Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions

Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions | 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 Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions Lirong Guo, Rongchen Chu, Xinyu Hao, Yu Lei, Haibin Li, Dongge Ma, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3026923/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Feb, 2024 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Photocatalytic redox is an important method for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here we report that Ag 3 PO 4 nanoparticles (NPs) can efficiently catalyze intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable, and can be scaled up using sunlight. Mechanistic studies indicate that visible-light irradiation on Ag 3 PO 4 NPs generates holes with high oxidation power, which effectively oxidize styrene adsorbates into radical cations. In photoreduced NPs, the conduction band electron ( e CB − ) has low reduction power due to the delocalization among the Ag + -lattices, while the NP surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with e CB − . Anethole radical cation on the NP’s surfaces has a lifetime of several hours, 10 8 times longer than in the homogeneous systems. The reaction between an adsorbed styrene molecule and a radical cation, the rate-limiting step, is greatly accelerated. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight. Physical sciences/Chemistry/Photochemistry/Photocatalysis Physical sciences/Chemistry/Physical chemistry/Excited states Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Styrene radical cations, which are one electron (1e)-oxidation intermediates of styrenes, play important roles in the synthesis of complex functionalized molecules and cyclic moieties, particularly the [2+2] and [4+2] pericyclic products. To generate and make use of styrene radical cations, extensive efforts have been devoted for a long time. Compared to single electron oxidants such as Ce 4+ , 1 Fe 3+ , 2 and hypervalent iodine reagents, 3, 4 photocatalysts (PCs) generate highly oxidizing holes under sunlight irradiation and operate under mild conditions, making photocatalysis a green and sustainable strategy for radical cation-mediated reactions. 5-15 However, the PCs utilised for generating radical cations are primarily homogeneous organic compounds, particularly transition metal-coordination complexes 8-11 and π-conjugated molecules. 12-15 Meanwhile, the scope of the approaches is constrained by the short lifetime of radical cations (on a μs scale 16-22 ). In contrast, inorganic semiconductor PCs (isPCs), such as TiO 2 , CdS, Bi 2 MoO 6 , and Ag 3 PO 4 , have been widely employed for solar light harvesting applications including water splitting, organic pollutant degradation, and photoelectric conversion. 23 From a practical standpoint, they are generally considered stable, recyclable, inexpensive, and environmentally friendly, making them an ideal choice for use in photosynthesis. However, the efficiency of isPCs in the 1e-oxidative activation of non-polar and non-coordinative C=C moieties on their surfaces is typically low. 16, 19, 20, 24-31 One obstacle is the extremely short lifetime of holes (fs to ns 32 ), which significantly slows down the 1e-oxidation of the C=C moieties (Figure 1a). Moreover, even if some alkene radical cations are slowly generated at the surfaces of a traditional isPC like TiO 2 , they undergo few intermolecular C-C formation reactions. 16 Instead, they are more prone to nucleophilic attack by long-lived photogenerated electrons ( e CB − ), resulting in ineffective 1e-oxidation. These hindrances lead to a diminished quantum yield of light (i.e. reduced reaction rate) and low product yield, regardless of reaction time. Therefore, it is imperative to extend the lifespan of alkene radical cations for affordable and recyclable PCs that can effectively harvest sunlight for pericyclic reactions. However, this remains an ongoing challenge. Among all the available isPCs, Ag 3 PO 4 stands out as one of the few that exhibits an inherent visible-light response. 33 It has been extensively used in visible-light-driven water oxidation 33-35 and organic pollutant degradation. 35, 36 Compared to other commonly used semiconductors, it produces strong oxidizing holes and weak reducing electrons under visible-light irradiation (+2.9 V and +0.45 V vs. NHE; Figure 1b). Moreover, the surfaces of Ag 3 PO 4 are rich in large PO 4 3− anions with high-charge-density that can strongly electrostatically interact with cationic species such as radical cations. As a result, photo-excited Ag 3 PO 4 NPs may efficiently generate but inefficiently quench radical cations, allowing for the accumulation of radical cations to facilitate radical cation-mediated reactions. In this study, we demonstrate that Ag 3 PO 4 efficiently catalyse intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible light or solar irradiation. The system exhibit remarkable efficiency with respect to substrate scope, product yield, diastereoselectivity, apparent quantum yield (AQY), and scaleup synthesis under solar irradiation. Two critical aspects of the reaction mechanism are validated: (1) the existence of long-lived 1a •+ radical cation on the surfaces of Ag 3 PO 4 NPs that are photo-reduced in situ, (2) the acceleration of rate-limiting step by prolonging the lifetime of 1a •+ . To the best of our knowledge, this is the first report on employing an isPC for pericyclic reaction under visible-light irradiation. Our discoveries may pave the way for employing highly active organic radical cations and even radical anions in critical pericyclic processes. Results and Discussion Transformation of styrene 1a to trans -cyclobutane 2a Anethole ( 1a ) has been the most studied electron-rich β -substituted styrene in [2+2] cycloaddition reactions. 3, 18, 37 Therefore, it was selected as the model compound to evaluate the photocatalytic perfomance of Ag 3 PO 4 (Scheme 1). Although different Ag 3 PO 4 samples exhibited in distinct reaction rates, they hardly affected final product yields. Thus, a self-synthesized Ag 3 PO 4 sample coomposed of nanospheres with a diameter of 230 ± 60 nm was used for further studies (Figure 2a). The cycloaddition reaction was conducted under an N 2 atmosphere by irradiating a suspension of reactant 1a in hexafluoroisopropanol (HFIP) solvent containing a catalytic quantity of Ag 3 PO 4 (12 mol%) at 0 °C. No additive was introduced. The conversion of 1a proceeded smoothly, affording trans -cyclobutane 2a as the sole product (see Figure S1 for the time-resolved 1 H NMR spectra and kinetics). After 12 h of reaction, the yield of 2a reached 82%, indicating a highly diastereoselective process ( d.r. >19:1). Further irradiation did not affect conversion due to equilibration between 1a and 2a (Figure S2), as commonly observed in photocatalyzed radical cation processes. 37, 38 The control experiments demonstrate that in the absence of Ag 3 PO 4 or light at room temperature, or stirring the reaction mixture in the dark at 80 °C, no conversion of 1a occurs (see Table S1 for screening of the experimental conditions). Therefore, both light and Ag 3 PO 4 are indispensable for the reaction, excluding the possibility of a thermocatalytic mechanism. The AQY values were determined according to the initial 30-min yield. As shown in Figure 2b, Ag 3 PO 4 can effectively harvest visible light up to 500 nm to initiate the 1a→2a cycloaddition, which is close to its absorption edge. The action spectrum of AQY matches the UV-vis diffuse-reflectance spectrum of Ag 3 PO 4 . Although we were aware that depositing AgNPs on the surfaces of Ag 3 PO 4 could enhance its photo-absorption and charge-separation efficiency, 39 our experiments with the AgNPs-loaded sample, i.e., Ag/Ag 3 PO 4 , affording a substantially lower yield (optimum yield = 60% after 24 h). This suggests that AgNPs are not the photocatalyst. Therefore, it can be concluded that Ag 3 PO 4 is the true photocatalyst. Silver salt-based photocatalysts often suffer from photo-corrosion. 40-43 However, in the current system, the 12 mol% of initially added Ag 3 PO 4 successfully worked five consecutive photocatalytic cycles with only a slight decrease in efficiency (Figure 2c), resulting in a turnover number of 13. Photo-corrosion of Ag 3 PO 4 was observed as evidenced by its significant darkening after five cycles. The TEM image indicates the formation of numerous AgNPs on the surfaces of Ag 3 PO 4 (Figure S3). Nevertheless, regeneration of the recycled sample was achieved through a simple immersion in 6.7 mM Na 2 HPO 4 aqueous solution and addition a drop of 30% H 2 O 2 . 44 Within minutes, color, microscopic morphology, and photocatalytic performance were fully restored (Figure S3). As shown in Figure 2d, while other silver salts such as AgCl, AgBr, and AgI, exhibit activity, their 1a conversion and 2a selectivity are significantly lower than that of Ag 3 PO 4 . Furthermore, both AgCl and AgBr suffer from severe photo-corrosion. In comparison to the widely studied heterogeneous photocatalysts 45 including graphitic carbon nitride (g-C 3 N 4 ), Bi 2 MoO 6 , and TiO 2 , the performance of Ag 3 PO 4 is superior. For example, the reaction rate was notably low over TiO 2 even under UV. Furthermore, electron accumulation caused TiO 2 to exhibit blue hue and ultimately became completely inert once conversion reached 18% (Figure S4). Table S2 shows that Ag 3 PO 4 performs comparably to state-of-art PCs and single-electron oxidants such as Ru(bpm) 3 (BArF) 2 , 37 PhI(OAc) 2 3 and Fe(ClO 4 ) 3 in the 1a→2a cycloaddition. 18 Therefore, Ag 3 PO 4 is highly applicable for [2+2] cyclobutanation reactions. Ag 3 PO 4 /visible light system for pericyclic reactions Given the success of the [2+2] homo-cycloaddition of 1a , we sought to explore whether the Ag 3 PO 4 /visible light system could serve as a versatile tool for achieving various pericyclic reactions. Our initial focus was on investigating the scope of the intermolecular dimerization reaction. As shown in Figure 3, a diverse range of electron-rich styrenes with varying substituents underwent smooth reaction, affording the corresponding symmetrical cyclobutanes in moderate to good yields and excellent diastereoselectivity ( 2a - 2h , yield ranges 42%-83%, d.r. > 19:1). Electronic density of the aromatic ring and steric hindrance at β -site exert a noticeable influence on the reaction outcome ( 2b vs. 2c , 2a vs. 2d-2f ). However, this catalytic system exhibits high tolerance toward steric hindrance at the benzene ring ( 2a vs. 2f - 2h ). Notably, NO 2 -, OH-, and COOH-substituted styrenes were challenging substrates for other [2+2] cycloaddition catalytic systems, 46 as well as the current Ag 3 PO 4 system (Table S3). Finally, we achieved a 70% isolated yield of magnosalin ( 2h ), a valuable natural product. We then use the system to synthesize unsymmetric cyclobutanes and were pleased to discover that a variety of styrenes, including unsubstituted styrene ( 4a ) and substituted styrenes with electron-donating groups (EDGs; 4b , 4d, 4i ) and electron-withdrawing groups (EWGs; 4c, 4e, 4f, 4g, 4h ) at both ortho-, meta- and para-sites of the benzene rings, could be employed as model reaction counterparts using 1a . The sole byproduct resulting from these crossed reactions is the homo-cycloaddition product, e.g., 2a . However, because the crossed reactions are much faster than the homo-cycloaddition (see Figure S5 for a comparison of the rates), introducing 1a via a syringe pump would inhibit the homo [2+2] reaction. Next, we explored the feasibility of intramolecular [2+2] cycloaddition, an efficient approach for synthesizing fused heterocycles. 6 Strikingly, all tested bis(styrene)s afforded good to excellent yields of the desired cyclobutanes ( 6a - 6t ). The intramolecular [2+2] cycloadditions exhibit a broad tolerance toward EDGs, EWGs, and the steric hindrance at both the benzene ring and the β -site. The Diels-Alder reaction is considered one of the essential C-C bond-forming reactions in the synthetic organic chemistry. Recent studies have shown that photocatalytic methods are effective in the radical-cation-mediated cycloadditions of electron-rich olefins and dienes, 47-49 which are challenging substrates for conventional thermal processes. In this study, we found that even with a reduced Ag 3 PO 4 loading of 8 mol%, the Ag 3 PO 4 /visible light system was still capable of facilitating Diels-Alder cycloadditions -involving the radical cations. Moreover, the 8 mol% of Ag 3 PO 4 was successfully reused for five consecutive runs without any noticeable decrease in performance (Figure S6). Based on the substituted styrenes, the yields achieved in all tested reactions are near unity ( 8a - 8h ). The remarkable diastereoselectivity of the reactions is noteworthy. Specifically, nearly all intermolecular [2+2] products are trans ; intramolecular [2+2] products are predominately cis , and nearly all Diels-Alder reactions yield trans products. Scale synthesis of [2+2] and [4+2] reactions To investigate the synthetic potential of the Ag 3 PO 4 /visible light system, we performed large-scale [2+2] and [4+2] reactions under natural sunlight irradiation by placing the reaction flasks on a windowsill at ambient temperatures (1-10 °C). The sunlight intensity ranged from 15-23 mW cm -2 . Interestingly, 41.5 g of the [4+2] cycloaddition product 8a was obtained almost quantitatively in a one-pot reaction after only six hours of irradiation (Scheme 2). After being filtered through diatomite, the Ag 3 PO 4 solid was removed, resulting in nearly pure 8a (41.5 g), which confirms the method’s flexibility and ease of use. The intermolecular [2+2] homo-cycloaddition of 1a yielded a 60% yield of 2a (100% selectivity) before Ag 3 PO 4 (5 mol%) became deactivated. However, upon reintroduction of regenerated Ag 3 PO 4 into the catalytic system, a final yield of 80% of 2a was achieved (Scheme 2). Tables S4-S6 demonstrate the superior performance of the Ag 3 PO 4 /visible light system compared to the state-of-art reports in [2+2] and Diels-Alder cycloadditions. The current system boasts one of the highest efficiencies heterogeneous systems, with broad light absorption. It is the only one capable of realizing intramolecular and intermolecular 2+2 cycloadditions and Diels-Alder reactions. Mechanism study and DFT simulations Laser flash photolysis (LFP) was performed to detect the transient species involved in the photocatalytic 1a → 2a cycloaddition. The transmittance LFP spectra of a 1a /Ag 3 PO 4 /HFIP suspension are depicted in Figure 4a. The two distinct, intense peaks centered at ca. 387 and 605 nm precisely match the spectra of 1a •+ generated by photolysis of homogeneous solutions of 1a /H 2 O-MeCN at 266 nm 50 and 1a /MeCN at 308 nm, 51 respectively, as reported in previous studies. Figure 4b demonstrates that the absence of 1a or Ag 3 PO 4 resulted in no signal from a 355-nm laser pulse, indicating the indispensability of both 1a and Ag 3 PO 4 for the formation of 1a •+ . Hence, the LFP spectra confirm that photogenerated h + of Ag 3 PO 4 faciliates the 1e-oxidation of 1a to afford 1a •+ . The concentration of a transient species, which is determined by both formation rate and lifetime, is essential for detecting it via LFP. Hence, the observation of 1a •+ in the 1a /Ag 3 PO 4 /HFIP system suggests that 1a •+ forms rapidly and has a long life, allowing for its accumulation due to its formation far exceeding decay. Recall Figure 4a, the sample initially exhibited strong background absorption, which significantly decreased after 250 μs due to the sedimentation of Ag 3 PO 4 NPs. The spectra at 250 and 500 μs showed similar level of background absorption, indicating that sedimentation was minor during this time period. Based on this understanding, we measured the decay kinetics of 1a •+ in the 1a /Ag 3 PO 4 /HFIP suspension at λ = 600 nm. Figure 4c demonstrates that the signal intensity decayed significantly before 500 μs, which could be mostly attributable to the sedimentation mentioned above of Ag 3 PO 4 NPs. Afterward, the signal intensity remained nearly constant until 1900 μs, suggesting that the lifetime of 1a •+ in the 1a /Ag 3 PO 4 /HFIP system must be more than 1900 μs. We conducted light-on-off experiments to investigate the lifetime of 1a •+ in the 1a /Ag 3 PO 4 /HFIP system. The reaction vial was either left stirring in the dark after turning off the light or centrifuged to settle down the Ag 3 PO 4 NPs before being left in the dark. In the former situation, over the next six hours, there was a gradual increase of ca. 8% in yield of 2a (Figure 4d), indicating that 1a •+ could maintain its reactivity for many hours. This is distinct from the homogeneous systems, where the 1a → 2a cycloaddition practically ceased upon light-off. 52 In the dark reaction without agitation, the yield of 2a remained unchanged after Ag 3 PO 4 settled down (Figure 4d). It indicates that the long-lived 1a •+ radical cations must remain adsorbed on the surfaces of the reduced Ag 3 PO 4 NPs (denoted as (Ag 3 PO 4 ) n − , where n is the number of e CB − per NP). When all the Ag 3 PO 4 NPs settled down, the 1a molecules in solution could not reach 1a •+ , and thus the cycloaddition ceased. This further confirms that the radical cation-mediated [2+2] pericyclic reaction occurs on the surfaces of Ag 3 PO 4 rather than in the solution. It was reported that the decay rate constant 50, 53 of 1a •+ is 4 × 10 4 s -1 in aerated MeCN, corresponding to a very short lifetime of 25 μs. 51 This is likely why the 1a → 2a cycloaddition stopped nearly instantly upon light-off in homogeneous systems. 21, 52 To probe the lifetime of 1a •+ in neat HFIP, we used a 266-nm laser pulse to excite a 1a /HFIP solution. However, the system produced signals from unknown species and the absorption peaks of 1a •+ at ca. 387 and 605 nm were not detected. This may suggest that the lifetime of 1a •+ in HFIP is too short, resulting in a 1a •+ concentration below the detection limit. We also used a 355-nm laser pulse to excite the 1a /TiO 2 /HFIP system, which produced an 16% yield of 2a , indicating that photo-excited TiO 2 NPs generated 1a •+ . However, the transient spectrum of 1a •+ was not detected by LFP (Figure S7), implying that its lifetime in the system is also very short. We found that the adsorption of reactant 1a and desorption of product 2a are crucial in the reaction. Figure 5a shows that the adsorption of 1a on the (100)-facet-rich spherical Ag 3 PO 4 NPs (as the representative example) can fit well to the Langmuir type-I isotherm (eq 1), where Г is the adsorbed amount at the adsorption/desorption equilibrium concentration C eq . The Langmuir coefficient K and the capacity of adsorption Г m are calculated to be 5.8 ± 0.6 M −1 and 2.9 ± 0.1 mmol g −1 , respectively. In contrast, the adsorption of 2a on Ag 3 PO 4 surfaces is barely detectable, indicating very weak adsorption of 2a . At low 1a concentrations, the AQY values increase dramatically with the initially added concentration of 1a but then approach a plateau (Figure S8). This differs from a typical homogeneous bimolecular reaction, which is second order depending on the substrate concentration. Instead, the AQY values are well linearly correlated with the square of the fractional coverage of 1a , Ɵ (eq 2), where k denotes the slope of the plot (Figure 5b). This kinetic equation corroborates that the conversion of 1a through photocatalysis occurs on the Ag 3 PO 4 surface. The rate-limiting step (RLS) of the formation of 2a involves two molecular species of 1a adsorbed on the surface. We also observe a significant solvent effect in the performance of Ag 3 PO 4 in the 1a → 2a cycloaddition reaction (Figure 5c). Ag 3 PO 4 did not perform well in EtOAc, n -hexane or CH 2 Cl 2 , but performed better in CH 3 CN, MeNO 2 and TFE, and performed best in HFIP. Surprisingly, eq 2 applies to the results from different solvents. Thus, solvents influence the AQY by modulating the 1a distribution between the bulk solution and Ag 3 PO 4 surfaces. It has been reported that the facets of photocatalysts substantially influence their activities, especially in the case of Ag 3 PO 4 . 34, 35, 54, 55 For the 1a → 2a cycloaddition reaction, we used the spherical, rhombic dodecahedral, cubic, and tetrahedral NPs of Ag 3 PO 4 , which are rich in {100}, {110}, {100} and {111} facets, respectively, 34 . Figure 5d displays distinct AQYs on different facets and eq 2 is applicable to the results from various Ag 3 PO 4 facets. Overall, Figure 5 indicates that the photocatalytic cycloaddition reaction on Ag 3 PO 4 surfaces follows the Langmuir-Hinshelwood mechanism for a bimolecular reaction. It also implies that the interaction between 1a and Ag 3 PO 4 surfaces is vital in the success of Ag 3 PO 4 in the photocatalytic [2+2] cycloadditions. We conducted DFT simulations to determine the mechanism of interfacial interactions between 1a (and 2a ) and the Ag 3 PO 4 surfaces. As the (100) facet is the lowest-energy facet of Ag 3 PO 4 crystals 34, 35, 55 and the primary surface of spherical Ag 3 PO 4 NPs, we selected the PO 4 3− -terminated and the Ag + -terminated (100) facets to calculate the optimal adsorption configurations (see Figures S9-S10 for details of results). Figure 6 displays the lowest-energy configurations of 1a and 2a molecules on the PO 4 3− -terminated (100) facet. It should be noted that the size of PO 4 3− is much larger than that of Ag + (2.38 Å vs. 0.67 Å), but comparable to molecule 1a in size. Molecule 1a lies parallel to the facet, with its long axis aligned with the a -axis of the crystal lattice, and the CH=CH moiety positioned close to the O 2− ions of PO 4 3− . In this configuration, each 1a molecule intimately contacts four PO 4 3− anions, maximizing the interfacial interaction between 1a and the Ag 3 PO 4 surface. The strong interaction is consistent with the previously discussed adsorption of 1a to the Ag 3 PO 4 surfaces. This adsorption mode should be beneficial for the 1e-oxidation of the CH=CH moiety upon photo-excitation of Ag 3 PO 4 since photogenerated holes are localized at O of PO 4 3− . 56 The energy required for adsorption of each 1a molecule from the vacuum is −2.10 eV (Figure 6, ab). In contrast, the calculated energies for 1a adsorption onto PO 4 3− -terminated (100) facet along the b -axis and that onto the Ag + -terminated (100) facet along both the a - and b -axis, are substantially smaller at −1.67, −1.54, and −1.54 eV, respectively (Figures S9-S10). These lower adsorption energies can be attributed to the greater spacing between the adjacent PO 4 3− anions on these facets, which weakens the contact between 1a and PO 4 3− . However, due to the large steric effects of the 2a molecule, each 2a has an optimum adsorption energy of −1.56 eV when adsorbed on the PO 4 3− -terminated (100) facet (Figure 6, cd). The above calculations reveal a large adsorption energy difference between two 1a and one 2a , i.e., +2.64 eV on the PO 4 3− -terminated Ag 3 PO 4 (100) facet in a vacuum. The much weaker adsorption of 2a suggests that the 1a → 2a cycloaddition on the Ag 3 PO 4 surfaces benefits from the easier removal of product 2a . The atomic Bader charges shown in Figure 6e indicate that the electron density of 1a changes upon adsorption. The overall Bader charge of adsorbed 1a is 0.34e, indicating a transfer of 0.34e from 1a to the Ag 3 PO 4 surfaces during adsorption. The two H-atoms in the CH=CH moiety have enormous Bader charges, namely, 0.1323e and 0.1e, respectively. This, combined with the very negative Bader charge of the CH 3 O moiety (−0.4587e), strongly suggests that polarization occurs in molecule 1a and that its CH=CH group is activated upon adsorption. The high Bader charge also means that the CH=CH group is the most readily oxidized site in 1a . Figure 7 illustrates a plausible mechanism for Ag 3 PO 4 triggering the [2+2] cycloaddition of 1a under visible-light irradiation. Initially, Ag 3 PO 4 adsorbs 1a molecules on its surface via PO 4 3− anions (step I). Then, upon excitation, Ag 3 PO 4 generates many e CB − in the conduction band and h + in the valance band (step II). Due to the fact that the conduction band bottom is mainly composed of hybridized Ag 5s5p orbitals, 33 the reduction power of the electrons in the conduction band of Ag 3 PO 4 is low ( E CB = +0.45 V vs. NHE 33, 39, 57, 58 ). The unreactive e CB − remains in the form of (Ag δ+ ) m − , which means it is shared by many Ag + ions. The observed AgNP formation substantiates that e CB − transfers to Ag + ions. The valance band top of Ag 3 PO 4 mainly comprises hybridized O 2p and Ag 4d orbitals. The h + in the valence band has strong oxidation power ( E VB = +2.90 V vs. NHE 33, 39, 57, 58 ) and able to gain an electron from the CH=CH group of 1a to yield 1a •+ (step III). The 1e-oxidation of 1a results in the photocatalytically reduced NP with numerous e CB − . The 1a •+ species strongly adsorbs on the surfaces of (Ag 3 PO 4 ) n − . In this case, the electrostatic interaction between 1a •+ and (Ag 3 PO 4 ) n − NP surfaces is analogous to the interactions in homogeneous solutions described by Yoon et al for 1a •+ with a tetraarylborate anion, 17 Ishihara et al for 1a •+ with FeCl 4 − , 18-20 and List et al for 1a •+ with an imidodiphosphorimidate counteranion. 21 The adsorbed 1a •+ is stabilized by electrostatic interaction with the (Ag 3 PO 4 ) n − surfaces. The low possibility recombination between 1a •+ and e CB − shared by multiple Ag + cations, (Ag δ+ ) m − , is evidenced by the observation of AgNP formation. As a result, the lifetime of 1a •+ is dramatically prolonged to hours, which is over 10 8 times longer than in a homogeneous solution (μs level 51 ). The long lifetime of 1a •+ benefits the nucleophilic attack by another adsorbed 1a molecule, allowing the reaction of 1a + 1a •+ → 2a •+ in step IV to proceed (the RLS; see Supporting Information for analysis). The ability to generate the long-lived radical cation 1a •+ distinguishes (Ag 3 PO 4 ) n − from a traditional photocatalytically reduced TiO 2 NP. On the illuminated TiO 2 NP, the lifetime of 1a •+ was too short to detect, and the conversion was only 18% (Figure 2d). Okada et al used a substantial excess of TiO 2 (e.g., > 6 eq) to minimize the accumulated electron per NP and extra LiClO 4 (1.0 M) to stabilize the radical cations. 18 , 22-23 , 25-27 In contrast, Ag 3 PO 4 photocatalysis can harvest the visible spectrum of sunlight and achieve a high yield of the desired product without any additives. Conclusion Ag 3 PO 4 is a powerful photocatalyst for homo, crossed, intramolecular [2 + 2], and Diels-Alder [4 + 2] pericyclic reactions under visible-light irradiation. The catalytic process is mild, straightforward, affordable, additive-free, scalable under sunlight irradiation, and allows for easy product separation and catalyst reuse. It has a broad substrate scope and produces a wide range of desired products in modest to excellent yields. Our study reveals the potential of this photocatalytic process for fine chemical production. We have demonstrated that the rate-limiting step is the reaction between the reactant and its 1e-oxidation intermediate, a radical cation. The lifetime of anethole radical cation ( 1a •+ ) on the Ag 3 PO 4 surfaces reaches several hours, which is over 10 8 times longer than that in the homogeneous solutions, thus effectively promotes the rate-limiting step. The long lifetime of 1a •+ is attributed to the appropriate band structure of Ag 3 PO 4 and the strong electrostatic interaction between 1a •+ and the (Ag 3 PO 4 ) n − NP surfaces, which should be a general and essential mechanism for promoting chemical processes mediated by radical cations on heterogeneous surfaces. This may inspire new ideas for more challenging radical cation/anion-mediated solar synthesis using inorganic semiconductor photocatalysts. Methods General procedure for the photocatalytic reactions. The reactions were carried out in 10-mL Pyrex vials. Olefin and Ag 3 PO 4 were dispersed in a solvent in the vial, which was then purged for 10 min with high-purity N 2 (99.999%). The vial was immersed in a cryogenic reaction bath to maintain the reaction temperature. The reaction suspension was stirred in the dark for 30 min to achieve adsorption-desorption equilibrium. The mixture was then exposed to the lamp from the side. To monitor the reaction progress, a syringe was used to withdraw 10 µL of the solution for analysis by thin-layer chromatography (TLC). After the reaction, the suspension was centrifuged to separate the solid catalyst from the solution. The residue purified with column chromatography to afford the desired pure products. Details for the homo-dimerization of styrenes. To a solution of styrene 1 (1.0 mmol) in 3.0 mL of HFIP, Ag 3 PO 4 (12 mol%) was added in one portion. The remaining steps are the same as the general procedure. Details for the cross-dimerization of styrenes. To a solution of styrene 3 (1.0 mmol, 2.0 eq) in 2.0 mL of HFIP was added Ag 3 PO 4 (20 mol%). Then, the reaction mixture was degassed by purging with high-purity nitrogen for 10 min. An ice bath was used to maintain the reaction temperature. The mixture was stirred in the dark at 0 °C for half an hour to achieve adsorption-desorption equilibrium. The photocatalytic reaction was then initiated by irradiating the dispersion from the side with the LED lamps. During the reaction, a solution of styrene 1 (0.5 mmol) in 2.0 mL HFIP was added using a syringe pump (at a rate of 4.0 mL/h). The remaining steps are the same as the general procedure. Details for the intramolecular [2 + 2] reactions. To a solution of styrene 5 (0.3 mmol) in 2.0 mL of HFIP, Ag 3 PO 4 (10 mol%) was added in one portion. The remaining steps are the same as the general procedure. Details for the Diels–Alder cycloadditions. To a solution of the diene 7 (2.0 mmol, 2.0 eq) in 2.0 mL of HFIP was added Ag 3 PO 4 (8 mol%). Then, the reaction mixture was degassed by purging with high-purity nitrogen for 10 min. An ice bath was used to maintain the reaction temperature. The mixture was then stirred in the dark at 0 °C for half an hour to achieve adsorption-desorption equilibrium. The photocatalytic reaction was initiated by irradiating the dispersion from the side with an LED lamp. During the reaction, a solution of styrene 1 (1.0 mmol) in 2.0 mL of HFIP was added using a syringe pump (at a rate of 4.0 mL/h). The remaining steps are the same as the general procedure. Data availability The authors declare that all relevant data supporting the findings of this study are available either within the manuscript itself and/or in the Supplementary Information. Experimental details and characterization of products are provided in the Supplementary Information. All other data are available from the corresponding author upon request. Declarations Acknowledgments The authors gratefully acknowledge the National Natural Science Foundation of China (Grant Nos 22276112, 21922605, 22076007), the Natural Science Foundation of Shandong Province (Nos. 2019GSF109065, 2021CXGC011202 and ZR2019ZD45), the Taishan Scholar Project 454 Foundation of Shandong Province (No ts20190908) for the financial supports. Author contributions Y.W., C.H. conceived the idea and directed the project. L.G. performed the experiments and analyzed the data. R.C., X.H., Y.L., and H.L., D.M. participated in characterization studies. G.W. performed the DFT calculation. Y.W. and L.G. wrote the manuscript, and L.G. prepared the Supplementary Information. Competing interests The authors declare no competing interests. References Nair, V.,Rajan, R.,Mohanan, K. & Sheeba, V. Cerium(iv) ammonium nitrate-mediated oxidative rearrangement of cyclobutanes and oxetanes. Tetrahedron Lett. 44, 4585–4588 (2003). Yu, Y.,Fu, Y. & Zhong, F. 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Synthesis of Ag 3 PO 4 crystals with tunable shapes for facet-dependent optical property, photocatalytic activity, and electrical conductivity examinations. ACS Appl. Mater. Interfaces 9, 39086–39093 (2017). Ke, J. et al. Facet-dependent electrooxidation of propylene into propylene oxide over Ag 3 PO 4 crystals. Nat. Commun. 13, 932 (2022). Xiong, Y. et al. Single-atom Rh/N-doped carbon electrocatalyst for formic acid oxidation. Nat. Nanotechnol. 15, 390–397 (2020). Hou, Y. et al. Ag 3 PO 4 oxygen evolution photocatalyst employing synergistic action of ag/agbr nanoparticles and graphene sheets. J. Phys. Chem. C 116, 20132–20139 (2012). Bi, Y.,Ouyang, S.,Cao, J. & Ye, J. Facile synthesis of rhombic dodecahedral AgX/Ag 3 PO 4 (X = Cl, Br, I) heterocrystals with enhanced photocatalytic properties and stabilities. Phys. Chem. Chem. Phys. 13, 10071–10075 (2011). Schemes Schemes 1-2 are available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files si202305301.pdf Schemes.docx Cite Share Download PDF Status: Published Journal Publication published 01 Feb, 2024 Read the published version in Nature Communications → 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-3026923","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":210421036,"identity":"9cda6cc8-f83c-4f96-8a5a-7fd6bf651c0c","order_by":0,"name":"Lirong Guo","email":"","orcid":"","institution":"Shandong University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Lirong","middleName":"","lastName":"Guo","suffix":""},{"id":210421037,"identity":"d68a8862-31ba-464a-a150-0dd2ef35b815","order_by":1,"name":"Rongchen Chu","email":"","orcid":"","institution":"Shandong 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03:25:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3026923/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3026923/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-024-45217-y","type":"published","date":"2024-02-01T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":38840488,"identity":"13490d09-9b1c-434b-b121-9daa900ea374","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":39659,"visible":true,"origin":"","legend":"\u003cp\u003ea) Requirements for using anethole radical cation (\u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e•+\u003c/strong\u003e\u003c/sup\u003e) in photocatalytic constructing functionalized molecules from anethole (\u003cstrong\u003e1a\u003c/strong\u003e). b) The band positions of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and commonly applied photocatalysts.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/6d092720b71b0a294ff3cfaf.png"},{"id":38841134,"identity":"094cd467-5a03-46e4-be36-559b02239816","added_by":"auto","created_at":"2023-06-20 21:03:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":104067,"visible":true,"origin":"","legend":"\u003cp\u003ea)\u003cstrong\u003e \u003c/strong\u003eAn SEM image of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. b) The UV-vis diffuse-reflectance spectrum (smooth blue curve) and the AQY action spectrum (red diamond marks; see Supporting Information for calculation method) of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. c)\u003cstrong\u003e \u003c/strong\u003eThe conversion of \u003cstrong\u003e1a\u003c/strong\u003e (green) and yield of \u003cstrong\u003e2a\u003c/strong\u003e (red) during reuse of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. d) The conversion of \u003cstrong\u003e1a\u003c/strong\u003e (green) and yield of \u003cstrong\u003e2a\u003c/strong\u003e (red) by various photocatalysts. The unspecified conditions in panels b-d are: \u003cstrong\u003e1a\u003c/strong\u003e, 0.5 mmol; photocatalyst, 12 mol%; HFIP, 1.5 mL; light source, 425 ± 10 nm LED (120 mW cm\u003csup\u003e-2\u003c/sup\u003e); N\u003csub\u003e2\u003c/sub\u003e atmosphere; 0 °C; 12 h. In panel d, a 395 ± 10 nm LED lamp (119 mW cm\u003csup\u003e-2\u003c/sup\u003e) was used for TiO\u003csub\u003e2\u003c/sub\u003e. The reaction time was optimized for each photocatalyst, reaching up to 24 h for TiO\u003csub\u003e2\u003c/sub\u003e. The yields were determined by \u003csup\u003e1\u003c/sup\u003eH NMR using 4-ethoxybenzaldehyde as the internal standard.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/ae286da00b8695a8497c4110.png"},{"id":38840491,"identity":"e698cac2-088b-4a68-a8fb-26e6cc98f39c","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":337851,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScope of the Ag\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e photocatalysis in the radical cation pericyclic reactions.\u003c/strong\u003e \u003csup\u003ea \u003c/sup\u003eConditions for homo [2+2] reactions: substrate, 1.0 mmol; Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, 12 mol%; 12-18 h. \u003csup\u003eb \u003c/sup\u003eConditions for hetero [2+2] reactions: \u003cstrong\u003e1a\u003c/strong\u003e, 0.5 mmol; the counterpart, 1.0 mmol; Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, 20 mol%; 12 h. \u003csup\u003ec \u003c/sup\u003eConditions for intramolecular [2+2] reactions: substrate, 0.3 mmol; Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, 10 mol%; 12 h.\u0026nbsp; \u003csup\u003ed \u003c/sup\u003eConditions for [4+2] reactions: styrene, 1.0 mmol; diene, 2.0 mmol; Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, 8 mol%; 8 h.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/f991f312f601e1eef4601359.png"},{"id":38841133,"identity":"226e69d2-31df-47f1-9939-8d05900554f5","added_by":"auto","created_at":"2023-06-20 21:03:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":31442,"visible":true,"origin":"","legend":"\u003cp\u003ea)\u003cstrong\u003e \u003c/strong\u003eTransient absorption spectra of \u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e•+\u003c/strong\u003e\u003c/sup\u003e obtained at various times after a 10-ns 355-nm pulse irradiation of the \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP system at room temperature under an air atmosphere. Before LFP, the suspension was ultrasonicated for 30 min to enhance the dispersion of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in HFIP. b)\u003cstrong\u003e \u003c/strong\u003eThe transient absorption spectra obtained without \u003cstrong\u003e1a\u003c/strong\u003e or Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e: black, t = 0; red, 250 μs; blue, 500 μs. c) The decay kinetics of \u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e•+\u003c/strong\u003e\u003c/sup\u003e after 355-nm pulse irradiation. d) The kinetics of \u003cstrong\u003e2a\u003c/strong\u003e formation in the light on-off experiment.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/da57bccd00a031e3a1779424.png"},{"id":38840489,"identity":"2531fefe-c206-4c48-8e33-0deae3fdef1d","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":33757,"visible":true,"origin":"","legend":"\u003cp\u003ea) The adsorption isotherm of \u003cstrong\u003e1a\u003c/strong\u003e and \u003cstrong\u003e2a\u003c/strong\u003e on spherical Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs. \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eb-d) The AQY values of the \u003cstrong\u003e1a\u003c/strong\u003e→\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition reaction as functions of (\u003cem\u003eГ\u003c/em\u003e/\u003cem\u003eГ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e)\u003csup\u003e2\u003c/sup\u003e or \u003cem\u003eГ\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e. The scattered points represent the experimental values, and the red lines are the curve fit or linear fits. Abbreviations for panel c: tetrahydrofuran, THF; ethyl acetate, EA; trifluoroethanol, TFE. The SEM images, facets, and surface energies of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs are indicated in panel d.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/69873eb867c5c3b14bad20a6.png"},{"id":38840494,"identity":"3c821e2e-12e9-4a7d-8cba-c155103e42a4","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":271015,"visible":true,"origin":"","legend":"\u003cp\u003ea-d) The lowest-energy configurations of \u003cstrong\u003e1a\u003c/strong\u003e and \u003cstrong\u003e2a\u003c/strong\u003e molecules on the 2×2 region of the PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3−\u003c/sup\u003e-terminated (100) facet of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. a) and c) are the top views. b) and d) are the side views. The labels \u003cem\u003ea\u003c/em\u003e and \u003cem\u003eb\u003c/em\u003e denote the cell axes. The pale-yellow spheres represent PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3−\u003c/sup\u003e (\u003cem\u003er\u003c/em\u003e = 2.38 Å), and the cyan spheres represent Ag\u003csup\u003e+ \u003c/sup\u003e(\u003cem\u003er\u003c/em\u003e = 0.67 Å). \u003cstrong\u003e1a\u003c/strong\u003e and \u003cstrong\u003e2a\u003c/strong\u003e molecules are drawn to scale. e) The atomic Bader charges of adsorbed \u003cstrong\u003e1a\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/800e8ab1aa472fd2c2e73077.png"},{"id":38840495,"identity":"15fe8c35-d23d-441d-88ad-0fb5911691d5","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":111750,"visible":true,"origin":"","legend":"\u003cp\u003eA plausible mechanism. (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)* denotes a photo-excited Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NP with many \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e and \u003cem\u003eh\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e. The purple-blue spheres are used to show that in (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)* and (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003csup\u003e\u003cem\u003en\u003c/em\u003e\u003c/sup\u003e\u003csup\u003e\u003cstrong\u003e−\u003c/strong\u003e\u003c/sup\u003e NPs, the \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e is shared by silver cations, resulting in a fraction charge of \u003cem\u003eδ\u003c/em\u003e+ (0 \u0026lt; \u003cem\u003eδ\u003c/em\u003e \u0026lt; 1) on each cation.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/eca8ba36032e2f2200c36913.png"},{"id":50543289,"identity":"fd27f5ea-f8dc-46f1-8c0e-64b34362c277","added_by":"auto","created_at":"2024-02-02 08:23:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1379151,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/f0ee987e-c3ea-4114-b8fb-5934d6b500e1.pdf"},{"id":38840496,"identity":"3e6e9e26-2aa4-4328-89a5-b5d6f420e87d","added_by":"auto","created_at":"2023-06-20 20:55:38","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":11559969,"visible":true,"origin":"","legend":"","description":"","filename":"si202305301.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/3c5e5c658191c689e6d610a4.pdf"},{"id":38840492,"identity":"096d07f8-5a44-4ed5-9fed-22180964ac67","added_by":"auto","created_at":"2023-06-20 20:55:37","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1736427,"visible":true,"origin":"","legend":"","description":"","filename":"Schemes.docx","url":"https://assets-eu.researchsquare.com/files/rs-3026923/v1/236d3ca844bd62c1ebfee8d5.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions","fulltext":[{"header":"Introduction","content":"\u003cp\u003eStyrene radical cations, which are one electron (1e)-oxidation intermediates of styrenes, play important roles in the synthesis of complex functionalized molecules and cyclic moieties, particularly the [2+2] and [4+2] pericyclic products. To generate and make use of styrene radical cations, extensive efforts have been devoted for a long time. Compared to single electron oxidants\u0026nbsp;such as Ce\u003csup\u003e4+\u003c/sup\u003e,\u003csup\u003e1\u003c/sup\u003e Fe\u003csup\u003e3+\u003c/sup\u003e,\u003csup\u003e2\u003c/sup\u003e and hypervalent iodine reagents,\u003csup\u003e3, 4\u003c/sup\u003e photocatalysts (PCs) generate highly oxidizing holes under sunlight irradiation and operate under mild conditions, making photocatalysis a green and sustainable strategy for radical cation-mediated reactions.\u003csup\u003e5-15\u003c/sup\u003e However, the PCs utilised for generating radical cations are primarily homogeneous organic compounds, particularly transition metal-coordination complexes\u003csup\u003e8-11\u003c/sup\u003e and \u0026pi;-conjugated molecules.\u003csup\u003e12-15\u003c/sup\u003e Meanwhile, the scope of the approaches is constrained by the short lifetime of radical cations (on a \u0026mu;s scale\u003csup\u003e16-22\u003c/sup\u003e). In contrast, inorganic semiconductor PCs (isPCs), such as TiO\u003csub\u003e2\u003c/sub\u003e, CdS, Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, have been widely employed for solar light harvesting applications including water splitting, organic pollutant degradation, and photoelectric conversion.\u003csup\u003e23\u003c/sup\u003e From a practical standpoint, they are generally considered stable,\u0026nbsp;recyclable, inexpensive, and environmentally friendly, making them an ideal choice for use in photosynthesis. However, the efficiency of isPCs in the 1e-oxidative activation of non-polar and non-coordinative C=C moieties on their surfaces is typically low.\u003csup\u003e16, 19, 20, 24-31\u003c/sup\u003e One obstacle is the extremely short lifetime of holes (fs to ns\u003csup\u003e32\u003c/sup\u003e), which significantly slows down the 1e-oxidation of the C=C moieties (Figure 1a). Moreover, even if some alkene radical cations are slowly generated at the surfaces of a traditional isPC like TiO\u003csub\u003e2\u003c/sub\u003e, they undergo\u0026nbsp;few\u0026nbsp;intermolecular C-C formation reactions.\u003csup\u003e16\u003c/sup\u003e Instead, they are more prone to nucleophilic attack by long-lived photogenerated electrons (\u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e), resulting in ineffective 1e-oxidation. These hindrances lead to a diminished quantum yield of light (i.e. reduced reaction rate) and low product yield, regardless of reaction time. Therefore, it is imperative to extend the lifespan of alkene radical cations for affordable and recyclable PCs that can effectively harvest sunlight for pericyclic reactions. However, this remains an ongoing challenge.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAmong all the available isPCs, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e stands out as one of the few that exhibits an inherent visible-light response.\u003csup\u003e33\u003c/sup\u003e It has been extensively used in visible-light-driven water oxidation\u003csup\u003e33-35\u003c/sup\u003e and organic pollutant degradation.\u003csup\u003e35, 36\u003c/sup\u003e Compared to other commonly used semiconductors, it produces strong oxidizing holes and weak reducing electrons under visible-light irradiation (+2.9 V and +0.45 V \u003cem\u003evs.\u003c/em\u003e NHE; Figure 1b). Moreover, the surfaces of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e are rich in large PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e anions with high-charge-density that can strongly electrostatically interact with cationic species such as radical cations. As a result, photo-excited Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs may efficiently generate but inefficiently quench radical cations, allowing for the accumulation of radical cations to facilitate radical cation-mediated reactions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this study, we demonstrate that Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e efficiently catalyse intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible light or solar irradiation. The system exhibit remarkable efficiency with respect to substrate scope, product yield, diastereoselectivity, apparent quantum yield (AQY), and scaleup synthesis under solar irradiation. Two critical aspects of the reaction mechanism are validated: (1) the existence of long-lived \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e radical cation on the surfaces of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs that are photo-reduced\u0026nbsp;in situ, (2) the acceleration of rate-limiting step by prolonging the lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e. To the best of our knowledge, this is the first report on employing an isPC for pericyclic reaction under visible-light irradiation. Our discoveries may pave the way for employing highly active organic radical cations and even radical anions in critical pericyclic processes.\u0026nbsp;\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eTransformation of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003estyrene\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;1a to\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003etrans\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e-cyclobutane 2a\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnethole\u0026nbsp;(\u003cstrong\u003e1a\u003c/strong\u003e) has been the most studied electron-rich \u003cem\u003e\u0026beta;\u003c/em\u003e-substituted styrene in [2+2] cycloaddition reactions.\u003csup\u003e3, 18, 37\u003c/sup\u003e Therefore, it was selected as the model compound to evaluate the photocatalytic perfomance of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (Scheme 1). Although different Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e samples exhibited in distinct reaction rates, they hardly affected final product yields. Thus, a self-synthesized Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e sample coomposed of nanospheres with a diameter of 230 \u0026plusmn; 60 nm was used for further studies (Figure 2a). The cycloaddition reaction was conducted under an N\u003csub\u003e2\u003c/sub\u003e atmosphere by irradiating a suspension of reactant \u003cstrong\u003e1a\u003c/strong\u003e in hexafluoroisopropanol (HFIP) solvent containing a catalytic quantity of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (12 mol%) at 0 \u0026deg;C. No additive was introduced. The conversion of \u003cstrong\u003e1a\u003c/strong\u003e proceeded smoothly, affording \u003cem\u003etrans\u003c/em\u003e-cyclobutane \u003cstrong\u003e2a\u003c/strong\u003e as the sole product (see Figure S1 for the time-resolved \u003csup\u003e1\u003c/sup\u003eH NMR spectra and kinetics). After 12 h of reaction, the yield of \u003cstrong\u003e2a\u003c/strong\u003e reached 82%, indicating a highly diastereoselective process (\u003cem\u003ed.r.\u003c/em\u003e \u0026gt;19:1). Further irradiation did not affect conversion due to equilibration between \u003cstrong\u003e1a\u003c/strong\u003e and \u003cstrong\u003e2a\u003c/strong\u003e (Figure S2), as commonly observed in photocatalyzed radical cation processes.\u003csup\u003e37, 38\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe control experiments demonstrate that in the absence of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e or light at room temperature, or stirring the reaction mixture in the dark at 80 \u0026deg;C, no conversion of \u003cstrong\u003e1a\u003c/strong\u003e occurs (see Table S1 for screening of the experimental conditions). Therefore, both light and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e are indispensable for the reaction, excluding the possibility of a thermocatalytic mechanism. The AQY values were determined according to the initial 30-min yield. As shown in Figure 2b, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e can effectively harvest visible light up to 500 nm to initiate the \u003cstrong\u003e1a\u0026rarr;2a\u003c/strong\u003e cycloaddition, which is close to its\u003csub\u003e\u0026nbsp;\u003c/sub\u003eabsorption edge. The action spectrum of AQY matches the UV-vis diffuse-reflectance spectrum of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. Although we were aware that depositing AgNPs on the surfaces of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e could enhance its photo-absorption and charge-separation efficiency,\u003csup\u003e39\u003c/sup\u003e our experiments with the AgNPs-loaded sample, i.e., Ag/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, affording a substantially lower yield (optimum yield = 60% after 24 h). This suggests that AgNPs are not the photocatalyst. Therefore, it can be concluded that Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is the true photocatalyst.\u003c/p\u003e\n\u003cp\u003eSilver salt-based photocatalysts often suffer from photo-corrosion.\u003csup\u003e40-43\u003c/sup\u003e However, in the current system, the 12 mol% of initially added Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e successfully worked five consecutive photocatalytic cycles with only a slight decrease in efficiency (Figure 2c), resulting in a turnover number of 13. Photo-corrosion of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e was observed as evidenced by its significant darkening after five cycles. The TEM image indicates the formation of\u0026nbsp;numerous AgNPs\u0026nbsp;on the surfaces of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (Figure S3). Nevertheless,\u0026nbsp;regeneration of\u0026nbsp;the recycled sample was achieved through a simple immersion in 6.7 mM Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e aqueous solution and addition a drop of 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e44\u003c/sup\u003e Within minutes,\u0026nbsp;color, microscopic morphology, and photocatalytic performance were fully restored (Figure S3). As shown in Figure 2d, while other silver salts such as AgCl, AgBr, and AgI, exhibit activity, their \u003cstrong\u003e1a\u003c/strong\u003e conversion and \u003cstrong\u003e2a\u003c/strong\u003e selectivity are significantly lower than that of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. Furthermore, both AgCl and AgBr suffer from\u0026nbsp;severe\u0026nbsp;photo-corrosion. In comparison to the widely studied heterogeneous photocatalysts\u003csup\u003e45\u003c/sup\u003e including graphitic carbon nitride (g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e), Bi\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e6\u003c/sub\u003e, and TiO\u003csub\u003e2\u003c/sub\u003e, the performance of\u0026nbsp;Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is superior.\u0026nbsp;For example, the reaction rate was notably low over TiO\u003csub\u003e2\u003c/sub\u003e even under UV. Furthermore, electron accumulation caused\u0026nbsp;TiO\u003csub\u003e2\u003c/sub\u003e to exhibit blue hue\u0026nbsp;and ultimately became completely inert once conversion reached 18% (Figure S4). Table S2 shows that Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e performs\u0026nbsp;comparably to state-of-art PCs and single-electron oxidants such as Ru(bpm)\u003csub\u003e3\u003c/sub\u003e(BArF)\u003csub\u003e2\u003c/sub\u003e,\u003csup\u003e37\u003c/sup\u003e PhI(OAc)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e3\u003c/sup\u003e and Fe(ClO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e in the \u003cstrong\u003e1a\u0026rarr;2a\u003c/strong\u003e cycloaddition.\u003csup\u003e18\u003c/sup\u003e Therefore, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is highly applicable for [2+2] cyclobutanation reactions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAg\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/visible light system for pericyclic reactions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGiven the success of the [2+2] homo-cycloaddition of \u003cstrong\u003e1a\u003c/strong\u003e, we sought to explore whether the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/visible light system could serve as a versatile tool for achieving various pericyclic reactions. Our initial focus was on investigating the scope of the intermolecular dimerization reaction. As shown in Figure 3, a diverse range of electron-rich styrenes with varying substituents underwent smooth\u0026nbsp;reaction,\u0026nbsp;affording the corresponding symmetrical cyclobutanes in moderate to good yields and excellent diastereoselectivity (\u003cstrong\u003e2a\u003c/strong\u003e-\u003cstrong\u003e2h\u003c/strong\u003e, yield ranges 42%-83%,\u003cem\u003e\u0026nbsp;d.r.\u003c/em\u003e \u0026gt; 19:1). Electronic density of the aromatic ring and steric hindrance at \u003cem\u003e\u0026beta;\u003c/em\u003e-site exert a noticeable influence on the reaction outcome (\u003cstrong\u003e2b\u003c/strong\u003e \u003cem\u003evs.\u003c/em\u003e \u003cstrong\u003e2c\u003c/strong\u003e, \u003cstrong\u003e2a\u003c/strong\u003e \u003cem\u003evs.\u003c/em\u003e \u003cstrong\u003e2d-2f\u003c/strong\u003e). However, this catalytic system exhibits high tolerance toward steric hindrance at the benzene ring (\u003cstrong\u003e2a\u003c/strong\u003e \u003cem\u003evs.\u003c/em\u003e \u003cstrong\u003e2f\u003c/strong\u003e-\u003cstrong\u003e2h\u003c/strong\u003e). Notably, NO\u003csub\u003e2\u003c/sub\u003e-, OH-, and COOH-substituted styrenes were challenging substrates for other [2+2] cycloaddition catalytic systems,\u003csup\u003e46\u003c/sup\u003e as well as the current Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e system (Table S3). Finally, we achieved a 70% isolated yield of magnosalin (\u003cstrong\u003e2h\u003c/strong\u003e), a valuable natural product. We then use the system to synthesize unsymmetric cyclobutanes and were pleased to discover that a variety of styrenes, including unsubstituted styrene (\u003cstrong\u003e4a\u003c/strong\u003e) and substituted styrenes with electron-donating groups (EDGs; \u003cstrong\u003e4b\u003c/strong\u003e, \u003cstrong\u003e4d, 4i\u003c/strong\u003e) and electron-withdrawing groups (EWGs;\u003cstrong\u003e\u0026nbsp;4c, 4e, 4f, 4g, 4h\u003c/strong\u003e) at both ortho-, meta- and para-sites of the benzene rings, could be employed as model reaction counterparts using \u003cstrong\u003e1a\u003c/strong\u003e. The sole byproduct resulting from these crossed reactions is the homo-cycloaddition product, e.g., \u003cstrong\u003e2a\u003c/strong\u003e. However, because the crossed reactions are much faster than the homo-cycloaddition (see Figure S5 for a comparison of the rates), introducing \u003cstrong\u003e1a\u003c/strong\u003e via a syringe pump would inhibit the homo [2+2] reaction. Next, we explored the feasibility of intramolecular [2+2] cycloaddition, an efficient approach for synthesizing fused heterocycles.\u003csup\u003e6\u003c/sup\u003e Strikingly, all tested bis(styrene)s afforded good to excellent yields of the desired cyclobutanes (\u003cstrong\u003e6a\u003c/strong\u003e-\u003cstrong\u003e6t\u003c/strong\u003e). The intramolecular [2+2] cycloadditions exhibit a broad tolerance toward EDGs, EWGs, and the steric hindrance at both the benzene ring and the \u003cem\u003e\u0026beta;\u003c/em\u003e-site. The\u0026nbsp;Diels-Alder reaction is considered one of the essential C-C bond-forming reactions in the synthetic organic chemistry. Recent studies have shown that photocatalytic methods are effective in the radical-cation-mediated cycloadditions of electron-rich olefins and dienes,\u003csup\u003e47-49\u003c/sup\u003e which are challenging substrates for conventional thermal processes. In this study, we found that even with a reduced Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e loading of 8 mol%, the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/visible light system was still capable of facilitating Diels-Alder cycloadditions\u0026nbsp;-involving\u0026nbsp;the radical cations. Moreover, the 8 mol% of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e was successfully reused for five consecutive runs without any noticeable decrease in performance (Figure S6). Based on the substituted styrenes, the yields achieved in all tested reactions are near unity (\u003cstrong\u003e8a\u003c/strong\u003e-\u003cstrong\u003e8h\u003c/strong\u003e).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe remarkable diastereoselectivity of\u0026nbsp;the reactions is noteworthy. Specifically, nearly all intermolecular [2+2] products are \u003cem\u003etrans\u003c/em\u003e; intramolecular [2+2] products are predominately \u003cem\u003ecis\u003c/em\u003e, and nearly all Diels-Alder reactions yield \u003cem\u003etrans\u003c/em\u003e products.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eScale synthesis of [2+2] and [4+2] reactions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo investigate the synthetic potential of the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/visible light system, we performed large-scale [2+2] and [4+2] reactions under natural sunlight irradiation by placing the reaction flasks on a windowsill at ambient temperatures (1-10 \u0026deg;C). The sunlight intensity ranged from 15-23 mW cm\u003csup\u003e-2\u003c/sup\u003e. Interestingly, 41.5 g of the [4+2] cycloaddition product \u003cstrong\u003e8a\u003c/strong\u003e was obtained almost quantitatively in a one-pot reaction after only six hours of irradiation (Scheme 2). After being filtered through diatomite, the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solid was removed, resulting in nearly pure \u003cstrong\u003e8a\u003c/strong\u003e (41.5 g), which confirms the method\u0026rsquo;s flexibility and ease of use. The intermolecular [2+2] homo-cycloaddition of \u003cstrong\u003e1a\u003c/strong\u003e yielded a 60% yield of \u003cstrong\u003e2a\u003c/strong\u003e (100% selectivity) before Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (5 mol%) became deactivated. However, upon reintroduction of regenerated Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e into the catalytic system, a final yield of 80% of \u003cstrong\u003e2a\u003c/strong\u003e was achieved (Scheme 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTables S4-S6 demonstrate the superior performance of the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/visible light system compared to the state-of-art reports in [2+2] and Diels-Alder cycloadditions. The current system boasts one of the highest efficiencies heterogeneous systems, with broad light absorption. It is the only one capable of realizing intramolecular and intermolecular 2+2 cycloadditions and Diels-Alder reactions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanism study and DFT simulations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLaser flash photolysis (LFP) was performed to detect the transient species involved in the photocatalytic \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition. The transmittance LFP spectra of a \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP suspension are depicted in Figure 4a. The two distinct, intense peaks centered at ca. 387 and 605 nm precisely match the spectra of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e generated by photolysis of homogeneous solutions of \u003cstrong\u003e1a\u003c/strong\u003e/H\u003csub\u003e2\u003c/sub\u003eO-MeCN at 266 nm\u003csup\u003e50\u003c/sup\u003e and \u003cstrong\u003e1a\u003c/strong\u003e/MeCN at 308 nm,\u003csup\u003e51\u003c/sup\u003e respectively, as reported in previous studies. Figure 4b demonstrates that the absence of \u003cstrong\u003e1a\u003c/strong\u003e or Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e resulted in no signal from a 355-nm laser pulse, indicating the indispensability of both \u003cstrong\u003e1a\u003c/strong\u003e and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e for the formation of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e. Hence, the LFP spectra confirm that photogenerated\u003cem\u003e\u0026nbsp;h\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e faciliates the 1e-oxidation of \u003cstrong\u003e1a\u003c/strong\u003e to afford \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe concentration of a transient species, which is determined by both formation rate and lifetime, is essential for detecting it via LFP. Hence, the observation of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e in the \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP system suggests that \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e forms rapidly and has a long life, allowing for its accumulation due to its formation far exceeding decay. Recall Figure 4a, the sample initially exhibited strong background absorption, which significantly decreased\u0026nbsp;after\u0026nbsp;250 \u0026mu;s due to the sedimentation of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs. The spectra at 250 and 500 \u0026mu;s showed similar level of background absorption, indicating that sedimentation was minor during this time period. Based on this understanding,\u0026nbsp;we measured\u0026nbsp;the decay kinetics of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e in\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ethe \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP suspension at \u0026lambda; = 600 nm. Figure 4c demonstrates that the signal intensity decayed significantly before 500 \u0026mu;s, which could be mostly attributable to the sedimentation mentioned above of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs. Afterward, the signal intensity remained nearly constant until 1900 \u0026mu;s, suggesting that the lifetime of \u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u0026bull;+\u003c/sup\u003e in the \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP system must be more than 1900 \u0026mu;s.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe conducted light-on-off experiments to investigate the lifetime of\u0026nbsp;\u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e in the \u003cstrong\u003e1a\u003c/strong\u003e/Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e/HFIP system. The reaction vial was either left\u0026nbsp;stirring\u0026nbsp;in the dark after turning off the light or centrifuged to settle down the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs before being left in the dark. In the former situation, over the next six hours, there was a gradual increase of ca. 8% in yield of \u003cstrong\u003e2a\u003c/strong\u003e (Figure 4d), indicating that \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e could maintain its reactivity for many hours. This is distinct from the homogeneous systems, where the \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition practically ceased upon light-off.\u003csup\u003e52\u003c/sup\u003e In the dark reaction without agitation, the yield of \u003cstrong\u003e2a\u003c/strong\u003e remained unchanged after Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e settled down (Figure 4d). It indicates that the long-lived \u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u0026bull;+\u003c/sup\u003e radical cations must remain adsorbed on the surfaces of the reduced Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs (denoted as (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003cem\u003e\u003csup\u003en\u003c/sup\u003e\u003c/em\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e, where \u003cem\u003en\u003c/em\u003e is the number of \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e per NP). When all the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs settled down, the \u003cstrong\u003e1a\u003c/strong\u003e molecules in solution could not reach \u003cstrong\u003e1a\u003c/strong\u003e\u003csup\u003e\u0026bull;+\u003c/sup\u003e, and thus the cycloaddition ceased. This further confirms that the radical cation-mediated [2+2] pericyclic reaction occurs on the surfaces of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e rather than in the solution.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIt was reported that the decay rate constant\u003csup\u003e50, 53\u003c/sup\u003e of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e is 4 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e in aerated MeCN, corresponding to a very short lifetime of 25 \u0026mu;s.\u003csup\u003e51\u003c/sup\u003e This is likely why the \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition stopped nearly instantly upon light-off in homogeneous systems.\u003csup\u003e21, 52\u003c/sup\u003e To probe the lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u0026nbsp;\u003c/strong\u003ein neat HFIP, we used a 266-nm laser pulse to excite a\u0026nbsp;\u003cstrong\u003e1a\u003c/strong\u003e/HFIP solution. However, the system produced signals from unknown species and the absorption peaks of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e at\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eca. 387 and 605 nm were not detected. This may suggest that the lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e in HFIP is too short, resulting in a \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e concentration below the detection limit. We also used a 355-nm laser pulse to excite the \u003cstrong\u003e1a\u003c/strong\u003e/TiO\u003csub\u003e2\u003c/sub\u003e/HFIP system, which produced an 16% yield of \u003cstrong\u003e2a\u003c/strong\u003e, indicating that photo-excited TiO\u003csub\u003e2\u003c/sub\u003e NPs generated \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e. However, the transient spectrum of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e was not detected by LFP (Figure S7), implying that its lifetime in the system is also very short.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe found that the adsorption of reactant \u003cstrong\u003e1a\u003c/strong\u003e and desorption of product \u003cstrong\u003e2a\u003c/strong\u003e are crucial in the reaction. Figure 5a shows that the adsorption of \u003cstrong\u003e1a\u003c/strong\u003e on the (100)-facet-rich spherical Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs (as the representative example) can fit well to the Langmuir type-I isotherm (eq 1),\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eГ\u003c/em\u003e is the adsorbed amount at the adsorption/desorption equilibrium concentration \u003cem\u003eC\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e. The Langmuir coefficient \u003cem\u003eK\u003c/em\u003e and the capacity of adsorption \u003cem\u003eГ\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e are calculated to be 5.8 \u0026plusmn; 0.6 M\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 2.9 \u0026plusmn; 0.1 mmol g\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. In contrast, the adsorption of \u003cstrong\u003e2a\u003c/strong\u003e on Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces is barely detectable, indicating very weak adsorption of \u003cstrong\u003e2a\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAt low \u003cstrong\u003e1a\u003c/strong\u003e concentrations, the AQY values increase dramatically with the initially added concentration of \u003cstrong\u003e1a\u003c/strong\u003e but then approach a plateau (Figure S8). This differs from a typical homogeneous bimolecular reaction, which is second order depending on the substrate concentration. Instead, the AQY values are well linearly correlated with the square of the fractional coverage of \u003cstrong\u003e1a\u003c/strong\u003e, \u003cem\u003eƟ\u0026nbsp;\u003c/em\u003e(eq 2),\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003ek\u003c/em\u003e denotes the slope of the plot (Figure 5b). This kinetic equation corroborates that the conversion of\u0026nbsp;\u003cstrong\u003e1a\u003c/strong\u003e through photocatalysis occurs on the\u0026nbsp;Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surface. The rate-limiting step (RLS) of the\u0026nbsp;formation of\u0026nbsp;\u003cstrong\u003e2a\u003c/strong\u003e involves two molecular species of\u0026nbsp;\u003cstrong\u003e1a\u003c/strong\u003e adsorbed on the surface. We also observe a significant solvent effect in the performance of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in the \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition reaction (Figure 5c). Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e did not perform well in EtOAc, \u003cem\u003en\u003c/em\u003e-hexane or CH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e, but performed better in CH\u003csub\u003e3\u003c/sub\u003eCN, MeNO\u003csub\u003e2\u003c/sub\u003e and TFE, and performed best in HFIP. Surprisingly, eq 2 applies to the results from different solvents. Thus, solvents influence the AQY by modulating the\u0026nbsp;\u003cstrong\u003e1a\u0026nbsp;\u003c/strong\u003edistribution between the bulk solution and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces. It has been reported that the facets\u0026nbsp;of photocatalysts\u0026nbsp;substantially influence their activities, especially in the case of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e.\u003csup\u003e34, 35, 54, 55\u003c/sup\u003e For the \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition reaction,\u0026nbsp;we used\u0026nbsp;the spherical, rhombic dodecahedral, cubic, and tetrahedral NPs of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e,\u0026nbsp;which are rich in {100}, {110}, {100} and {111} facets, respectively,\u003csup\u003e34\u003c/sup\u003e.\u0026nbsp;Figure 5d displays distinct AQYs on different facets and eq 2 is applicable\u0026nbsp;to the results from various Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e facets.\u0026nbsp;Overall, Figure 5 indicates that the photocatalytic cycloaddition reaction on\u0026nbsp;Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces\u0026nbsp;follows the Langmuir-Hinshelwood mechanism for a bimolecular reaction. It also implies that the interaction between \u003cstrong\u003e1a\u003c/strong\u003e and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces is vital in the success of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in the photocatalytic [2+2] cycloadditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe conducted DFT simulations to determine the mechanism of interfacial interactions between \u003cstrong\u003e1a\u003c/strong\u003e (and \u003cstrong\u003e2a\u003c/strong\u003e)\u0026nbsp;and the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces. As the (100) facet is the lowest-energy facet of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e crystals\u003csup\u003e34, 35, 55\u003c/sup\u003e and the primary surface of spherical Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs, we selected the PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e-terminated and the Ag\u003csup\u003e+\u003c/sup\u003e-terminated (100) facets to calculate the optimal adsorption configurations (see Figures S9-S10 for details of results). Figure 6 displays the lowest-energy configurations of \u003cstrong\u003e1a\u003c/strong\u003e and \u003cstrong\u003e2a\u0026nbsp;\u003c/strong\u003emolecules on the PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e-terminated (100) facet. It should be noted that the size of\u0026nbsp;PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e is much larger than that of Ag\u003csup\u003e+\u003c/sup\u003e (2.38 \u0026Aring; vs. 0.67 \u0026Aring;), but comparable to molecule \u003cstrong\u003e1a\u003c/strong\u003e in size. Molecule \u003cstrong\u003e1a\u003c/strong\u003e lies parallel to the facet, with its long axis aligned with the \u003cem\u003ea\u003c/em\u003e-axis of the crystal lattice, and the CH=CH moiety positioned close to the O\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions of PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. In this configuration, each \u003cstrong\u003e1a\u003c/strong\u003e molecule intimately contacts four PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e anions, maximizing the interfacial interaction between \u003cstrong\u003e1a\u003c/strong\u003e and the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surface. The strong interaction is consistent with the previously discussed adsorption of \u003cstrong\u003e1a\u003c/strong\u003e to the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces. This adsorption mode should be beneficial for the 1e-oxidation of the CH=CH moiety upon photo-excitation of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e since photogenerated holes are localized at O of PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e.\u003csup\u003e56\u003c/sup\u003e The energy required for adsorption of each \u003cstrong\u003e1a\u003c/strong\u003e molecule from the vacuum is \u0026minus;2.10 eV (Figure 6, ab). In contrast, the calculated energies for \u003cstrong\u003e1a\u003c/strong\u003e adsorption onto PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e-terminated (100) facet along the \u003cem\u003eb\u003c/em\u003e-axis and that\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eonto the Ag\u003csup\u003e+\u003c/sup\u003e-terminated (100) facet along both the \u003cem\u003ea\u003c/em\u003e- and \u003cem\u003eb\u003c/em\u003e-axis, are\u0026nbsp;substantially smaller at\u0026nbsp;\u0026minus;1.67, \u0026minus;1.54, and \u0026minus;1.54 eV, respectively\u0026nbsp;(Figures S9-S10). These lower adsorption energies can be attributed to the greater spacing between the adjacent\u0026nbsp;PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e anions on these facets, which weakens the contact between \u003cstrong\u003e1a\u003c/strong\u003e and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. However, due to the large steric effects of the \u003cstrong\u003e2a\u003c/strong\u003e molecule, each \u003cstrong\u003e2a\u003c/strong\u003e has an optimum adsorption energy of \u0026minus;1.56 eV when adsorbed on the PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e-terminated (100) facet (Figure 6, cd). The above calculations reveal a large adsorption energy difference between two \u003cstrong\u003e1a\u003c/strong\u003e and one \u003cstrong\u003e2a\u003c/strong\u003e, i.e., +2.64 eV on the PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e-terminated Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (100) facet in a vacuum. The much weaker adsorption of \u003cstrong\u003e2a\u003c/strong\u003e suggests that the \u003cstrong\u003e1a\u003c/strong\u003e\u0026rarr;\u003cstrong\u003e2a\u003c/strong\u003e cycloaddition on the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces benefits from the easier removal of product \u003cstrong\u003e2a\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe atomic Bader charges shown in Figure 6e indicate that the electron density of \u003cstrong\u003e1a\u003c/strong\u003e changes upon adsorption. The overall Bader charge of adsorbed \u003cstrong\u003e1a\u003c/strong\u003e is 0.34e, indicating a transfer of 0.34e from \u003cstrong\u003e1a\u003c/strong\u003e to the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces during adsorption. The two H-atoms in the CH=CH moiety have enormous Bader charges, namely, 0.1323e and 0.1e, respectively. This, combined with the very negative Bader charge of the CH\u003csub\u003e3\u003c/sub\u003eO moiety (\u0026minus;0.4587e), strongly suggests that polarization occurs in molecule \u003cstrong\u003e1a\u003c/strong\u003e and that its CH=CH group is activated upon adsorption. The high Bader charge also means that the CH=CH group is the most readily oxidized site in \u003cstrong\u003e1a\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 7 illustrates a plausible mechanism for Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e triggering the [2+2] cycloaddition of \u003cstrong\u003e1a\u003c/strong\u003e under visible-light irradiation. Initially, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e adsorbs \u003cstrong\u003e1a\u003c/strong\u003e molecules on its surface via PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e anions (step I). Then, upon excitation, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e generates many \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in the conduction band and \u003cem\u003eh\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e in the valance band (step II). Due to the fact that the conduction band bottom is mainly composed of hybridized Ag 5s5p orbitals,\u003csup\u003e33\u003c/sup\u003e the reduction power of the electrons in the conduction band of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is low (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e = +0.45 V vs. NHE\u003csup\u003e33, 39, 57, 58\u003c/sup\u003e). The unreactive \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e remains in the form of (Ag\u003csup\u003e\u0026delta;+\u003c/sup\u003e)\u003csub\u003em\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, which means it is shared by many Ag\u003csup\u003e+\u003c/sup\u003e ions. The observed AgNP formation substantiates that \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e transfers to Ag\u003csup\u003e+\u003c/sup\u003e ions. The valance band top of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e mainly comprises hybridized O 2p and Ag 4d orbitals. The \u003cem\u003eh\u003c/em\u003e\u003csup\u003e+\u003c/sup\u003e in the valence band has strong oxidation power (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eVB\u003c/sub\u003e = +2.90 V vs. NHE\u003csup\u003e33, 39, 57, 58\u003c/sup\u003e) and able to gain an electron from the CH=CH group of \u003cstrong\u003e1a\u003c/strong\u003e to yield \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003e(step III). The 1e-oxidation of \u003cstrong\u003e1a\u003c/strong\u003e results in the photocatalytically reduced NP with numerous \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e. The \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e species strongly adsorbs on the surfaces of (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003cem\u003e\u003csup\u003en\u003c/sup\u003e\u003c/em\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e. In this case, the electrostatic interaction between \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e and (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003cem\u003e\u003csup\u003en\u003c/sup\u003e\u003c/em\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e NP surfaces is analogous to the interactions in homogeneous solutions described by Yoon et al for \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e with a tetraarylborate anion,\u003csup\u003e17\u003c/sup\u003e Ishihara et al for \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e with FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e,\u003csup\u003e18-20\u003c/sup\u003e and List et al for \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e with an imidodiphosphorimidate counteranion.\u003csup\u003e21\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe adsorbed \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e is stabilized by electrostatic interaction with the\u0026nbsp;(Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003cem\u003e\u003csup\u003en\u003c/sup\u003e\u003c/em\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e surfaces. The\u0026nbsp;low possibility\u0026nbsp;recombination between \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e and\u0026nbsp;\u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e shared by multiple Ag\u003csup\u003e+\u003c/sup\u003e cations, (Ag\u003csup\u003e\u0026delta;+\u003c/sup\u003e)\u003csub\u003em\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, is evidenced by the\u0026nbsp;observation of\u0026nbsp;AgNP formation. As a result, the lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e is dramatically prolonged to hours, which is over 10\u003csup\u003e8\u003c/sup\u003e times longer than in a homogeneous solution (\u0026mu;s level\u003csup\u003e51\u003c/sup\u003e).\u0026nbsp;The long lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e benefits\u0026nbsp;the nucleophilic attack by another adsorbed \u003cstrong\u003e1a\u003c/strong\u003e molecule, allowing the\u0026nbsp;reaction of \u003cstrong\u003e1a\u003c/strong\u003e + \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e \u0026rarr; 2a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e in step IV to proceed (the RLS; see Supporting Information for analysis).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe ability to generate the long-lived radical cation \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e distinguishes (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003cem\u003e\u003csup\u003en\u003c/sup\u003e\u003c/em\u003e\u003cstrong\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/strong\u003e from a traditional photocatalytically reduced TiO\u003csub\u003e2\u003c/sub\u003e NP. On the illuminated\u0026nbsp;TiO\u003csub\u003e2\u003c/sub\u003e NP, the lifetime of \u003cstrong\u003e1a\u003csup\u003e\u0026bull;+\u003c/sup\u003e\u003c/strong\u003e was too short to detect, and the conversion was only 18% (Figure 2d). Okada et al used a substantial excess of TiO\u003csub\u003e2\u003c/sub\u003e (e.g., \u0026gt; 6 eq) to minimize the accumulated electron per NP and extra LiClO\u003csub\u003e4\u003c/sub\u003e (1.0 M) to stabilize the radical cations.\u003csup\u003e18\u003c/sup\u003e\u003csup\u003e,\u0026nbsp;\u003c/sup\u003e\u003csup\u003e22-23\u003c/sup\u003e\u003csup\u003e,\u0026nbsp;\u003c/sup\u003e\u003csup\u003e25-27\u003c/sup\u003e In contrast, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003ephotocatalysis can harvest the visible spectrum of sunlight and achieve a high yield of the desired product without any additives.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAg\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e is a powerful photocatalyst for homo, crossed, intramolecular [2\u0026thinsp;+\u0026thinsp;2], and Diels-Alder [4\u0026thinsp;+\u0026thinsp;2] pericyclic reactions under visible-light irradiation. The catalytic process is mild, straightforward, affordable, additive-free, scalable under sunlight irradiation, and allows for easy product separation and catalyst reuse. It has a broad substrate scope and produces a wide range of desired products in modest to excellent yields. Our study reveals the potential of this photocatalytic process for fine chemical production. We have demonstrated that the rate-limiting step is the reaction between the reactant and its 1e-oxidation intermediate, a radical cation. The lifetime of anethole radical cation (\u003cb\u003e1a\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026bull;+\u003c/b\u003e\u003c/sup\u003e) on the Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e surfaces reaches several hours, which is over 10\u003csup\u003e8\u003c/sup\u003e times longer than that in the homogeneous solutions, thus effectively promotes the rate-limiting step. The long lifetime of \u003cb\u003e1a\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026bull;+\u003c/b\u003e\u003c/sup\u003e is attributed to the appropriate band structure of Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and the strong electrostatic interaction between \u003cb\u003e1a\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026bull;+\u003c/b\u003e\u003c/sup\u003e and the (Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e)\u003csup\u003e\u003cem\u003en\u003c/em\u003e\u003cb\u003e\u0026minus;\u003c/b\u003e\u003c/sup\u003e NP surfaces, which should be a general and essential mechanism for promoting chemical processes mediated by radical cations on heterogeneous surfaces. This may inspire new ideas for more challenging radical cation/anion-mediated solar synthesis using inorganic semiconductor photocatalysts.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eGeneral procedure for the photocatalytic reactions.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe reactions were carried out in 10-mL Pyrex vials. Olefin and Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e were dispersed in a solvent in the vial, which was then purged for 10 min with high-purity N\u003csub\u003e2\u003c/sub\u003e (99.999%). The vial was immersed in a cryogenic reaction bath to maintain the reaction temperature. The reaction suspension was stirred in the dark for 30 min to achieve adsorption-desorption equilibrium. The mixture was then exposed to the lamp from the side. To monitor the reaction progress, a syringe was used to withdraw 10 \u0026micro;L of the solution for analysis by thin-layer chromatography (TLC). After the reaction, the suspension was centrifuged to separate the solid catalyst from the solution. The residue purified with column chromatography to afford the desired pure products.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDetails for the homo-dimerization of styrenes.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo a solution of styrene \u003cb\u003e1\u003c/b\u003e (1.0 mmol) in 3.0 mL of HFIP, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (12 mol%) was added in one portion. The remaining steps are the same as the general procedure.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDetails for the cross-dimerization of styrenes.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo a solution of styrene \u003cb\u003e3\u003c/b\u003e (1.0 mmol, 2.0 eq) in 2.0 mL of HFIP was added Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (20 mol%). Then, the reaction mixture was degassed by purging with high-purity nitrogen for 10 min. An ice bath was used to maintain the reaction temperature. The mixture was stirred in the dark at 0 \u0026deg;C for half an hour to achieve adsorption-desorption equilibrium. The photocatalytic reaction was then initiated by irradiating the dispersion from the side with the LED lamps. During the reaction, a solution of styrene \u003cb\u003e1\u003c/b\u003e (0.5 mmol) in 2.0 mL HFIP was added using a syringe pump (at a rate of 4.0 mL/h). The remaining steps are the same as the general procedure.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDetails for the intramolecular [2\u0026thinsp;+\u0026thinsp;2] reactions.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo a solution of styrene \u003cb\u003e5\u003c/b\u003e (0.3 mmol) in 2.0 mL of HFIP, Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (10 mol%) was added in one portion. The remaining steps are the same as the general procedure.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDetails for the Diels\u0026ndash;Alder cycloadditions.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo a solution of the diene \u003cb\u003e7\u003c/b\u003e (2.0 mmol, 2.0 eq) in 2.0 mL of HFIP was added Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (8 mol%). Then, the reaction mixture was degassed by purging with high-purity nitrogen for 10 min. An ice bath was used to maintain the reaction temperature. The mixture was then stirred in the dark at 0 \u0026deg;C for half an hour to achieve adsorption-desorption equilibrium. The photocatalytic reaction was initiated by irradiating the dispersion from the side with an LED lamp. During the reaction, a solution of styrene \u003cb\u003e1\u003c/b\u003e (1.0 mmol) in 2.0 mL of HFIP was added using a syringe pump (at a rate of 4.0 mL/h). The remaining steps are the same as the general procedure.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe authors declare that all relevant data supporting the findings of this study are available either within the manuscript itself and/or in the Supplementary Information. Experimental details and characterization of products are provided in the Supplementary Information. All other data are available from the corresponding author upon request.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the National Natural Science Foundation of China (Grant Nos 22276112, 21922605, 22076007), the Natural Science Foundation of Shandong Province (Nos. 2019GSF109065, 2021CXGC011202 and ZR2019ZD45), the Taishan Scholar Project 454 Foundation of Shandong Province (No ts20190908) for the financial supports.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY.W., C.H. conceived the idea and directed the project. L.G. performed the experiments and analyzed the data. R.C., X.H., Y.L., and H.L., D.M. participated in characterization studies. G.W. performed the DFT calculation. Y.W. and L.G. wrote the manuscript, and L.G. prepared the Supplementary Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eNair, V.,Rajan, R.,Mohanan, K. \u0026amp; Sheeba, V. Cerium(iv) ammonium nitrate-mediated oxidative rearrangement of cyclobutanes and oxetanes. Tetrahedron Lett. 44, 4585\u0026ndash;4588 (2003).\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eYu, Y.,Fu, Y. \u0026amp; Zhong, F. Benign catalysis with iron: Facile assembly of cyclobutanes and cyclohexenes via intermolecular radical cation cycloadditions. Green Chem. 20, 1743\u0026ndash;1747 (2018).\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eColomer, I.,Coura Barcelos, R. \u0026amp; Donohoe, T. J. 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Phys. 13, 10071\u0026ndash;10075 (2011).\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes 1-2 are available in the Supplementary Files section.\u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"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-3026923/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3026923/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePhotocatalytic redox is an important method for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here we report that Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e nanoparticles (NPs) can efficiently catalyze intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable, and can be scaled up using sunlight. Mechanistic studies indicate that visible-light irradiation on Ag\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e NPs generates holes with high oxidation power, which effectively oxidize styrene adsorbates into radical cations. In photoreduced NPs, the conduction band electron (\u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e) has low reduction power due to the delocalization among the Ag\u003csup\u003e+\u003c/sup\u003e-lattices, while the NP surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with \u003cem\u003ee\u003c/em\u003e\u003csub\u003eCB\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e. Anethole radical cation\u003cstrong\u003e \u003c/strong\u003eon the NP’s surfaces has a lifetime of several hours, 10\u003csup\u003e8\u003c/sup\u003e times longer than in the homogeneous systems. The reaction between an adsorbed styrene molecule and a radical cation, the rate-limiting step, is greatly accelerated. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight.\u003c/p\u003e","manuscriptTitle":"Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-06-20 20:55:32","doi":"10.21203/rs.3.rs-3026923/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"fdec0c59-fd5a-4f69-9f45-586c90cdb81c","owner":[],"postedDate":"June 20th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":22453386,"name":"Physical sciences/Chemistry/Photochemistry/Photocatalysis"},{"id":22453387,"name":"Physical sciences/Chemistry/Physical chemistry/Excited states"}],"tags":[],"updatedAt":"2024-02-02T08:23:24+00:00","versionOfRecord":{"articleIdentity":"rs-3026923","link":"https://doi.org/10.1038/s41467-024-45217-y","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2024-02-01 05:00:00","publishedOnDateReadable":"February 1st, 2024"},"versionCreatedAt":"2023-06-20 20:55:32","video":"","vorDoi":"10.1038/s41467-024-45217-y","vorDoiUrl":"https://doi.org/10.1038/s41467-024-45217-y","workflowStages":[]},"version":"v1","identity":"rs-3026923","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3026923","identity":"rs-3026923","version":["v1"]},"buildId":"-HB7Z8yhvgn0wM9Nzuekk","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}