec\u003c/strong\u003e,\u003cem\u003e t\u003c/em\u003e = 30 h, \u003cstrong\u003ed\u003c/strong\u003e, \u003cem\u003et\u003c/em\u003e = 60 h, \u003cstrong\u003ee\u003c/strong\u003e, \u003cem\u003et\u003c/em\u003e = 90 h. \u003cem\u003et\u003c/em\u003e indicates the elapsed time since the cessation of UV irradiation for 5 min. Each measurement including both FC and ZFC processes required ~14 h, and the indicated time is the beginning of the measurement.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/df5aed0472a7e64a04a44256.png"},{"id":65613150,"identity":"a5ad89e6-bebc-48a0-9f6e-ca0c96068fab","added_by":"auto","created_at":"2024-09-30 13:47:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3343097,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/c249cc91-2e09-4db1-8aa2-e619f931b0fc.pdf"},{"id":65612433,"identity":"aac0c8a8-c2d5-4a12-b64e-1dc8edd75f09","added_by":"auto","created_at":"2024-09-30 13:39:30","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":14478129,"visible":true,"origin":"","legend":"","description":"","filename":"ExtendedData.docx","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/1f083f83542f976cd03f013c.docx"},{"id":65612421,"identity":"c777880d-95dc-4792-bdc6-289cad0bd201","added_by":"auto","created_at":"2024-09-30 13:39:23","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1516267,"visible":true,"origin":"","legend":"","description":"","filename":"SI4.docx","url":"https://assets-eu.researchsquare.com/files/rs-4811531/v1/d7ab66dc5606fc87578f3c06.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Direct observations of slow photo-induced structural and physical changes","fulltext":[{"header":"UV-excitation-responsive materials","content":"\u003cp\u003eScientists have long aspired\u0026nbsp;to observe\u0026nbsp;the\u0026nbsp;detailed processes of\u0026nbsp;dynamic\u0026nbsp;changes triggered by photoexcitation in real time\u003csup\u003e15-18\u003c/sup\u003e. Such processes often\u0026nbsp;occur in mixtures that lack\u0026nbsp;well-defined atomic positions.\u0026nbsp;This lack of structure makes real-time observation of detailed changes in structures and physical properties even more challenging, even when some processes are slow.\u0026nbsp;Previously, exceptional materials based on charge-transfer complexes containing photoreactive species were found to exhibit unusually slow or progressive changes upon UV irradiation in single crystals\u003csup\u003e19,20\u003c/sup\u003e. However, their photoexcitation and relaxation processes\u0026nbsp;remained\u0026nbsp;too rapid to observe real-time\u0026nbsp;structural\u0026nbsp;changes and\u0026nbsp;the\u0026nbsp;evolution of physical properties using standard experimental methods. Additionally, UV irradiation caused serious disorder or amorphization in the crystals, preventing detailed structural analyses. In this work, we\u0026nbsp;synthesized\u0026nbsp;a new charge-transfer salt, MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e (MV salt; Figs. 1a and b and Extended Data Figs. 1a and b), which undergoes sufficiently slow changes in the molecular structure after UV irradiation (~240\u0026ndash;450 nm, 5 min) on single crystals, enabling detailed structural analyses during the change. Based on single-crystal X-ray structural analyses, the change mainly involved Au atoms at the centre of the Au(dmit)\u003csub\u003e2\u003c/sub\u003e molecules and lasted for months (~2,500 h, Extended Data Fig. 2) with intermittent structural changes. Before UV irradiation, all Au(dmit)\u003csub\u003e2\u003c/sub\u003e molecules in the MV salt were almost completely planar, as is typical for Au(III) complexes\u003csup\u003e21\u003c/sup\u003e. Approximately 200 h\u0026nbsp;after\u0026nbsp;the cessation of brief (~5\u0026ndash;10 min) UV\u0026nbsp;irradiation (\u003cem\u003et\u003c/em\u003e = 0 h) of the single crystals, 2%\u0026ndash;3% of the Au atoms began to deviate from the molecular plane as disordered atoms (Fig. 1c and Extended Data Figs. 1\u0026ndash;2). The non-planar coordinates of the Au(III) complexes were unusual, suggesting exceptional situations such as transition states during chemical reactions. The distances between the deviated Au atoms and the molecular plane, \u003cem\u003ed\u003c/em\u003e (\u0026Aring;), in non-planar Au2 and Au3\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ealternately increased and decreased at \u003cem\u003et\u003c/em\u003e \u0026sup3; 200 h. Specifically, the Au atoms fluctuated between three sites following UV irradiation; thus, the structure also fluctuated among the three structures: planar Au1, non-planar Au2, and non-planar Au3. Structural changes occurred after the cessation of UV irradiation, excluding heating effects or decomposition by UV irradiation as the cause of the structural changes. However, single-crystal X-ray structural analyses indicated that 97%\u0026ndash;98% of the Au atoms adopted the original planar coordinates (Extended Data Figs. 1\u0026ndash;2). The X-ray oscillation photographs used in the structural analyses changed depending on the elapsed time \u003cem\u003et\u003c/em\u003e, indicating that the sample fluctuated between highly and poorly crystalline states (Fig. 1d and Extended Data\u0026nbsp;Figs. 3\u0026ndash;4).\u0026nbsp;Because\u0026nbsp;single-crystal X-ray structural analyses reveal only long-range\u0026nbsp;ordered atomic arrangements, and\u0026nbsp;because\u0026nbsp;UV\u0026nbsp;excitation may seriously disturb the atomic arrangement and electron distribution in the single crystals, we cross-checked the UV-induced structural change using a different measurement method requiring no long-range order in\u0026nbsp;the\u0026nbsp;samples.\u0026nbsp;We\u0026nbsp;examined\u0026nbsp;the\u0026nbsp;real-time X-ray absorption fine structure (XAFS)\u003csup\u003e22\u003c/sup\u003e of the Au \u003cem\u003eL\u003c/em\u003e\u003csub\u003eIII\u003c/sub\u003e-edge using single crystals of the MV salt (Extended Data\u0026nbsp;Figs. 5a\u0026ndash;f) and the same UV light source used in the single-crystal X-ray structural analyses. The XAFS spectra demonstrated that\u0026nbsp;most\u0026nbsp;Au atoms (\u0026gt;95%) in the sample\u0026nbsp;had\u0026nbsp;similar coordinate structures\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eand that the Au local structure was retained during and until 270 min after the cessation of irradiation.\u003c/p\u003e\n\u003cp\u003eThe structure of the MV salt progressively changed, while retaining the appearance of a single crystal. Because such disorder effects are particularly evident in the early stages of relaxation, deviated Au atoms were hardly observed at \u003cem\u003et\u003c/em\u003e \u0026pound; 200 h using single-crystal X-ray structural analyses. Further analysis of the X-ray oscillation photographs revealed that most crystal planes exhibited long-lasting lattice distortions with fluctuations in the single crystal of the MV salt after UV irradiation (Extended Data Figs. 6a and b). Based on single-crystal X-ray structural analyses, we clarified that UV excitation caused the Au atoms to deviate from the molecular plane and intermittently changed sites, thereby forming planar Au1 and non-planar Au2 and Au3 configurations. The MV salt gradually transitioned from a dark state to a different (meta)stable state.\u003c/p\u003e"},{"header":"UV-induced intermolecular interactions","content":"\u003cp\u003eUpon UV-induced distortion of the molecular structure of Au(dmit)\u003csub\u003e2\u003c/sub\u003e from planar Au1 to non-planar Au2 or Au3, the Au\u0026ndash;C distances decreased when the Au atoms deviated (i.e., Au1 \u0026gt; Au2 and Au3), reaching values comparable to the van der Waals distance (Au\u0026ndash;C = 3.36 \u0026Aring;)\u003csup\u003e23\u003c/sup\u003e between adjacent molecules (Fig. 2a and Supplementary Table 1), suggesting that UV irradiation induced the intermolecular interactions. Intermolecular interactions are the starting points of chemical reactions\u003csup\u003e24,25\u003c/sup\u003e, phase transitions\u003csup\u003e26,27\u003c/sup\u003e, and various\u0026nbsp;other\u0026nbsp;phenomena\u003csup\u003e28,29\u003c/sup\u003e.\u0026nbsp;While these\u0026nbsp;interactions\u0026nbsp;stabilize\u0026nbsp;the total (Gibbs) energy of the MV salt, the distortion of the Au coordinate\u0026nbsp;destabilizes\u0026nbsp;the\u0026nbsp;delocalization\u0026nbsp;energy of the Au(dmit)\u003csub\u003e2\u003c/sub\u003e molecules. The disorder at the Au site decreases the Gibbs energy by increasing entropy; however, it is unfavourable for intermolecular interactions between pairs of facing molecules, such as MV\u0026ndash;Au(dmit)\u003csub\u003e2\u003c/sub\u003e and Au(dmit)\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Au(dmit)\u003csub\u003e2\u003c/sub\u003e. To\u0026nbsp;quantify\u0026nbsp;the net effects\u0026nbsp;of these opposing factors\u0026nbsp;on stability, we calculated\u0026nbsp;the\u0026nbsp;intermolecular interactions and thermodynamic\u0026nbsp;properties\u0026nbsp;of\u0026nbsp;the\u0026nbsp;observed structures using density functional theory (DFT)\u003csup\u003e30\u003c/sup\u003e (Extended Data Fig. 7). The calculated molecular orbitals (MOs) show that intermolecular interactions after UV irradiation due to extensive delocalization of electrons over neighbouring molecules. This delocalization is more prominent around the non-planar coordinated Au(dmit)\u003csub\u003e2\u003c/sub\u003e (Au2(dmit)\u003csub\u003e2\u003c/sub\u003e or Au3(dmit)\u003csub\u003e2\u003c/sub\u003e) molecules\u0026nbsp;compared to\u0026nbsp;that of the planar Au(dmit)\u003csub\u003e2\u003c/sub\u003e (Au1(dmit)\u003csub\u003e2\u003c/sub\u003e) molecules (Fig. 2b).\u0026nbsp;This\u0026nbsp;UV\u0026nbsp;excitation\u0026nbsp;induces delocalization.\u0026nbsp;Similarly,\u0026nbsp;the\u0026nbsp;Mulliken charges\u003csup\u003e31\u003c/sup\u003e on the Au atoms (Fig. 2c) and the Gibbs energy (Fig. 2d) consistently demonstrate that the Au(dmit)\u003csub\u003e2\u003c/sub\u003e molecules exchange energy and charge between neighbouring molecules. However, the thermodynamic quantities of each structure (Au1(dmit)\u003csub\u003e2\u003c/sub\u003e, Au2(dmit)\u003csub\u003e2\u003c/sub\u003e, and Au3(dmit)\u003csub\u003e2\u003c/sub\u003e) repeatedly increase and decrease with \u003cem\u003et\u003c/em\u003e (Extended Data Fig. 7). Meanwhile, they retain their average values for each structure until \u003cem\u003et\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e~\u0026nbsp;2,000 h. The same calculation also shows the importance\u0026nbsp;of the Au2 and Au3 non-planar structures\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ein\u0026nbsp;the\u0026nbsp;charge and spin distributions when the Au(dmit)\u003csub\u003e2\u003c/sub\u003e molecules possess unpaired electrons (Fig. 2e). In summary, UV-irradiation-induced intermolecular interactions cause continuous fluctuations in the energies, charges, and structures of the MV salt, driven by charge, spin, and orbital degrees of freedom.\u003c/p\u003e"},{"header":"Real-time atomic-level observation","content":"\u003cp\u003eX-ray photoelectron spectroscopy (XPS) is well known as a powerful tool for surface\u0026nbsp;analyses\u003csup\u003e32\u003c/sup\u003e and\u0026nbsp;is useful for selective analyses of the net UV-affected region in bulk materials, as UV penetrates solids much deeper\u0026nbsp;(a few\u0026nbsp;micrometres) than the photoelectron escape\u0026nbsp;depth (a few\u0026nbsp;Angstroms)\u003csup\u003e33\u003c/sup\u003e. The first-principles\u0026nbsp;calculations (Figs.\u0026nbsp;2b\u0026nbsp;and\u0026nbsp;e)\u0026nbsp;indicate\u0026nbsp;that the Au and S atoms dominate the electron and spin densities in the MV salt. Therefore, we\u0026nbsp;focused on\u0026nbsp;the XPS of\u0026nbsp;the\u0026nbsp;Au and S atomic orbitals, which were continuously monitored before\u0026nbsp;(dark), during (\u003cem\u003et\u003c/em\u003e = 0), and after UV\u0026nbsp;irradiation (\u003cem\u003et\u003c/em\u003e \u0026gt; 0) (Figs. 3a\u0026ndash;f, Extended Data\u0026nbsp;Figs. 8a\u0026ndash;d, and Supplementary\u0026nbsp;Figs. 5a\u0026ndash;e). Upon UV\u0026nbsp;irradiation, all observed XPS peaks (Figs. 3a\u0026ndash;c\u0026nbsp;and\u0026nbsp;e\u0026nbsp;and\u0026nbsp;Extended Data\u0026nbsp;Figs. 8a\u0026ndash;d) significantly\u0026nbsp;shift\u0026nbsp;to shallower binding\u0026nbsp;energies (BEs). Such peak shifts are generally understood as changes in\u0026nbsp;the\u0026nbsp;oxidation states of the atoms\u003csup\u003e34\u003c/sup\u003e. In this work, photoexcitation causes optical transitions of electrons, which\u0026nbsp;correspond\u0026nbsp;to transient changes in the oxidation states of the atoms. In other words, the observed XPS spectral changes indicate that the energy of the MV salt\u0026nbsp;is\u0026nbsp;enhanced by the photon energy. The Au 5\u003cem\u003es\u003c/em\u003e (Fig. 3b) and S 2\u003cem\u003ep\u003c/em\u003e (Extended Data\u0026nbsp;Figs. 8c\u0026nbsp;and\u0026nbsp;d) spectra\u0026nbsp;recover their\u0026nbsp;original\u0026nbsp;(dark) BE values by ~3,000 h,\u0026nbsp;whereas\u0026nbsp;the remaining atomic orbitals\u0026nbsp;change\u0026nbsp;to shallower BE values quite different from those during UV\u0026nbsp;irradiation or under dark\u0026nbsp;conditions. These differences in relaxation\u0026nbsp;behaviour are correlated\u0026nbsp;with the degrees of freedom, \u003cem\u003eviz\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e,\u0026nbsp;the Au 4\u003cem\u003ef\u003c/em\u003e and 4\u003cem\u003ed\u003c/em\u003e orbitals\u0026nbsp;exhibit\u0026nbsp;more complicated and larger responses than the \u003cem\u003es\u003c/em\u003e and \u003cem\u003ep\u003c/em\u003e orbitals of both\u0026nbsp;the\u0026nbsp;Au and S atoms. Furthermore, the Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e peaks broaden\u0026nbsp;after UV\u0026nbsp;irradiation (Fig. 3a and Supplementary Fig. 5a) and\u0026nbsp;then gradually\u0026nbsp;become\u0026nbsp;sharper. This\u0026nbsp;finding\u0026nbsp;indicates that UV\u0026nbsp;irradiation\u0026nbsp;produces\u0026nbsp;various photoexcited states close to each other in energy and that they gradually\u0026nbsp;converge\u0026nbsp;into fewer states during the relaxation processes. The peak separation between\u0026nbsp;the\u0026nbsp;Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e peaks, \u003cem\u003eviz\u003c/em\u003e.,\u0026nbsp;the spin\u0026ndash;orbit coupling in the Au 4\u003cem\u003ef\u003c/em\u003e orbitals,\u0026nbsp;increases\u0026nbsp;with time, which indicates\u0026nbsp;that\u0026nbsp;the orbitals\u0026nbsp;change\u0026nbsp;in shape (see\u0026nbsp;Supplementary\u0026nbsp;Notes\u0026nbsp;1\u0026ndash;3 in\u0026nbsp;the Supplementary\u0026nbsp;Information)\u003csup\u003e35\u003c/sup\u003e. We\u0026nbsp;observed\u0026nbsp;the electrons and MOs in transition to a different steady state\u0026nbsp;after\u0026nbsp;the cessation of UV\u0026nbsp;irradiation. Furthermore, the 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e\u0026ndash;4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e peak intensity ratio\u0026nbsp;becomes increasingly imbalanced over\u0026nbsp;time (Fig. 3d),\u0026nbsp;indicating\u0026nbsp;that spin\u0026nbsp;polarization occurs\u0026nbsp;around the Au 4\u003cem\u003ef\u003c/em\u003e orbitals.\u0026nbsp;A similar\u0026nbsp;trend is observed\u0026nbsp;for\u0026nbsp;the\u0026nbsp;Au 4\u003cem\u003ed\u003c/em\u003e orbitals (Fig. 3f).\u0026nbsp;The\u0026nbsp;MV salt\u0026nbsp;is magnetized\u0026nbsp;spontaneously and transiently.\u003c/p\u003e"},{"header":"Real-time observation of electrons","content":"\u003cp\u003eTo observe the\u0026nbsp;occurrence and evolution of\u0026nbsp;spin\u0026nbsp;polarization after\u0026nbsp;UV irradiation, we repeated\u0026nbsp;the\u0026nbsp;measurements of the temperature dependence of\u0026nbsp;the\u0026nbsp;magnetic susceptibility of the MV salt before\u0026nbsp;(dark) and after UV irradiation (Figs. 4a\u0026ndash;e). Under the dark conditions, the temperature (\u003cem\u003eT\u003c/em\u003e)-independent small susceptibility (~3\u0026nbsp;\u0026acute;\u0026nbsp;10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e4\u003c/sup\u003e, Fig. 4a) indicates that the salt is effectively diamagnetic except for a negligible number of antiferromagnetically interacting spins manifested at \u003cem\u003eT\u003c/em\u003e \u0026pound;\u0026nbsp;10 K. This\u0026nbsp;finding\u0026nbsp;is consistent with the\u0026nbsp;fact\u0026nbsp;that practically no unpaired electrons\u0026nbsp;exist\u0026nbsp;in the MV salt\u0026nbsp;in\u0026nbsp;the ground state, except for\u0026nbsp;a\u0026nbsp;small number of unpaired electrons produced by weak MV\u0026ndash;Au(dmit)\u003csub\u003e2\u003c/sub\u003e CT interactions,\u0026nbsp;as observed for a related compound\u003csup\u003e20\u003c/sup\u003e. However, after UV irradiation, paramagnetic\u0026nbsp;behaviour is observed\u0026nbsp;with large hysteresis between\u0026nbsp;the\u0026nbsp;zero-field cooling (ZFC) and field-cooling (FC) processes (Figs. 4b\u0026ndash;e). Note that the susceptibility\u0026nbsp;\u003cem\u003ec\u003c/em\u003e is negative,\u0026nbsp;in contrast\u0026nbsp;to\u0026nbsp;the\u0026nbsp;standard paramagnetism (\u003cem\u003ec\u003c/em\u003e \u0026gt; 0)\u003csup\u003e36\u003c/sup\u003e. This magnetic susceptibility can be explained if the unpaired electrons occupy significantly high energy levels with large orbital angular momenta. Such\u0026nbsp;a\u0026nbsp;situation is possible in the excited states caused by the Au 4\u003cem\u003ef\u003c/em\u003e\u0026ndash;Au n\u003cem\u003ef\u003c/em\u003e and Au 4\u003cem\u003ed\u003c/em\u003e\u0026ndash;Au n\u003cem\u003ed\u003c/em\u003e transitions (4 \u0026lt; n).\u0026nbsp;This\u0026nbsp;result\u0026nbsp;is consistent with the\u0026nbsp;above\u0026nbsp;discussion\u0026nbsp;of\u0026nbsp;XPS, indicating that we\u0026nbsp;observed\u0026nbsp;how\u0026nbsp;the\u0026nbsp;spins\u0026nbsp;polarized.\u0026nbsp;Additionally, alternating\u0026nbsp;increases\u0026nbsp;and\u0026nbsp;decreases\u0026nbsp;in the hysteresis\u0026nbsp;occur\u0026nbsp;between FC and ZFC (Figs. 4b\u0026ndash;e). The observed period (~30 h) depends on the time interval of the measurements and should be independent of\u0026nbsp;the\u0026nbsp;intrinsic oscillation periods of the spin system. However,\u0026nbsp;this characteristic\u0026nbsp;still demonstrates that the spin system\u0026nbsp;fluctuates\u0026nbsp;significantly\u0026nbsp;during the relaxation processes after\u0026nbsp;the\u0026nbsp;cessation of UV irradiation.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis\u0026nbsp;work\u0026nbsp;supports\u0026nbsp;the analysis of physical\u0026nbsp;and\u0026nbsp;chemical processes in time-resolved spectroscopy\u003csup\u003e37,38\u003c/sup\u003e. Different (meta)stable states are separated by an energy barrier, preventing spontaneous transitions between states.\u0026nbsp;Consistently, in this work, some of the atomic orbitals spontaneously\u0026nbsp;destabilized\u0026nbsp;themselves (Fig. 2d) with\u0026nbsp;alternating stabilization and destabilization\u0026nbsp;after\u0026nbsp;the\u0026nbsp;cessation of photoexcitation,\u0026nbsp;whereas\u0026nbsp;the total (Gibbs) energy of the system\u0026nbsp;decreased\u0026nbsp;during\u0026nbsp;these\u0026nbsp;processes. Because the chemical species in the system do not simultaneously behave in the same\u0026nbsp;manner, one transiently observes\u0026nbsp;the\u0026nbsp;averaged structure,\u0026nbsp;properties, and energy of different species as a snapshot of fluctuation. The XPS spectra also indicate that the core electrons cooperate to achieve a new stable state by exchanging their energies with each other and with\u0026nbsp;their\u0026nbsp;surroundings using their spin, charge, and orbital degrees of freedom. The observed\u0026nbsp;structural\u0026nbsp;and property changes should include\u0026nbsp;the\u0026nbsp;general aspects of chemical and physical changes. For example, in the material design and discussion\u0026nbsp;of\u0026nbsp;the mechanisms of electro-\u003csup\u003e39\u003c/sup\u003e and photoluminescence\u003csup\u003e40\u003c/sup\u003e and solar cells\u003csup\u003e41\u003c/sup\u003e, a few characteristic MOs around the valence bands/orbitals of key compounds are usually paid\u0026nbsp;the most\u0026nbsp;attention. The gradual and persistent changes in the closed-shell core electrons observed in this work contrast\u0026nbsp;sharply\u0026nbsp;with the rule of thumb that valence electrons dominate chemistry. All atomic orbitals cooperate to\u0026nbsp;rearrange\u0026nbsp;their chemical\u0026nbsp;bonds\u0026nbsp;for relaxation in response to large\u0026nbsp;perturbations, such as\u0026nbsp;photoexcitation and chemical reactions.\u003c/p\u003e\n\u003cp\u003eDuring slow structural changes after UV excitation, the valence and inner-shell electrons cooperate to polarize their spins and charges by exchanging their energies with each other and with their surroundings using the available degrees of freedom. This behaviour can be macroscopically observed as fluctuations in structure, properties, and energy. Based on the orbital approximation, by gradually and continuously adjusting the energy levels and spin states, the atomic orbitals at deeper levels possessing larger degrees of freedom can play dominant roles in stabilizing both the transient and final states during molecular orbital reconstruction. Some atomic orbitals had energy levels higher than their initial states after spontaneous changes. These findings provide an experimental basis for the currently proposed or assumed mechanisms of chemical reactions, photoexcitation, and other non-equilibrium phenomena to provide a deeper understanding of material dynamics.\u003c/p\u003e"},{"header":"Online content","content":"\u003cp\u003eAll methods, additional references, Nature Portfolio reporting summaries, source data, extended data, supplementary information, acknowledgements, peer review information, details of author contributions, competing interests, and statements of data and code availability are available at https://doi.org/.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePettine, J., et al. 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Chem. Phys.\u003c/em\u003e \u003cstrong\u003e26\u003c/strong\u003e, 3711\u0026ndash;3754 (2024) (DOI 10.1039/d3cp03214k)\u003c/li\u003e\n\u003cli\u003eHern\u0026aacute;ndez-Castillo, D., Eder, I. \u0026amp; Gonz\u0026aacute;lez, L. Guidelines to calculate non-radiative deactivation mechanisms of ruthenium tris(bipyridine) derivatives. \u003cem\u003eCoord. Chem. Rev.\u003c/em\u003e \u003cstrong\u003e510\u003c/strong\u003e, 215819 (2024) (DOI 10.1016/j.ccr.2024.215819)\u003c/li\u003e\n\u003cli\u003eKim, D., Yun, T., An, S. \u0026amp; Lee, C.-L. How to improve the structural stabilities of halide perovskite quantum dots: Review of various strategies to enhance the structural stabilities of halide perovskite quantum dots. \u003cem\u003eNano Converg.\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 4 (2024) (DOI 10.1186/s40580-024-00412-x)\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eSynthesis\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;procedures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe starting materials, MV\u0026middot;I\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e42\u003c/sup\u003e and TBA[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e43\u003c/sup\u003e, were prepared\u0026nbsp;following\u0026nbsp;the literature. Acetonitrile (FUJIFILM Wako Pure Chemical Corporation, super-dehydrated for organic synthesis) was\u0026nbsp;procured\u0026nbsp;and used without further purification. Single crystals of MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e were\u0026nbsp;synthesized using a\u0026nbsp;slow metathesis\u0026nbsp;approach\u0026nbsp;called the\u0026nbsp;\u0026lsquo;diffusion\u0026nbsp;method\u0026rsquo;.\u0026nbsp;MV\u0026middot;I\u003csub\u003e2\u003c/sub\u003e (1,1\u0026apos;-dimethyl-4,4\u0026apos;-bipyridinium diiodide; 1.32 mg, 3.0 mmol) and TBA[Au(dmit)\u003csub\u003e2\u003c/sub\u003e] (tetrabutylammonium bis(1,3-dithiole-2-thione-4,5-dithiolato)aurate(III); 5.41 mg, 6.5 mmol) were precipitated in CH\u003csub\u003e3\u003c/sub\u003eCN (90 mL) in separate compartments of a three-compartment H-tube with fine porous glass frits (No. 3) in a N\u003csub\u003e2\u003c/sub\u003e atmosphere under dark conditions at 296 K. The two reactants were allowed to dissolve slowly in the solvent, diffuse, and react.\u0026nbsp;After\u0026nbsp;~2\u0026ndash;3 weeks, black diamond-shaped platelets ~0.5-1 mm in size (b-MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e) were obtained,\u0026nbsp;along with\u0026nbsp;an\u0026nbsp;a\u0026nbsp;polymorph of black hexagonal platelets ~0.5-1 mm in size (a-MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e). The\u0026nbsp;a-type salt did not exhibit similar physical and structural properties after UV\u0026nbsp;irradiation.\u0026nbsp;Therefore,\u0026nbsp;this paper only\u0026nbsp;refers\u0026nbsp;to the\u0026nbsp;b-type salt without specifying the type. The UV\u0026ndash;vis absorption spectra of MV\u0026middot;I\u003csub\u003e2\u003c/sub\u003e, TBA[Au(dmit)\u003csub\u003e2\u003c/sub\u003e], and MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e are shown in Supplementary Fig. 1. The UV\u0026ndash;vis\u0026ndash;NIR spectra in the solution and solid state (powder) were recorded using a JASCO V-630 in transmittance mode at 295 K. MV\u0026middot;I\u003csub\u003e2\u003c/sub\u003e and TBA[Au(dmit)\u003csub\u003e2\u003c/sub\u003e] were dissolved in CH\u003csub\u003e3\u003c/sub\u003eCN (1.92\u0026nbsp;\u0026acute;\u0026nbsp;10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e5\u003c/sup\u003e M) and CH\u003csub\u003e3\u003c/sub\u003eOH (2.06\u0026nbsp;\u0026acute;\u0026nbsp;10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e5\u003c/sup\u003e M), respectively, and the baseline (the absorption by the quartz cell and solvent) was independently recorded and subtracted from each spectrum. The measurement conditions were as follows: data response = fast, scan rate = 200 nm min\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e, and data interval = 2 nm. The single crystals of MV\u0026middot;I\u003csub\u003e2\u003c/sub\u003e and MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e were separately well ground with Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (white fused alumina, 3000 mesh, Fujimi Incorporated) in an agate mortar, sandwiched between optical quartz plates, and subjected to spectrum measurement. The background (the quartz plates and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e powder) was independently recorded and subtracted from the sample spectra. TBA[Au(dmit)\u003csub\u003e2\u003c/sub\u003e] was finely powdered in an agate mortar without Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, sandwiched between the quartz plates, and subjected to spectrum measurement under identical measurement conditions. The background (the quartz plates) was independently recorded and subtracted from the sample spectra.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eUV irradiation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSingle-crystal X-ray structural analyses were\u0026nbsp;performed\u0026nbsp;under different UV irradiation conditions (light\u0026nbsp;source, bandpass filter, mirror\u0026nbsp;module, light\u0026nbsp;intensity, and irradiation duration). The\u0026nbsp;photoresponses\u0026nbsp;did not qualitatively\u0026nbsp;change\u0026nbsp;when the irradiation wavelengths were in the\u0026nbsp;range of\u0026nbsp;~240\u0026ndash;500 nm. This observation is consistent with the solid-state absorption spectra of MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e and related materials (SupplementaryFig. 1),\u0026nbsp;which show\u0026nbsp;main absorption peaks in this region.\u003c/p\u003e\n\u003cp\u003eTwo UV light sources were used in this study: a SUPERCURE-203S (200 W, Hg/Xe lamp, SAN-EI ELECTRIC, 220\u0026ndash;1,100 nm) for\u0026nbsp;the\u0026nbsp;XAFS and XPS analyses and MAX-350 (300 W, Xe lamp, ASAHI SPECTRA, 250\u0026ndash;1,050 nm) for the single-crystal X-ray structural analyses.\u0026nbsp;For\u0026nbsp;X-ray structural analysis, which\u0026nbsp;requires intense light to deeply penetrate single crystals, the\u0026nbsp;more powerful\u0026nbsp;MAX-350 light source was chosen. Both light sources were equipped with input power adjusters, multimode optical quartz\u0026nbsp;fibres\u0026nbsp;(core diameter: 5 mm, length: 1 m),\u0026nbsp;bandpass\u0026nbsp;filters, and mirror modules to select the output wavelengths and adjust the light intensities. The\u0026nbsp;distance\u0026nbsp;between the single-crystal sample and the optical\u0026nbsp;fibre\u0026nbsp;end\u0026nbsp;was\u0026nbsp;~13 mm for both XAFS and\u0026nbsp;the\u0026nbsp;single-crystal X-ray structural analyses. The light intensity at the sample position was estimated using a Si-diode power metre (NOVA, OPHIR); the\u0026nbsp;specifications of the light sources were provided by the suppliers. The wavelengths used were 250\u0026ndash;450 nm for XAFS and 300\u0026ndash;600 nm for the single-crystal X-ray structural analyses. The intensities were maintained constant through different measurement runs at ~1\u0026nbsp;W cm\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e2\u003c/sup\u003e for both XAFS and single-crystal X-ray structural analyses.\u0026nbsp;The sample temperature\u0026nbsp;during\u0026nbsp;the\u0026nbsp;UV irradiation\u0026nbsp;was\u0026nbsp;not corrected. Other details of\u0026nbsp;the\u0026nbsp;UV irradiation\u0026nbsp;have been\u0026nbsp;described in our previous paper.\u003csup\u003e20,44\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSingle-crystal X-ray structural analyses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePrior to performing X-ray structural analysis and physical property/spectroscopic measurements (electrical resistivity, magnetic susceptibility, XPS, and XAFS) on\u0026nbsp;the\u0026nbsp;new sample, the crystallinity was examined\u0026nbsp;using\u0026nbsp;X-ray oscillation photographs obtained using\u0026nbsp;a\u0026nbsp;VariMax RAPID/a\u0026nbsp;at the Advanced Research Support Centre (ADRES), Ehime University. High-quality single crystals (accuracy\u0026nbsp;\u0026sup3;90%) were first\u0026nbsp;analysed\u0026nbsp;at 298 K in the dark to confirm their initial\u0026nbsp;structures\u0026nbsp;before UV irradiation. Data were collected at ADRES using a Rigaku VariMax Saturn CCD724/a\u0026nbsp;detector equipped with a Mo rotor anode (\u003cem\u003el\u003c/em\u003e = 0.71073 \u0026Aring;). For each single crystal, X-ray oscillation photographs (1,440\u0026mdash;2,880 frames) were collected, a process that generally\u0026nbsp;requires\u0026nbsp;2\u0026ndash;4 h per crystal.\u003c/p\u003e\n\u003cp\u003eThe structural analysis temperature was carefully chosen by considering the relaxation rates from the UV-excited states and the thermal motion of atoms, both of which can depend on temperature. Lower temperatures are advantageous for observing crystal structures due to reduced thermal motion.\u003csup\u003e45\u003c/sup\u003e However, relaxation at extremely low temperatures, such as 77 K, was expected to be too slow to monitor until complete relaxation, based on ESR experiments conducted on a related material.\u003csup\u003e20\u003c/sup\u003e Considering the possible temperature increase under UV irradiation, the initial temperature for data collection was tentatively set to 128 K. For data collection at 128 K, the samples were cooled to 128 K at\u0026nbsp;a\u0026nbsp;rate of\u0026nbsp;-1 K min\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e under dark\u0026nbsp;conditions\u0026nbsp;to avoid unnecessary disorder, inhomogeneity, or possible supercooling. After 10 hours, corresponding to the initial rapid relaxation period estimated from the behaviour of related materials, the samples were warmed to 298 K at a rate of +1 K min\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e.\u003csup\u003e20\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eFor structural\u0026nbsp;analysis\u0026nbsp;during relaxation,\u0026nbsp;a\u0026nbsp;single crystal was first exposed to UV\u0026nbsp;radiation\u0026nbsp;for 5 min. The crystal was\u0026nbsp;then\u0026nbsp;maintained at 128 K\u0026nbsp;for\u0026nbsp;10 h\u0026nbsp;following\u0026nbsp;the cessation of UV irradiation. After 10 h, the crystal was stored at 298 K, except during the data collection at 128 K.\u0026nbsp;The\u0026nbsp;temperature variation rates were 1 K min\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e between 128 K and 298 K.\u0026nbsp;All\u0026nbsp;single-crystal X-ray structural analyses\u0026nbsp;were performed\u0026nbsp;at 128 K, and all\u0026nbsp;structures were based on the same single crystal. The structure during UV\u0026nbsp;irradiation could be completely solved with (~0.2%) or without\u0026nbsp;non-planar-coordinated\u0026nbsp;Au atoms (structures Au2 and Au3) with equal reliability.\u0026nbsp;Therefore,\u0026nbsp;the structure under UV\u0026nbsp;irradiation\u0026nbsp;is not discussed in detail.\u003c/p\u003e\n\u003cp\u003eRegardless of whether the crystal was exposed to UV irradiation, 18 frames of oscillation photographs were taken\u0026nbsp;at both\u0026nbsp;the\u0026nbsp;beginning and end of each data collection run\u0026nbsp;to detect any artefacts such as (partial) decomposition, microcracks, and other types of deterioration of the crystal caused by temperature variation or UV irradiation. The collected data were first processed using CrysAlisPro ver.41_64.93a (Rigaku) and then\u0026nbsp;analysed\u0026nbsp;using Olex 2.\u003csup\u003e46\u003c/sup\u003e The details of data collection, data processing, and structural analyses, which mainly consisted of standard procedures, are summarized in crystal information format (cif) files deposited to The Cambridge Crystallographic Data Centre (SupplementaryTable 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eXAFS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe X-ray absorption spectra were obtained using beamline 15A1 at the Photon Factory of the High Energy Accelerator Research Organization.\u0026nbsp;X-rays from the 2.5 GeV storage ring were monochromatized using a Si(111) double crystal. The spectra were recorded at ambient temperature and pressure. The samples were single crystals of MV[Au(dmit)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e,\u0026nbsp;freshly prepared, stored\u0026nbsp;in\u0026nbsp;the dark, and examined by single-crystal X-ray structural analyses\u0026nbsp;to confirm\u0026nbsp;they were high-quality single crystals\u0026nbsp;without\u0026nbsp;non-planar\u0026nbsp;coordinated\u0026nbsp;Au atoms.\u0026nbsp;Controlling\u0026nbsp;the thickness of the single crystals\u0026nbsp;was not possible, leading\u0026nbsp;to\u0026nbsp;variations between crystals that\u0026nbsp;significantly affected the signal-to-background ratio in\u0026nbsp;both XAFS\u0026nbsp;detection\u0026nbsp;modes\u0026nbsp;(fluorescence\u0026nbsp;and\u0026nbsp;transmittance). The spectra were\u0026nbsp;expected\u0026nbsp;to depend on the beam positions on the crystal surface because of possible inhomogeneity during and after UV irradiation. Accordingly,\u0026nbsp;micro-XAFS was\u0026nbsp;performed\u0026nbsp;using\u0026nbsp;a\u0026nbsp;beam size of 17\u0026nbsp;mm\u0026nbsp;(horizontal)\u0026times;32\u0026nbsp;mm\u0026nbsp;(vertical) mm\u003csup\u003e2\u003c/sup\u003e. The X-ray beam (~12 keV) was incident upon the most developed faces (the \u003cem\u003eab\u003c/em\u003e planes) of the diamond-shaped crystals\u0026nbsp;at an\u0026nbsp;incident angle of 45\u0026deg;,\u0026nbsp;to detect both\u0026nbsp;the\u0026nbsp;fluorescence and transmitted X-rays simultaneously using a\u0026nbsp;custom-built\u0026nbsp;Lytle detector and\u0026nbsp;an\u0026nbsp;ion chamber, respectively. The spectra of three single crystals in each salt (~0.4\u0026times;0.3\u0026times;\u003cem\u003ed\u003c/em\u003e mm\u003csup\u003e3\u003c/sup\u003e in dimension: \u003cem\u003ed\u003c/em\u003e = 0.008\u0026ndash;0.07 mm) were recorded to examine sample\u0026nbsp;dependence and reproducibility. Every time\u0026nbsp;a\u0026nbsp;single crystal was set in the holder,\u0026nbsp;a\u0026nbsp;2D map of\u0026nbsp;the\u0026nbsp;fluorescence/transmission intensity was collected by raster scanning the sample with a 20\u0026nbsp;mm step. The Au \u003cem\u003eL\u003c/em\u003e\u003csub\u003eIII\u003c/sub\u003e absorption edge energy was calibrated\u0026nbsp;using\u0026nbsp;Au foil.\u0026nbsp;While aligning the polarization angles of the incident X-rays along and perpendicular to the molecular planes of\u0026nbsp;Au(dmit)\u003csub\u003e2\u003c/sub\u003e could detect the deviated Au atoms most sensitively, no such polarization angle existed due to the different stacking directions of\u0026nbsp;Au(dmit)\u003csub\u003e2\u003c/sub\u003e columns in the unit cell. Preliminary\u0026nbsp;spectra\u0026nbsp;obtained\u0026nbsp;with\u0026nbsp;the polarization\u0026nbsp;angles of\u0026nbsp;the\u0026nbsp;// and\u0026nbsp;^\u0026nbsp;\u003cem\u003eb\u003c/em\u003e-axis in the \u003cem\u003eab\u003c/em\u003e plane exhibited\u0026nbsp;only\u0026nbsp;minor differences; hence,\u0026nbsp;polarization\u0026nbsp;dependence was not examined\u0026nbsp;further. Initially, the\u0026nbsp;\u0026lsquo;dark\u0026rsquo;\u0026nbsp;spectra were obtained\u0026nbsp;as described.\u0026nbsp;Next, the same sample was continuously exposed to UV\u0026nbsp;light,\u0026nbsp;during which the spectra were collected. The distance between\u0026nbsp;the\u0026nbsp;sample and the end of the light guide was 10 mm.\u0026nbsp;To confirm the UV-irradiation time and sample dependencies of XAFS, we recorded spectra using different crystals under the same conditions, except for the UV-irradiation time (5 min). The obtained spectra quantitatively agreed with each other. Immediately after the cessation of UV irradiation (\u003cem\u003et\u003c/em\u003e = 0 min), the spectra were repeatedly collected under the same\u0026nbsp;conditions. Each spectrum was\u0026nbsp;the average\u0026nbsp;of 5\u0026ndash;10 recordings, each\u0026nbsp;taking 15\u0026ndash;30\u0026nbsp;min. The spectra did not change after being repeatedly recorded at the same position\u0026nbsp;on\u0026nbsp;the crystal within this time. However, the XAFS spectra\u0026nbsp;change\u0026nbsp;irreversibly after prolonged\u0026nbsp;(\u0026sup3;45 min) synchrotron X-ray irradiation\u0026nbsp;at\u0026nbsp;~12 keV.\u0026nbsp;We collected several\u0026nbsp;XAFS spectra at different positions\u0026nbsp;on\u0026nbsp;the same sample to confirm reproducibility and homogeneity.\u0026nbsp;The samples used in the XAFS analysis were checked afterwards by single-crystal X-ray structural analyses to confirm that they retained their original structure and crystal quality without decomposition or deterioration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eXPS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXPS spectra were recorded using the single crystals covering a conducting\u0026nbsp;C\u0026nbsp;tape (~1.5\u0026nbsp;\u0026acute;\u0026nbsp;1.5 mm\u003csup\u003e2\u003c/sup\u003e, Nisshin EM) and a spectrometer JEOL JPS 9200 (Mg \u003cem\u003eK\u003c/em\u003ea\u0026nbsp;(1,253.6 eV, 12 kV, 40 mA)). The base pressure in the main chamber was ~6.6\u0026nbsp;\u0026acute;\u0026nbsp;10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e7\u003c/sup\u003e and ~7.8\u0026nbsp;\u0026acute;\u0026nbsp;10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e6\u003c/sup\u003e Pa\u0026nbsp;with and\u0026nbsp;without X-ray irradiation, respectively. The charge-up effects on the\u0026nbsp;BE\u0026nbsp;were corrected using the C 1\u003cem\u003es\u003c/em\u003e peak of the\u0026nbsp;C\u0026nbsp;tape (graphite). An electrostatic objective lens was used,\u0026nbsp;whereas\u0026nbsp;a magnetic objective lens was not. The field\u0026nbsp;of\u0026nbsp;view was 3.0 mm. We examined the Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e, Au 4\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e, Au 4\u003cem\u003ef\u003c/em\u003e\u003csub\u003e7/2\u003c/sub\u003e, Au 5\u003cem\u003es\u003c/em\u003e, S 2\u003cem\u003es\u003c/em\u003e, S 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e, and S 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e spectral regions at ~298 K.\u0026nbsp;First, the\u0026nbsp;stabilities\u0026nbsp;of the\u0026nbsp;samples\u0026nbsp;under continuous X-ray irradiation were examined. The spectra\u0026nbsp;remain\u0026nbsp;unchanged\u0026nbsp;after\u0026nbsp;several months of\u0026nbsp;continuous X-ray irradiation. The best measurement conditions were determined\u0026nbsp;to be in\u0026nbsp;the dark (Extended Data Table 1).\u0026nbsp;The S 2\u003cem\u003ep\u003c/em\u003e1/2 and S 2\u003cem\u003ep\u003c/em\u003e 3/2 peaks could not be resolved as separate peaks because the energy difference between them is smaller than the spectrometer\u0026apos;s resolution (~0.9 eV), resulting in the observation of a single merged peak.\u0026nbsp;The\u0026nbsp;sample was\u0026nbsp;then removed from\u0026nbsp;the spectrometer\u0026nbsp;and\u0026nbsp;exposed to UV irradiation in air for 5 min using the Hg/Xe\u0026nbsp;lamp described above (200 W, the range of 250\u0026mdash;450 nm was selected using a\u0026nbsp;bandpass\u0026nbsp;filter and an\u0026nbsp;Al\u0026nbsp;mirror). The distance between the end of the optical\u0026nbsp;fibre\u0026nbsp;and the sample was ~1 cm. For comparison, we performed XPS on an independently prepared sample of the same material under dark\u0026nbsp;conditions, and we then exposed the sample (in the main chamber) to UV\u0026nbsp;light\u0026nbsp;from the same light source through the quartz window of the main chamber, during which we\u0026nbsp;conducted\u0026nbsp;XPS\u0026nbsp;under UV irradiation (~1 h). The distance between the sample and the end of the optical\u0026nbsp;fibre\u0026nbsp;was ~30 cm. The XPS spectra after cessation of UV\u0026nbsp;irradiation were consistent between the two UV\u0026nbsp;irradiation conditions,\u0026nbsp;demonstrating that\u0026nbsp;the results\u0026nbsp;were\u0026nbsp;qualitatively independent of\u0026nbsp;the\u0026nbsp;UV\u0026nbsp;irradiation conditions.\u0026nbsp;Because\u0026nbsp;Ar\u0026nbsp;sputtering irreversibly\u0026nbsp;changes\u0026nbsp;the spectra with poor reproducibility, the sample surface was not etched prior to collecting the XPS spectra presented in this paper. Recording the series of spectra required ~1 h. The obtained spectra\u0026nbsp;were\u0026nbsp;distinguished by the elapsed time \u003cem\u003et\u003c/em\u003e (h)\u0026nbsp;after\u0026nbsp;the cessation of UV\u0026nbsp;irradiation, which\u0026nbsp;was defined as\u0026nbsp;the time\u0026nbsp;at which\u0026nbsp;we began collecting every series of XPS\u0026nbsp;spectra. The\u0026nbsp;spectrum\u0026nbsp;at \u003cem\u003et\u003c/em\u003e = 0 (h)\u0026nbsp;was\u0026nbsp;obtained during UV irradiation. The XPS\u0026nbsp;spectra\u0026nbsp;were\u0026nbsp;continuously recorded until \u003cem\u003et\u003c/em\u003e = 300 h, after which spectra were collected every 24 h until \u003cem\u003et\u003c/em\u003e = 3,000 h. The obtained spectra were\u0026nbsp;analysed\u0026nbsp;by curve\u0026nbsp;fitting using SpecSurf ver. 1.9.2.12 (2012, JEOL Ltd.) to obtain the\u0026nbsp;BEs\u0026nbsp;and intensities. The intensity\u0026nbsp;is\u0026nbsp;the peak area derived from the photoelectron counts (cps) multiplied\u0026nbsp;times\u0026nbsp;the acquisition time (s) and integrated along the BE (eV) across the peak widths.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhysical property measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eElectrical\u0026nbsp;resistivity was measured\u0026nbsp;at\u0026nbsp;296 K\u0026nbsp;using crystals, a\u0026nbsp;custom-built\u0026nbsp;cryostat, and\u0026nbsp;the\u0026nbsp;standard two-probe method with\u0026nbsp;a\u0026nbsp;constant direct current. Magnetic\u0026nbsp;susceptibility was\u0026nbsp;assessed\u0026nbsp;using polycrystalline samples\u0026nbsp;with\u0026nbsp;a magnetic property measurement system MPMS-XL7 (Quantum Design).\u0026nbsp;Detailed methods for these measurements can be found in our previous publication.\u003csup\u003e20,43,47,48\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTheoretical calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDFT calculations (R\u003cem\u003ew\u003c/em\u003eB97XD/LanL2DZ(5d, 7f)) were performed using Gaussian 16\u003csup\u003e31\u003c/sup\u003e and GaussView 6.1.1.\u003csup\u003e49\u003c/sup\u003e To obtain the energies of\u0026nbsp;the\u0026nbsp;three structural types of Au(dmit)\u003csub\u003e2\u003c/sub\u003e anions in the solid\u0026nbsp;state,\u0026nbsp;X-ray molecular structures were\u0026nbsp;utilized without\u0026nbsp;structural\u0026nbsp;optimization.\u0026nbsp;The electronic energy and thermodynamic quantities were\u0026nbsp;calculated for\u0026nbsp;a\u0026nbsp;simplified\u0026nbsp;system containing only the Au(dmit)\u003csub\u003e2\u003c/sub\u003e anion and MV cation. To examine model\u0026nbsp;dependence,\u0026nbsp;we performed similar\u0026nbsp;calculations\u0026nbsp;using systems with one molecule\u0026nbsp;(MV or Au(dmit)\u003csub\u003e2\u003c/sub\u003e) and\u0026nbsp;two molecules\u0026nbsp;(MV\u0026ndash;Au(dmit)\u003csub\u003e2\u003c/sub\u003e or Au(dmit)\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Au(dmit)\u003csub\u003e2\u003c/sub\u003e).\u0026nbsp;The results indicated that the molecular systems\u0026nbsp;depicted\u0026nbsp;in Supplementary\u0026nbsp;Figs. 4a\u0026ndash;c were\u0026nbsp;more appropriate than the remaining models.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSource data (crystallographic information format (cif) files) for Figs. 1b\u0026ndash;d, 2a,\u0026nbsp;and\u0026nbsp;2c\u0026nbsp;as well as\u0026nbsp;Extended Data\u0026nbsp;Figs. 1\u0026ndash;4,\u0026nbsp;and\u0026nbsp;6\u0026nbsp;were\u0026nbsp;deposited\u0026nbsp;at the\u0026nbsp;Cambridge Crystallographic Data Centre,\u0026nbsp;with the registry numbers\u0026nbsp;summarized\u0026nbsp;in Supplementary Table 2.\u0026nbsp;The\u0026nbsp;data\u0026nbsp;were\u0026nbsp;obtained free of charge from The Cambridge Crystallographic Data Centre\u0026nbsp;at\u0026nbsp;www.ccdc.cam.ac.uk/data_request/cif.\u0026nbsp;The source\u0026nbsp;data for Figs. 2b\u0026ndash;e,\u0026nbsp;3a\u0026ndash;f, and 4a\u0026ndash;e as well as Extended Data\u0026nbsp;Figs.\u0026nbsp;5a\u0026ndash;f,\u0026nbsp;7a\u0026ndash;d, and\u0026nbsp;8a\u0026ndash;d\u0026nbsp;are provided with this paper\u0026nbsp;in the\u0026nbsp;Supplementary Information.\u003c/p\u003e\n\u003cp\u003e42.\u0026nbsp; \u0026nbsp;Naito, T., et al. Simultaneous control of carriers and localized spins with light in organic materials.\u003cem\u003e\u0026nbsp;Adv. Mater.\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 6153\u0026ndash;6157 (2012) (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1002/adma.201203153\" target=\"_blank\"\u003e10.1002/adma.201203153\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e43.\u0026nbsp; \u0026nbsp;Steimecke, G., Sieler, H.-J., Kirmse, R.\u0026nbsp;\u0026amp; Hoyer, E. 1.3-Dithiol-2-thion-4.5-dithiolat aus\u0026nbsp;Schwefelkohlenstoff und alkalimetall.\u0026nbsp;\u003cem\u003ePhosphorus Sulfur Relat. Elem.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 49\u0026ndash;55 (1979) (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1080/03086647808069922\" target=\"_blank\"\u003e10.1080/03086647808069922\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e44.\u0026nbsp; \u0026nbsp;Naito, T., et al. UV-vis-Induced vitrification of a molecular crystal. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 1663\u0026ndash;1670 (2007) (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1002/adfm.200600583\" target=\"_blank\"\u003e10.1002/adfm.200600583\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e45.\u0026nbsp; \u0026nbsp;Wright, J. D. Molecular motion in crystals\u0026rsquo; in \u003cem\u003eMolecular Crystals\u003c/em\u003e. 2\u003csup\u003end\u003c/sup\u003e ed, Chap. 5 74\u0026ndash;96 (Wiltshire: Cambridge University Press, 2024), GB\u003c/p\u003e\n\u003cp\u003e46.\u0026nbsp; \u0026nbsp;Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. \u0026amp; Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. \u003cem\u003eJ. Appl. Crystallogr.\u003c/em\u003e \u003cstrong\u003e42\u003c/strong\u003e, 339\u0026ndash;341 (2009) (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1107/S0021889808042726\" target=\"_blank\"\u003e10.1107/S0021889808042726\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e47.\u0026nbsp; \u0026nbsp;Naito, T., et al. Molecular photoconductor with simultaneously photocontrollable localized spins\u003cem\u003e. J. Am. Chem. Soc.\u003c/em\u003e \u003cstrong\u003e134\u003c/strong\u003e, 18656\u0026ndash;18666 (2012) (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1021/ja306260b\" target=\"_blank\"\u003e10.1021/ja306260b\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e48.\u0026nbsp; \u0026nbsp;Naito, T., Inabe, T., Niimi, H.\u0026nbsp;\u0026amp; Asakura, K. Light-induced transformation of molecular materials into devices. \u003cem\u003eAdv. Mater.\u003c/em\u003e\u003cstrong\u003e16\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003e\u003c/strong\u003e\u003cstrong\u003e1786\u003c/strong\u003e\u003cstrong\u003e\u0026ndash;\u003cstrong\u003e1790\u003c/strong\u003e (\u003cstrong\u003e2004\u003c/strong\u003e)\u003c/strong\u003e (DOI\u0026nbsp;\u003ca href=\"https://doi.org/10.1002/adma.200400308\" target=\"_blank\"\u003e10.1002/adma.200400308\u003c/a\u003e)\u003c/p\u003e\n\u003cp\u003e49. \u0026nbsp; Dennington, R., Keith, T. A. \u0026amp; Millam, J. M. GaussView. version 6.1.1 (Shawnee Mission KS: Semichem Inc., 2016)\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e The authors are grateful to T. Tsuneda at Hokkaido University for valuable\u0026nbsp;discussions regarding\u0026nbsp;the DFT calculations. The authors\u0026nbsp;would like to\u0026nbsp;thank S. Mori and R. Konishi at ADRES, Ehime University,\u0026nbsp;for their\u0026nbsp;single-crystal X-ray structural analyses,\u0026nbsp;experimental advice, assistance with troubleshooting of\u0026nbsp;the\u0026nbsp;hardware and software, and productive\u0026nbsp;discussions. The authors are grateful to K. Konishi for assistance and valuable advice in using the SQUID. They are also grateful to K. Asakura at\u0026nbsp;the\u0026nbsp;Institute for Catalysis, Hokkaido University,\u0026nbsp;for the valuable assistance\u0026nbsp;with the\u0026nbsp;XAFS experiments.\u0026nbsp;The\u0026nbsp;XAFS experiments were performed\u0026nbsp;with\u0026nbsp;the approval of the Photon Factory Program Advisory Committee (Proposal No. 2022G104). This work was partially funded by a Grant-in-Aid for Challenging Exploratory Research (18K19061) from the JSPS, the Iketani Science and Technology Foundation (ISTF; 0331005-A), the Research Grant Program of the Futaba Foundation, the Casio Science Promotion Foundation, an Ehime University Grant for Project for the Promotion of Industry/University Cooperation, and the Canon Foundation (Science and Technology that Achieve a Good Future).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e T.N. conceived and supervised the project, designed almost all experiments, confirmed the experimental results, checked the analyses, and wrote the paper. Under the instruction of T.N., Y.M. synthesized the compound,\u0026nbsp;including its single crystals;\u0026nbsp;S.S. performed preliminary studies on the single-crystal X-ray structural analyses and theoretical calculations;\u0026nbsp;M.N. and Y.N. performed the single-crystal X-ray structural analysis and the first-principles calculations;\u0026nbsp;K.M. recorded the XPS spectra; and\u0026nbsp;K.M. and M.N. measured the magnetic susceptibility. Y.T., Y.N., and T.N. collaborated to\u0026nbsp;obtain\u0026nbsp;the XAFS spectra. All\u0026nbsp;the\u0026nbsp;authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e The online version contains supplementary material available at https://doi.org/......\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials \u0026amp; Correspondence\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials\u0026nbsp;should be addressed to Toshio Naito ([email protected]).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReprints and permissions information\u003c/strong\u003e is available at http://www.nature.com/reprints.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4811531/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4811531/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Photoexcitation and the subsequent physical or chemical processes are often too rapid to capture using direct, real-time observation methods1-6. Current approaches rely mainly on time-resolved spectra derived from short-pulsed lasers with appropriate wavelengths and pulse widths for the target phenomena7-10, supplemented by some experimental techniques combined with theoretical simulations11-14. In contrast, if a material exhibits sufficiently slow changes after photoexcitation, its structures and physical properties can be directly observed and compared with theoretical and spectroscopic results. This article explores the magnetic and structural properties of a new material that displays slow relaxation from UV-excited states. The study demonstrates that both valence and inner-shell electrons are cooperatively photoexcited, transitioning to a new state influenced by spin, charge, and orbital degrees of freedom. Unlike traditional theoretical descriptions, which assume time-independent atomic orbitals as the basis for molecular orbitals, this research reveals that atomic orbitals are time-dependent during these processes. These findings offer a foundational understanding of the relaxation processes from photoexcited states and provide insights into general chemical reactions.","manuscriptTitle":"Direct observations of slow photo-induced structural and physical changes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-30 13:38:52","doi":"10.21203/rs.3.rs-4811531/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-chemistry","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commschem","sideBox":"Learn more about [Communications Chemistry](http://www.nature.com/commschem/)","snPcode":"","submissionUrl":"","title":"Communications Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4665d251-c365-480a-83d8-cb7365cb0001","owner":[],"postedDate":"September 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":36433177,"name":"Physical sciences/Physics/Chemical physics"},{"id":36433178,"name":"Physical sciences/Materials science/Condensed-matter physics/Magnetic properties and materials"}],"tags":[],"updatedAt":"2024-09-30T13:38:52+00:00","versionOfRecord":[],"versionCreatedAt":"2024-09-30 13:38:52","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4811531","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4811531","identity":"rs-4811531","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}