Copolyfluorenes containing polymethine dyes in the main chain: synthesis and photophysical properties

Copolyfluorenes containing polymethine dyes in the main chain: synthesis and photophysical properties | 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 Research Article Copolyfluorenes containing polymethine dyes in the main chain: synthesis and photophysical properties Elena V. Zhukova, Alexander M. Mitroshin, Ksenia I. Kaskevich, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6732791/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Oct, 2025 Read the published version in Journal of Polymer Research → Version 1 posted 5 You are reading this latest preprint version Abstract Despite the huge progress in the synthesis of small organic fluorophores and inorganic materials emitting in the red and near-infrared region, the synthesis of π-conjugated polymers with fluorescence in this range remains a challenging task. A series of fluorene-polymethine dye copolymers were synthesized by the Suzuki-Miyaura coupling polycondensation using cyanine, keto-cyanine, and squaraine comonomers, which exhibit fluorescence at ca. 500−700 nm. These polymers exhibit both green to red or near-infrared absorption and emission attributed to polymethine dyes, and absorption and emission bands corresponding to polyfluorene (at ca. 380 and 420−470 nm, respectively). The influence of pH on the UV-Vis absorption and luminescence spectra of the copolymers in solution was studied. Copolyfluorenes Cyanine dyes Fluorescence pH-sensitivity Polymethine dyes Squaraine dyes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Polymethine dyes are increasingly finding their use for optical sensors, solar cells, biometric authentication, optical communication, artificial intelligence, 3D imaging, etc . [ 1 – 5 ] One of the most important applications of such dyes is optical pH determination [ 6 ]. Intracellular pH is important for the diagnosis of several diseases. A wide variety of renal conditions, asthma, cystic fibrosis, solid tumors, and etc. cause an increase in the acidity of the environment. Therefore, the development of new sensors capable of rapid and exact monitoring of pH changes inside cells and tissues is a very important issue. Near-infrared (NIR) probes are considered as powerful tools and have been widely utilized for the detection of acidic tumor environments and monitoring pH changes in vivo . Operating in the NIR region has such advantages as deep tissue penetration, low background fluorescence and low risk of photodamage during irradiation [ 7 ]. Another distinctive advantage is the relatively low energy required to promote molecular excitation. Inexpensive diode laser sources can be used to excite NIR fluorogenic compounds [ 8 ]. Due to their excellent spectral and physical properties, polymethine dyes have attracted immense interest and have been employed as fluorescent labels and biosensors for in vivo imaging [ 9 , 10 ], theranostic agents [ 11 – 13 ], detection of analytes [ 14 , 15 ], peptide aggregation [ 16 , 17 ], protein staining [ 18 , 19 ], DNA and RNA labeling [ 20 , 21 ], sensing of viruses [ 22 ], and photosensitizers [ 23 , 24 ]. A series of studies are devoted to the synthesis of polymers with polymethine dyes and the study of their photophysical properties, pH sensitivity and photostability [ 25 – 27 ]. Among such polymers, conjugated ones are of greatest interest. Semiconducting polymer dots (Pdots) based on conjugated polymers are a class of highly fluorescent probes that possess extraordinary brightness, fast emission rates, good photostability, and minimal toxicity to biological cells and tissues. Recently, efforts have been made to develop Pdots with NIR emitting polymethine dyes as fluorescent probes. A range of fluorescent copolymers containing fluorene and polymethine units were synthesized and used as Pdots that show large Stokes shifts and narrow-band emissions in the NIR region [ 25 – 30 ]. In this work, we obtained a series of pH-sensitive copolyfluorenes containing polymethine dyes in the main chain. The resulting copolyfluorenes show a reversible pH response upon transition from alkaline to acidic media. These pH-sensitive copolymers exhibit several useful features: chemically incorporating the pH probe into the backbone of the hydrophobic conjugated polymers prevents the possibility of dye leakage; in the luminescence spectra of copolymer solutions, blue emission from polyfuorene (not pH-sensitive) and NIR emission from the polymethine dyes (pH-sensitive) are observed; by introducing additional fluorophores, it is possible to achieve efficient Förster resonance energy transfer from fluorene to polymethine dye fragments in the polymer chain. Experimental Materials All reagents and starting materials were purchased from commercial suppliers and used without further purification. Toluene (99%, Sigma-Aldrich, St. Louis, MI, USA) was distilled twice over sodium. Deionized water was obtained from a water purification system (RiOs-DI 3 Smart, Millipore, Merck, Darmstadt, Germany). All other solvents were purified by standard methods. Silica gel 60 (0.2–0.5 mm, Macherey-Nagel, Duren, Germany) underwent column chromatography and QuadraSil™ metal scavenger (20–100 micron, Alfa-Aesar, Ward Hill, MA, USA) was applied to remove Pd residuals. Instruments and measurements The polycondensation reactions were performed in the CEM Discover LabMate single-mode microwave reactor (CEM Corporation, Matthews, NC, USA) at a radiation frequency of 2.45 GHz and a maximum generator power of 300 W. The temperature of synthesis was controlled using an infrared sensor placed under the reaction vessel. Polymer films were prepared on an Ossila spin coater and dried or heated in a UT-4620 drying chamber. The CPF films were formed by spin coating on the glass from polymers solutions in toluene (200–220 µL). The toluene solution concentration was 10 mg/mL. The UV-visible absorption spectra were recorded on a Shimadzu UV-1900 spectrophotometer. Photoluminescence spectra were measured using an RF-6000 spectrofluorimeter. For studying luminescence and absorption spectra in solution, a 0.02 mg/mL concentration of each corresponding CPFPM in chloroform was chosen. The absorption and emission spectra of the films were measured immediately before heating and then after exposure for 4 h in the drying chamber at 80 °C and a high ventilation mode. FT-IR spectra were recorded on a Shimadzu IR Affinity-1S spectrometer using a Quest single-reflection ATR accessory (Specac), KRS-5 prism, 7800–400 cm − 1 range. Synthesis and characterization of materials Synthesis of polymethine dyes Polymethine dyes were synthesized according to previously published methods [ 31 – 35 ]. The synthetic procedures used are described in the Supplementary Materials. Synthesis of copolyfluorenes containing polymethine dyes The cylindrical reaction vessel was charged with 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester (0.1647 g, 0.25625 mmol), dibromo monomers, and triphenylphosphine (5 mg, 0.019 mmol). The Pd(PPh 3 ) 4 catalyst (6 mg, 0.005 mmol, 1 mol%) was added under argon atmosphere. Then, 2.5 mL of toluene, 2 mL of 2 M K 2 CO 3 solution, and methyltrioctylammonium chloride (Aliquat® 336) (10 mg, 0.019 mmol) in 1 mL of toluene, all three initially bubbled with moderate argon flow for 1 h, were loaded into the reaction vessel. The reaction vessel with a reflux condenser was placed in a microwave reactor, and the reaction mixture was stirred at an average of 90 °C (radiation power 80 W) for 1.5 h. Then, the additional portion of 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester (13 mg in 1 mL of toluene, 0.02 mmol) was added to the reaction mixture and after heating for another 1 h the end-capping reagent 4-bromophenyl ethyl ether (15 µL in 1 mL of toluene, 0.1 mmol) was added to the reaction mixture. Stirring and heating continued for another 1.5 h and the resulting two-phase mixture was cooled down to room temperature and poured into excess of methanol to form a precipitate. The resulting precipitate was washed with water twice, then with methanol, dried, redissolved in CHCl 3 , passed through a small column of metal-scavenger silica gel, and reprecipitated in methanol. Low-molecular mass fractions of polymer were extracted with acetone. Then, the precipitate was dissolved in CHCl 3 , filtered through Chromafil® Xtra PET-45/25 syringe filter, and reprecipitated in methanol. The yields of the CPFs after purification were 40–60%. The FT-IR, UV-vis, and luminescence spectra of the synthesized compounds are given in the Supplementary Materials, Figures S10−S32. Results and discussion Copolyfluorenes containing polymethine dyes in the main chain were synthesized by the Suzuki − Miyaura cross-coupling reaction of 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester with a mixture of 2,7-dibromo-9,9-dioctyl-9H-fluorene with a polymethine dye dibromide derivative (PMBr 2 ), and, optionally, 4,7-dibromo-2,1,3-benzothiadiazole (BTBr 2 ), using microwave irradiation (80 W) in an inert atmosphere at 90 °C (Fig. 1). The reaction was carried out using [Pd(PPh 3 ) 4 ] as a catalyst in the presence of PPh 3 , K 2 CO 3 and Aliquat® 336 in a toluene/water biphasic medium. Cyanine, keto-cyanine, and squaraine comonomers were used for the synthesis of copolyfluerenes (CPFPMs). Additionally to fluorene and polymethine-containing units, CPFPM2 contains a benzothiadiazole luminophore, which enhances the efficiency of Förster energy transfer from fluorene to polymethine moiety [36, 37]. The polymers had weight-average molecular masses (M w ) of 17.0 to 91.2 kDa, number-average molecular masses (M n ) of 10.6 to 78.0 kDa and polydispersity indexes (PDI = M w /M n ) of 1.3–2.7. Detailed molecular weight data are summarized in Table 2. Table 2 Molecular mass 1 characteristics of copolyfluorenes Polymer M w , kDa M n , kDa PDI CPFPM1 64.1 30.5 2.1 CPFPM2 31.3 15.7 2.0 CPFPM3 61.3 30.3 2.0 CPFPM4 81.0 29.7 2.7 CPFPM5 99.7 78.0 1.3 1 LS detector data presented. The IR spectral data for the synthesized compounds are given in the Supporting Information, Figures S10−S14. CPFPMs absorb at 2920 and 2850 cm −1 due to C−H stretching vibrations and at 1450 cm − 1 due to C = C Ar stretching vibrations. The IR spectrum of CPFPM3 also contains a band at 1720 cm −1 corresponding to C = O stretching vibrations. In the IR spectra of CPFPM4 and CPFPM5, bands of the C = O conjugated bond stretching vibrations are observed at 1610 cm −1 . The polymers are well soluble in chloroform and toluene. The polymeric films for photophysical studies were formed by spin coating on the glass plate from polymer solutions in toluene. UV-vis absorption and fluorescence characteristics of CPFPMs The UV-Vis absorption spectra of CPFPMs were measured in chloroform solution and film (Table 3 and Supporting Information, Figures S15, S16, S18, S19, S21−S23, S26, S27, S29, S30, and S32). They show a band at 380−400 nm attributed to the π−π* transition in the polyfluorene backbone and a band at 550−690 nm, which belongs to polymethine dyes. In the UV-Vis spectrum of CPFPM5, the polymethine dye band has a blue-shifted shoulder at 625 and 628 nm in solution and film, respectively (Figs. 2, 3). Additionally, the UV-Vis spectrum of CPFPM2 contains bands at 440 and 465 nm corresponding to the π−π* transition in the benzothiadiazole unit in solution and in the solid state, respectively (Supporting Information, Figures S19 and S21). The fluorescence spectra of CPFPMs in chloroform solution revealed emissions at 416, 440, and 471 nm assigned to the polyfluorene fragments and at 530−700 nm, usually with a red-shifted shoulder, attributed to polymethine dyes (Table 3 and Supporting Information, Figures S17, S20, S24, S25, S28, and S31). The presence of a shoulder in the luminescence spectrum is characteristic for polymethine dyes and usually associated with their aggregation. The fluorescence spectrum of CPFPM2 in chloroform contains a band at 557 nm associated with benzothiadiazole fragments, in addition to bands attributed to fluorene and polymethine units (Table 3 and Supporting Information, Figure S20). The fluorescence spectra of CPFPMs in the film have a more intense band of the polymethine dye relative to the emission bands of polyfluorene compared to the spectra in a chloroform solution, which is caused by a more efficient energy transfer from polyfluorene to the polymethine fragment due to aggregation in the solid phase (Figs. 3, 4 and Supporting Information, Figures S18, S21, S26, S29, and S32). Table 3 Photophysical characteristics of CPFPMs (λ ex = 385 nm) Polymer λ abs , nm λ em , nm λ abs , nm λ em , nm chloroform solution film CPFPM1 388, 680 418, 440, 471* 385 430, 455, 485*, 710 CPFPM2 385, 440* 417, 440, 471*, 557, 620* 387, 424*, 465*, 601 418*, 436, 532, 682* CPFPM3 390, 437, 474, 555, 757 417, 440, 471 385 433, 460, 492, 533 CPFPM4 389, 670 417, 440, 471*, 683 383, 625*, 680 434, 460, 489, 693, 747* CPFPM5 386, 625*, 670 417, 440, 471*, 691, 746* 379, 628*, 679 416, 437, 469*, 705 * Shoulder The influence of acid and base additives on the photophysical properties of CPFPMs The effect of pH on the absorption and emission spectra of CPFPMs in a chloroform solution was studied. We have compared the spectra of CPFPMs in pure chloroform and in the presence of trifluoroacetic acid (TFA, 0.022 M) and triethylamine (TEA, 0.24 M) in chloroform solutions (Supporting Information, Figures S15−S17, S19, S20, S22−S25, S27, S28, S30, and S31). The addition of TFA and TEA to the CPFPM1 solution has practically no effect on the UV absorption and luminescence spectra (Supporting Information, Figures S15−S17). Also, no changes were observed in the UV-Vis absorption spectrum of the CPFPM2 solution upon the addition of acid and base (Supporting Information, Figure S19). However, in the luminescence spectrum of CPFPM2 (Fig. 4), the intensity of the band of 2,1,3-benzothiadiazole at 557 nm decreases with the addition of acid (Supporting Information, Figures S20 and S33). Interestingly, the acid doesn’t influence luminescence of 2,1,3-benzothiadiazole solution, but strongly affects the photophysical properties of CPFPM2. A good fit linear relation between the integral fluorescence intensity of the long-wavelength band and the logarithm of the TFA concentration was observed (Supporting Information, Figure S33). For an acidic solution of CPFPM3, the absorption band of the dye is blue-shifted from 757 to 563 nm (Supporting Information, Figure S23). Due to the absorption of fluorene in the region of 380−450 nm, the solution in an acidic medium is colored blue-violet. The long-wavelength band in the UV-Vis absorption spectrum of CPFPM3 in a chloroform solution with the addition of TEA is located at 550 nm. The luminescence spectrum of the acidic solution of CPFPM3 shows a band at 750 nm, while the addition of TEA results in the appearance of a band at 618 nm (Supporting Information, Figure S25). Since polymers CPFPM4 and CPFPM5 have a similar nature and differ only in the content of squaraine dye, the UV-Vis and luminescence spectra of their solutions in chloroform have the same bands, but the squaraine dye bands have higher intensities in the spectra of CPFPM5 (Supporting Information, Figures S27, S28, S30, and S31). The influence of acid and base additives on the UV-Vis and luminescence spectra was studied for CPFPM5 in chloroform solution (Supporting Information, Figures S28 and S31). The addition of TEA does not lead to significant changes in the absorption and emission spectra of CPFPM5. However, the intensity of the absorption and emission bands of the squaraine dye (670 and 691 nm, respectively) decreases upon the addition of TFA (Fig. 5 and Supporting Information, Figures S34−S36). The graph of the dependence of fluorescence intensity on the logarithm of the concentration of trifluoroacetic acid has two linear regions with different slopes (Supporting Information, Figure S35). This is due to the possibility of protonation of two oxygen atoms of the squaraine ring. Thus, copolyfluorenes with ketocyanine and squaraine units are promising materials for pH determination, especially in acidic media. Aggregation of molecules leads to a significant enhancement of the polymethine dye band in the emission spectra. Conclusion In summary, we have synthesized a series of copolyfluorenes containing polymethine dyes with absorption and emission from violet to red region. Their photophysical properties were studied both in solution and in the solid state. A hyperchromic effect is observed for the emission band of the polymethine unit of CPFPMs in the film compared to the chloroform solution, which is due to the aggregation induced emission. The influence of acid (TFA) and base (TEA) on UV-Vis absorption and emission spectra was also considered. The absorption and fluorescence spectra of CPFPM3 show changes in the presence of both TFA and TEA. For CPFPM2, CPFPM4 and CPFPM5, the intensity of the polymethine dye band in the emission spectra was most clearly reduced by the addition of TFA. The acidity has the greatest effect on the fluorescence spectrum of CPFPM5. The incorporation of polymethine dyes, especially ketocyanine and squaraine into polymers has provided opportunities for rapid and efficient pH determination in non-aqueous media. On the other hand, the presence of fluorene in the polymer chain leads to an increase in the fluorescence intensity of polymethine units in the red and NIR regions, which is most strongly manifested in the aggregated state. Thus, the synthesis and study of the properties of copolymers based on polymethine dyes is of considerable interest for the development of new luminescent materials, Pdots, and chemosensors. Declarations Acknowledgements The work was funded by the National Research Center “Kurchatov Institute” under the state assignment № 1023031700043-2-1.4.4. Author contributions Elena V. Zhukova: Investigation (lead). Alexander M. Mitroshin: Investigation (supporting). Ksenia I. Kaskevich: Investigation (supporting). Serguei A. Miltsov: Investigation (lead); formal analysis (lead). Larisa S. Litvinova: Investigation (supporting). Tatiana G. Chulkova: Data curation (supporting); formal analysis (lead); writing – original draft (lead). Alexander V. Yakimansky: Data curation (lead); formal analysis (lead); resources (lead); supervision (lead); writing – review and editing (lead). Funding The National Research Center “Kurchatov Institute”, state assignment № 1023031700043-2-1.4.4. Data availability Data sharing does not apply to this article as no datasets were generated or analyzed during the current study. Conflict of interest The authors declare no conficts of interest. References Ou YF, Ren TB, Yuan L, Zhang XB (2023) Molecular Design of NIR-II Polymethine Fluorophores for Bioimaging and Biosensing. Chem Biomed Imaging 1:220–233. https://doi.org/10.1021/cbmi.3c00040 Gastaldi M, Cardano F, Zanetti M, et al (2021) Functional Dyes in Polymeric 3D Printing: Applications and Perspectives. ACS Mater Lett 3:1–17. https://doi.org/10.1021/acsmaterialslett.0c00455 Ilina K, MacCuaig WM, Laramie M, et al (2020) Squaraine Dyes: Molecular Design for Different Applications and Remaining Challenges. Bioconjug Chem 31:194–213. https://doi.org/10.1021/acs.bioconjchem.9b00482 Shindy HA (2017) Fundamentals in the chemistry of cyanine dyes: A review. Dye Pigment 145:505–513. https://doi.org/10.1016/j.dyepig.2017.06.029 Bifari EN, Almeida P, El-Shishtawy RM (2023) Advancing panchromatic effect for efficient sensitization of cyanine and hemicyanine-based dye-sensitized solar cells. Mater Today Energy 36:101337. https://doi.org/10.1016/j.mtener.2023.101337 Sun W, Guo S, Hu C, et al (2016) Recent Development of Chemosensors Based on Cyanine Platforms. Chem Rev 116:7768–7817. https://doi.org/10.1021/acs.chemrev.6b00001 Kelderhouse LE, Chelvam V, Wayua C, et al (2013) Development of Tumor-Targeted Near Infrared Probes for Fluorescence Guided Surgery. Bioconjug Chem 24:1075–1080. https://doi.org/10.1021/bc400131a Zhang H, Yan C, Li H, et al (2021) Rational Design of Near-Infrared Cyanine-Based Fluorescent Probes for Rapid In Vivo Sensing Cysteine. ACS Appl Bio Mater 4:2001–2008. https://doi.org/10.1021/acsabm.0c00260 Gamage RS, Li D-H, Schreiber CL, Smith BD (2021) Comparison of cRGDfK Peptide Probes with Appended Shielded Heptamethine Cyanine Dye ( s775z ) for Near Infrared Fluorescence Imaging of Cancer. ACS Omega 6:30130–30139. https://doi.org/10.1021/acsomega.1c04991 Yang Z, Sun Q, Ji L, et al (2025) Recent Advances for Synthesis and Bioapplications of Polymethine Cyanines. Asian J Org Chem. https://doi.org/10.1002/ajoc.202500109 Liu Q, Ding X, Xu X, et al (2022) Tumor-targeted hyaluronic acid-based oxidative stress nanoamplifier with ROS generation and GSH depletion for antitumor therapy. Int J Biol Macromol 207:771–783. https://doi.org/10.1016/j.ijbiomac.2022.03.139 Yang Z-C, Gu Q-S, Chao J-J, et al (2024) Glutathione-activated biotin-targeted dual-modal imaging probe with improved PDT/PTT synergistic therapy. Anal Chim Acta 1316:342860. https://doi.org/10.1016/j.aca.2024.342860 Xu Y, Meng X, Zhao Y, et al (2024) Pyrrolopyrrole Cyanine J-Aggregate Nanoparticles with High Near-Infrared Fluorescence Brightness and Photothermal Performance for Efficient Phototheranostics. ACS Appl Mater Interfaces 16:39005–39020. https://doi.org/10.1021/acsami.4c06225 Cao C, Zhou X, Xue M, et al (2019) Dual Near-Infrared-Emissive Luminescent Nanoprobes for Ratiometric Luminescent Monitoring of ClO – in Living Organisms. ACS Appl Mater Interfaces 11:15298–15305. https://doi.org/10.1021/acsami.9b02008 Wang R, Han X, You J, et al (2018) Ratiometric Near-Infrared Fluorescent Probe for Synergistic Detection of Monoamine Oxidase B and Its Contribution to Oxidative Stress in Cell and Mice Aging Models. Anal Chem 90:4054–4061. https://doi.org/10.1021/acs.analchem.7b05297 Shahane SD, Mudliar NH, Chawda BR, et al (2025) YOPRO-1: A Cyanine-Based Molecular Rotor Probe for Amyloid Fibril Detection. ACS Appl Bio Mater 8:3443–3453. https://doi.org/10.1021/acsabm.5c00186 Li Y, Chen C, Xu D, et al (2018) Effective Theranostic Cyanine for Imaging of Amyloid Species in Vivo and Cognitive Improvements in Mouse Model. ACS Omega 3:6812–6819. https://doi.org/10.1021/acsomega.8b00475 Bai L, Jia Y, Wang Z, et al (2025) Albumin Encapsulation of Cyanine Dye for High-Performance NIR-II Imaging-Guided Photodynamic Therapy. Chem Biomed Imaging. https://doi.org/10.1021/cbmi.5c00005 Jiang S, Li W, Li B, et al (2025) Albumin-Energized NIR-II Cyanine Dye for Fluorescence/Photoacoustic/Photothermal Multi-Modality Imaging-Guided Tumor Homologous Targeting Photothermal Therapy. J Med Chem 68:3324–3334. https://doi.org/10.1021/acs.jmedchem.4c02369 Sun H, Sun R, Yang D, et al (2024) A Cyanine Dye for Highly Specific Recognition of Parallel G-Quadruplex Topology and Its Application in Clinical RNA Detection for Cancer Diagnosis. J Am Chem Soc 146:22736–22746. https://doi.org/10.1021/jacs.4c07698 Nano A, Boynton AN, Barton JK (2017) A Rhodium-Cyanine Fluorescent Probe: Detection and Signaling of Mismatches in DNA. J Am Chem Soc 139:17301–17304. https://doi.org/10.1021/jacs.7b10639 Saarnio VK, Salorinne K, Ruokolainen VP, et al (2020) Development of functionalized SYBR green II related cyanine dyes for viral RNA detection. Dye Pigment 177:108282. https://doi.org/10.1016/j.dyepig.2020.108282 Pontremoli C, Chinigò G, Galliano S, et al (2023) Photosensitizers for photodynamic therapy: Structure-activity analysis of cyanine dyes through design of experiments. Dye Pigment 210:111047. https://doi.org/10.1016/j.dyepig.2022.111047 Rozovsky A, Patsenker L, Gellerman G (2019) Bifunctional reactive pentamethine cyanine dyes for biomedical applications. Dye Pigment 162:18–25. https://doi.org/10.1016/j.dyepig.2018.09.064 Chen L, Wu L, Yu J, et al (2017) Highly photostable wide-dynamic-range pH sensitive semiconducting polymer dots enabled by dendronizing the near-IR emitters. Chem Sci 8:7236–7245. https://doi.org/10.1039/C7SC03448B Verma M, Chan Y-H, Saha S, Liu M-H (2021) Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging. ACS Appl Bio Mater 4:2142–2159. https://doi.org/10.1021/acsabm.0c01185 Chen Y-H, Kuo S-Y, Tsai W-K, et al (2016) Dual Colorimetric and Fluorescent Imaging of Latent Fingerprints on Both Porous and Nonporous Surfaces with Near-Infrared Fluorescent Semiconducting Polymer Dots. Anal Chem 88:11616–11623. https://doi.org/10.1021/acs.analchem.6b03178 Wu I-C, Yu J, Ye F, et al (2015) Squaraine-Based Polymer Dots with Narrow, Bright Near-Infrared Fluorescence for Biological Applications. J Am Chem Soc 137:173–178. https://doi.org/10.1021/ja5123045 Li X, Chen H, Su Z, et al (2024) Brightness Strategies toward NIR-II Emissive Conjugated Materials: Molecular Design, Application, and Future Prospects. ACS Appl Bio Mater 7:8019–8039. https://doi.org/10.1021/acsabm.4c00137 Lawrance R, Chowdhury P, Lin H-C, Chan Y-H (2024) The luminous frontier: transformative NIR-IIa fluorescent polymer dots for deep-tissue imaging. RSC Appl Polym 2:749–774. https://doi.org/10.1039/D4LP00076E Reddington M V. (2007) Synthesis and Properties of Phosphonic Acid Containing Cyanine and Squaraine Dyes for Use as Fluorescent Labels. Bioconjug Chem 18:2178–2190. https://doi.org/10.1021/bc070090y Lloyd D, McNab H, Marshall DR (1973) Diazepines; XVII 1 . Simple Preparation of 2,3-Dihydro-1 H -1,4-diazepinium Perchlorate. Synthesis (Stuttg) 1973:791–791. https://doi.org/10.1055/s-1973-22305 Lindsey JS, Brown PA, Siesel DA (1989) Visible light-harvesting in covalently-linked porphyrin-cyanine dyes. Tetrahedron 45:4845–4866. https://doi.org/10.1016/S0040-4020(01)85156-5 Miltsov S, Goikhman M, Yakimansky A, et al (2019) N-Bromosuccinimide-mediated dimerization of unsymmetrical indodicarbocyanine dyes. Tetrahedron Lett 60:151005. https://doi.org/10.1016/j.tetlet.2019.151005 Slominskii YL, Radchenko ID, Popov S V., Tolmachev AI (1983) Polymethine dyes with hydrocarbon bridges. Enamine ketones in the chemistry of cyanine dyes. Zh Org Khim 19:2134–2142 Smyslov RY, Tomilin FN, Shchugoreva IA, et al (2019) Synthesis and photophysical properties of copolyfluorenes for light-emitting applications: Spectroscopic experimental study and theoretical DFT consideration. Polymer (Guildf) 168:185–198. https://doi.org/10.1016/j.polymer.2019.02.015 Yevlampieva NP, Khurchak AP, Nosova GI, et al (2016) Chain microstructure and specific features of excitation energy transfer in solution and films of poly(9,9-dioctylfluorene) doped with 2,1,3-benzothiadiazole comonomer units. Chem Phys Lett 645:100–105. https://doi.org/10.1016/j.cplett.2015.12.039 Table 1 Table 1 is available in the Supplementary Files section. Supplementary Files Table1.docx SupportingInformationcyanine.docx Cite Share Download PDF Status: Published Journal Publication published 09 Oct, 2025 Read the published version in Journal of Polymer Research → Version 1 posted Reviewers agreed at journal 09 Jul, 2025 Reviewers invited by journal 09 Jul, 2025 Editor invited by journal 18 Jun, 2025 Editor assigned by journal 29 May, 2025 First submitted to journal 28 May, 2025 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-6732791","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482785960,"identity":"5f864808-a38f-4563-bb44-64a17f8585d0","order_by":0,"name":"Elena V. Zhukova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Elena","middleName":"V.","lastName":"Zhukova","suffix":""},{"id":482785961,"identity":"63fea951-cb1e-4514-b26b-df2a0a5cf7f4","order_by":1,"name":"Alexander M. Mitroshin","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Alexander","middleName":"M.","lastName":"Mitroshin","suffix":""},{"id":482785962,"identity":"1d142084-467a-4c2f-961d-51be7fee7e04","order_by":2,"name":"Ksenia I. Kaskevich","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Ksenia","middleName":"I.","lastName":"Kaskevich","suffix":""},{"id":482785963,"identity":"cdd016e5-ab18-4a32-9f5e-124223d1684f","order_by":3,"name":"Serguei A. Miltsov","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Serguei","middleName":"A.","lastName":"Miltsov","suffix":""},{"id":482785964,"identity":"03f6b461-8ba5-4bf0-a9a2-ebc445251728","order_by":4,"name":"Larisa S. Litvinova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Larisa","middleName":"S.","lastName":"Litvinova","suffix":""},{"id":482785965,"identity":"198edccb-a3e3-467b-8ab1-575aabf59618","order_by":5,"name":"Tatiana G. Chulkova","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Tatiana","middleName":"G.","lastName":"Chulkova","suffix":""},{"id":482785966,"identity":"0806bc27-04a2-4b42-97a5-9293af5de880","order_by":6,"name":"Alexander V. Yakimansky","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5ElEQVRIiWNgGAWjYFACNoYDIEqCgfkAA2MDaVrYEojXwgDRwmNAnBaD48cSD92ouWMvOSPnm8TPHTZyDOyHj27Aq+VM2oHDOceeJc6WyN0m2XsmzZiBJy3tBl4tB9IbDuewHU6QA2qR4G07nNggwWOGX8v550At/w7by0nkPJP8S5SWG0CH5bYdZpwtkcMmTZQtkjeeJRzO7TucOLPnmbG1bFuaMRshv/CdTzP+nPPtsL3E8eSHN9+22cjxsx8+hleLwgEYSyCBRQJEs+FTDgLyDTAW/wHmD4RUj4JRMApGwcgEAN7kU8MpRBDMAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-8770-1453","institution":"Institute of Macromolecular Compounds of the Russian Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Alexander","middleName":"V.","lastName":"Yakimansky","suffix":""}],"badges":[],"createdAt":"2025-05-23 12:21:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6732791/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6732791/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10965-025-04608-5","type":"published","date":"2025-10-09T15:57:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86535089,"identity":"dd555bd6-c81e-487e-9e86-0972a935c91c","added_by":"auto","created_at":"2025-07-11 18:11:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":160000,"visible":true,"origin":"","legend":"\u003cp\u003eSynthesis of copolyfluorenes with polymethine moieties\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/99fb0a0ac0cf457a4aca3f6e.png"},{"id":86534269,"identity":"589325df-76ab-497f-93ef-32592cfd9d5b","added_by":"auto","created_at":"2025-07-11 18:03:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":237200,"visible":true,"origin":"","legend":"\u003cp\u003eThe UV-Vis spectra of \u003cstrong\u003eCPFPM5 \u003c/strong\u003ein chloroform (black line), in chloroform with TFA (red line)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/d663f9e88f0b9560f1b44bc9.png"},{"id":86534272,"identity":"c267c3cd-e2f9-40c9-b7e6-d492fd61769a","added_by":"auto","created_at":"2025-07-11 18:03:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":324700,"visible":true,"origin":"","legend":"\u003cp\u003eThe UV-Vis absorption and fluorescence spectra of \u003cstrong\u003eCPFPM5 \u003c/strong\u003ein film (blue and black lines, respectively)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/224bf485652737c7d378925a.png"},{"id":86534270,"identity":"503ab2a3-9d1b-44ab-9d4f-476c4a0977a8","added_by":"auto","created_at":"2025-07-11 18:03:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":499394,"visible":true,"origin":"","legend":"\u003cp\u003eThe fluorescence response of \u003cstrong\u003eCPFPM2 \u003c/strong\u003ein chloroform solution upon addition of TFA\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/4d7c6317d14dac809cd0981d.png"},{"id":86535091,"identity":"d30af927-635a-4bb6-9ab1-5792398e9d67","added_by":"auto","created_at":"2025-07-11 18:11:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":406310,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence spectra of \u003cstrong\u003eCPFPM5 \u003c/strong\u003ein chloroform changed with the different concentrations of TFA\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/d8355a46ef88b7c07f93fd14.png"},{"id":93420022,"identity":"d5244c02-f2a9-4a0e-861d-e509542678d1","added_by":"auto","created_at":"2025-10-13 16:09:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2123226,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/4e537a81-776c-42d9-b1c2-3ae62fb0b307.pdf"},{"id":86534264,"identity":"c81bad85-64bd-43ec-9bdf-16bc4e469826","added_by":"auto","created_at":"2025-07-11 18:03:51","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":108833,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/8619bd060e1de36b1667460b.docx"},{"id":86535432,"identity":"da913ddc-8467-4efd-b9b8-4227d97790c2","added_by":"auto","created_at":"2025-07-11 18:19:51","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1971341,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformationcyanine.docx","url":"https://assets-eu.researchsquare.com/files/rs-6732791/v1/efcfbb5f72798d5adad01d2e.docx"}],"financialInterests":"","formattedTitle":"Copolyfluorenes containing polymethine dyes in the main chain: synthesis and photophysical properties","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePolymethine dyes are increasingly finding their use for optical sensors, solar cells, biometric authentication, optical communication, artificial intelligence, 3D imaging, \u003cem\u003eetc\u003c/em\u003e. [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] One of the most important applications of such dyes is optical pH determination [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Intracellular pH is important for the diagnosis of several diseases. A wide variety of renal conditions, asthma, cystic fibrosis, solid tumors, and \u003cem\u003eetc.\u003c/em\u003e cause an increase in the acidity of the environment. Therefore, the development of new sensors capable of rapid and exact monitoring of pH changes inside cells and tissues is a very important issue. Near-infrared (NIR) probes are considered as powerful tools and have been widely utilized for the detection of acidic tumor environments and monitoring pH changes \u003cem\u003ein vivo\u003c/em\u003e. Operating in the NIR region has such advantages as deep tissue penetration, low background fluorescence and low risk of photodamage during irradiation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Another distinctive advantage is the relatively low energy required to promote molecular excitation. Inexpensive diode laser sources can be used to excite NIR fluorogenic compounds [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Due to their excellent spectral and physical properties, polymethine dyes have attracted immense interest and have been employed as fluorescent labels and biosensors for in vivo imaging [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], theranostic agents [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], detection of analytes [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], peptide aggregation [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], protein staining [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], DNA and RNA labeling [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], sensing of viruses [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], and photosensitizers [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. A series of studies are devoted to the synthesis of polymers with polymethine dyes and the study of their photophysical properties, pH sensitivity and photostability [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Among such polymers, conjugated ones are of greatest interest. Semiconducting polymer dots (Pdots) based on conjugated polymers are a class of highly fluorescent probes that possess extraordinary brightness, fast emission rates, good photostability, and minimal toxicity to biological cells and tissues. Recently, efforts have been made to develop Pdots with NIR emitting polymethine dyes as fluorescent probes. A range of fluorescent copolymers containing fluorene and polymethine units were synthesized and used as Pdots that show large Stokes shifts and narrow-band emissions in the NIR region [\u003cspan additionalcitationids=\"CR26 CR27 CR28 CR29\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this work, we obtained a series of pH-sensitive copolyfluorenes containing polymethine dyes in the main chain. The resulting copolyfluorenes show a reversible pH response upon transition from alkaline to acidic media. These pH-sensitive copolymers exhibit several useful features: chemically incorporating the pH probe into the backbone of the hydrophobic conjugated polymers prevents the possibility of dye leakage; in the luminescence spectra of copolymer solutions, blue emission from polyfuorene (not pH-sensitive) and NIR emission from the polymethine dyes (pH-sensitive) are observed; by introducing additional fluorophores, it is possible to achieve efficient F\u0026ouml;rster resonance energy transfer from fluorene to polymethine dye fragments in the polymer chain.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaterials\u003c/h2\u003e\u003cp\u003eAll reagents and starting materials were purchased from commercial suppliers and used without further purification. Toluene (99%, Sigma-Aldrich, St. Louis, MI, USA) was distilled twice over sodium. Deionized water was obtained from a water purification system (RiOs-DI 3 Smart, Millipore, Merck, Darmstadt, Germany). All other solvents were purified by standard methods. Silica gel 60 (0.2\u0026ndash;0.5 mm, Macherey-Nagel, Duren, Germany) underwent column chromatography and QuadraSil\u0026trade; metal scavenger (20\u0026ndash;100 micron, Alfa-Aesar, Ward Hill, MA, USA) was applied to remove Pd residuals.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eInstruments and measurements\u003c/h3\u003e\n\u003cp\u003eThe polycondensation reactions were performed in the CEM Discover LabMate single-mode microwave reactor (CEM Corporation, Matthews, NC, USA) at a radiation frequency of 2.45 GHz and a maximum generator power of 300 W. The temperature of synthesis was controlled using an infrared sensor placed under the reaction vessel. Polymer films were prepared on an Ossila spin coater and dried or heated in a UT-4620 drying chamber. The CPF films were formed by spin coating on the glass from polymers solutions in toluene (200\u0026ndash;220 \u0026micro;L). The toluene solution concentration was 10 mg/mL. The UV-visible absorption spectra were recorded on a Shimadzu UV-1900 spectrophotometer. Photoluminescence spectra were measured using an RF-6000 spectrofluorimeter. For studying luminescence and absorption spectra in solution, a 0.02 mg/mL concentration of each corresponding CPFPM in chloroform was chosen. The absorption and emission spectra of the films were measured immediately before heating and then after exposure for 4 h in the drying chamber at 80 \u0026deg;C and a high ventilation mode. FT-IR spectra were recorded on a Shimadzu IR Affinity-1S spectrometer using a Quest single-reflection ATR accessory (Specac), KRS-5 prism, 7800\u0026ndash;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range.\u003c/p\u003e\n\u003ch3\u003eSynthesis and characterization of materials\u003c/h3\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003eSynthesis of polymethine dyes\u003c/h2\u003e\u003cp\u003ePolymethine dyes were synthesized according to previously published methods [\u003cspan additionalcitationids=\"CR32 CR33 CR34\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The synthetic procedures used are described in the Supplementary Materials.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSynthesis of copolyfluorenes containing polymethine dyes\u003c/h3\u003e\n\u003cp\u003eThe cylindrical reaction vessel was charged with 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester (0.1647 g, 0.25625 mmol), dibromo monomers, and triphenylphosphine (5 mg, 0.019 mmol). The Pd(PPh\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e catalyst (6 mg, 0.005 mmol, 1 mol%) was added under argon atmosphere. Then, 2.5 mL of toluene, 2 mL of 2 M K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e solution, and methyltrioctylammonium chloride (Aliquat\u0026reg; 336) (10 mg, 0.019 mmol) in 1 mL of toluene, all three initially bubbled with moderate argon flow for 1 h, were loaded into the reaction vessel. The reaction vessel with a reflux condenser was placed in a microwave reactor, and the reaction mixture was stirred at an average of 90 \u0026deg;C (radiation power 80 W) for 1.5 h. Then, the additional portion of 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester (13 mg in 1 mL of toluene, 0.02 mmol) was added to the reaction mixture and after heating for another 1 h the end-capping reagent 4-bromophenyl ethyl ether (15 \u0026micro;L in 1 mL of toluene, 0.1 mmol) was added to the reaction mixture. Stirring and heating continued for another 1.5 h and the resulting two-phase mixture was cooled down to room temperature and poured into excess of methanol to form a precipitate.\u003c/p\u003e\u003cp\u003eThe resulting precipitate was washed with water twice, then with methanol, dried, redissolved in CHCl\u003csub\u003e3\u003c/sub\u003e, passed through a small column of metal-scavenger silica gel, and reprecipitated in methanol. Low-molecular mass fractions of polymer were extracted with acetone. Then, the precipitate was dissolved in CHCl\u003csub\u003e3\u003c/sub\u003e, filtered through Chromafil\u0026reg; Xtra PET-45/25 syringe filter, and reprecipitated in methanol. The yields of the CPFs after purification were 40\u0026ndash;60%. The FT-IR, UV-vis, and luminescence spectra of the synthesized compounds are given in the Supplementary Materials, Figures S10\u0026minus;S32.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eCopolyfluorenes containing polymethine dyes in the main chain were synthesized by the Suzuki − Miyaura cross-coupling reaction of 9,9-dioctyl-9H-fluorene-2,7-diboronic acid bis(pinacol) ester with a mixture of 2,7-dibromo-9,9-dioctyl-9H-fluorene with a polymethine dye dibromide derivative (PMBr\u003csub\u003e2\u003c/sub\u003e), and, optionally, 4,7-dibromo-2,1,3-benzothiadiazole (BTBr\u003csub\u003e2\u003c/sub\u003e), using microwave irradiation (80 W) in an inert atmosphere at 90 °C (Fig. 1). The reaction was carried out using [Pd(PPh\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e] as a catalyst in the presence of PPh\u003csub\u003e3\u003c/sub\u003e, K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and Aliquat® 336 in a toluene/water biphasic medium.\u003c/p\u003e\n\u003cp\u003eCyanine, keto-cyanine, and squaraine comonomers were used for the synthesis of copolyfluerenes (CPFPMs). Additionally to fluorene and polymethine-containing units, CPFPM2 contains a benzothiadiazole luminophore, which enhances the efficiency of Förster energy transfer from fluorene to polymethine moiety [36, 37]. The polymers had weight-average molecular masses (M\u003csub\u003ew\u003c/sub\u003e) of 17.0 to 91.2 kDa, number-average molecular masses (M\u003csub\u003en\u003c/sub\u003e) of 10.6 to 78.0 kDa and polydispersity indexes (PDI = M\u003csub\u003ew\u003c/sub\u003e/M\u003csub\u003en\u003c/sub\u003e) of 1.3–2.7. Detailed molecular weight data are summarized in Table 2.\u003c/p\u003e\n\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eMolecular mass\u003csup\u003e1\u003c/sup\u003e characteristics of copolyfluorenes\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePolymer\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eM\u003csub\u003ew\u003c/sub\u003e, kDa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eM\u003csub\u003en\u003c/sub\u003e, kDa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePDI\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e64.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e99.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\u003csup\u003e1\u003c/sup\u003e LS detector data presented.\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eThe IR spectral data for the synthesized compounds are given in the Supporting Information, Figures S10−S14. CPFPMs absorb at 2920 and 2850 cm\u003csup\u003e−1\u003c/sup\u003e due to C−H stretching vibrations and at 1450 cm\u003csup\u003e− 1\u003c/sup\u003e due to C = C\u003csub\u003eAr\u003c/sub\u003e stretching vibrations. The IR spectrum of CPFPM3 also contains a band at 1720 cm\u003csup\u003e−1\u003c/sup\u003e corresponding to C = O stretching vibrations. In the IR spectra of CPFPM4 and CPFPM5, bands of the C = O conjugated bond stretching vibrations are observed at 1610 cm\u003csup\u003e−1\u003c/sup\u003e. The polymers are well soluble in chloroform and toluene. The polymeric films for photophysical studies were formed by spin coating on the glass plate from polymer solutions in toluene.\u003c/p\u003e\n\u003ch3\u003eUV-vis absorption and fluorescence characteristics of CPFPMs\u003c/h3\u003e\n\u003cp\u003eThe UV-Vis absorption spectra of CPFPMs were measured in chloroform solution and film (Table 3 and Supporting Information, Figures S15, S16, S18, S19, S21−S23, S26, S27, S29, S30, and S32). They show a band at 380−400 nm attributed to the π−π* transition in the polyfluorene backbone and a band at 550−690 nm, which belongs to polymethine dyes. In the UV-Vis spectrum of CPFPM5, the polymethine dye band has a blue-shifted shoulder at 625 and 628 nm in solution and film, respectively (Figs. 2, 3). Additionally, the UV-Vis spectrum of CPFPM2 contains bands at 440 and 465 nm corresponding to the π−π* transition in the benzothiadiazole unit in solution and in the solid state, respectively (Supporting Information, Figures S19 and S21).\u003c/p\u003e\n\u003cp\u003eThe fluorescence spectra of CPFPMs in chloroform solution revealed emissions at 416, 440, and 471 nm assigned to the polyfluorene fragments and at 530−700 nm, usually with a red-shifted shoulder, attributed to polymethine dyes (Table 3 and Supporting Information, Figures S17, S20, S24, S25, S28, and S31). The presence of a shoulder in the luminescence spectrum is characteristic for polymethine dyes and usually associated with their aggregation. The fluorescence spectrum of CPFPM2 in chloroform contains a band at 557 nm associated with benzothiadiazole fragments, in addition to bands attributed to fluorene and polymethine units (Table 3 and Supporting Information, Figure S20).\u003c/p\u003e\n\u003cp\u003eThe fluorescence spectra of CPFPMs in the film have a more intense band of the polymethine dye relative to the emission bands of polyfluorene compared to the spectra in a chloroform solution, which is caused by a more efficient energy transfer from polyfluorene to the polymethine fragment due to aggregation in the solid phase (Figs. 3, 4 and Supporting Information, Figures S18, S21, S26, S29, and S32).\u003c/p\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003ePhotophysical characteristics of CPFPMs (λ\u003csub\u003eex\u003c/sub\u003e = 385 nm)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003ePolymer\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eλ\u003csub\u003eabs\u003c/sub\u003e, nm\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eλ\u003csub\u003eem\u003c/sub\u003e, nm\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eλ\u003csub\u003eabs\u003c/sub\u003e, nm\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eλ\u003csub\u003eem\u003c/sub\u003e, nm\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003echloroform solution\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003efilm\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e388, 680\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e418, 440, 471*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e430, 455, 485*, 710\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385, 440*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e417, 440, 471*, 557, 620*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e387, 424*, 465*, 601\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e418*, 436, 532, 682*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e390, 437, 474, 555, 757\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e417, 440, 471\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e385\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e433, 460, 492, 533\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e389, 670\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e417, 440, 471*, 683\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e383, 625*, 680\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e434, 460, 489, 693, 747*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCPFPM5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e386, 625*, 670\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e417, 440, 471*, 691, 746*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e379, 628*, 679\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e416, 437, 469*, 705\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e* Shoulder\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eThe influence of acid and base additives on the photophysical properties of CPFPMs\u003c/p\u003e\n\u003cp\u003eThe effect of pH on the absorption and emission spectra of CPFPMs in a chloroform solution was studied. We have compared the spectra of CPFPMs in pure chloroform and in the presence of trifluoroacetic acid (TFA, 0.022 M) and triethylamine (TEA, 0.24 M) in chloroform solutions (Supporting Information, Figures S15−S17, S19, S20, S22−S25, S27, S28, S30, and S31).\u003c/p\u003e\n\u003cp\u003eThe addition of TFA and TEA to the CPFPM1 solution has practically no effect on the UV absorption and luminescence spectra (Supporting Information, Figures S15−S17). Also, no changes were observed in the UV-Vis absorption spectrum of the CPFPM2 solution upon the addition of acid and base (Supporting Information, Figure S19). However, in the luminescence spectrum of CPFPM2 (Fig. 4), the intensity of the band of 2,1,3-benzothiadiazole at 557 nm decreases with the addition of acid (Supporting Information, Figures S20 and S33). Interestingly, the acid doesn’t influence luminescence of 2,1,3-benzothiadiazole solution, but strongly affects the photophysical properties of CPFPM2.\u003c/p\u003e\n\u003cp\u003eA good fit linear relation between the integral fluorescence intensity of the long-wavelength band and the logarithm of the TFA concentration was observed (Supporting Information, Figure S33).\u003c/p\u003e\n\u003cp\u003eFor an acidic solution of CPFPM3, the absorption band of the dye is blue-shifted from 757 to 563 nm (Supporting Information, Figure S23). Due to the absorption of fluorene in the region of 380−450 nm, the solution in an acidic medium is colored blue-violet. The long-wavelength band in the UV-Vis absorption spectrum of CPFPM3 in a chloroform solution with the addition of TEA is located at 550 nm.\u003c/p\u003e\n\u003cp\u003eThe luminescence spectrum of the acidic solution of CPFPM3 shows a band at 750 nm, while the addition of TEA results in the appearance of a band at 618 nm (Supporting Information, Figure S25).\u003c/p\u003e\n\u003cp\u003eSince polymers CPFPM4 and CPFPM5 have a similar nature and differ only in the content of squaraine dye, the UV-Vis and luminescence spectra of their solutions in chloroform have the same bands, but the squaraine dye bands have higher intensities in the spectra of CPFPM5 (Supporting Information, Figures S27, S28, S30, and S31).\u003c/p\u003e\n\u003cp\u003eThe influence of acid and base additives on the UV-Vis and luminescence spectra was studied for CPFPM5 in chloroform solution (Supporting Information, Figures S28 and S31). The addition of TEA does not lead to significant changes in the absorption and emission spectra of CPFPM5. However, the intensity of the absorption and emission bands of the squaraine dye (670 and 691 nm, respectively) decreases upon the addition of TFA (Fig. 5 and Supporting Information, Figures S34−S36).\u003c/p\u003e\n\u003cp\u003eThe graph of the dependence of fluorescence intensity on the logarithm of the concentration of trifluoroacetic acid has two linear regions with different slopes (Supporting Information, Figure S35). This is due to the possibility of protonation of two oxygen atoms of the squaraine ring.\u003c/p\u003e\n\u003cp\u003eThus, copolyfluorenes with ketocyanine and squaraine units are promising materials for pH determination, especially in acidic media. Aggregation of molecules leads to a significant enhancement of the polymethine dye band in the emission spectra.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we have synthesized a series of copolyfluorenes containing polymethine dyes with absorption and emission from violet to red region. Their photophysical properties were studied both in solution and in the solid state. A hyperchromic effect is observed for the emission band of the polymethine unit of CPFPMs in the film compared to the chloroform solution, which is due to the aggregation induced emission. The influence of acid (TFA) and base (TEA) on UV-Vis absorption and emission spectra was also considered. The absorption and fluorescence spectra of CPFPM3 show changes in the presence of both TFA and TEA. For CPFPM2, CPFPM4 and CPFPM5, the intensity of the polymethine dye band in the emission spectra was most clearly reduced by the addition of TFA. The acidity has the greatest effect on the fluorescence spectrum of CPFPM5.\u003c/p\u003e\u003cp\u003eThe incorporation of polymethine dyes, especially ketocyanine and squaraine into polymers has provided opportunities for rapid and efficient pH determination in non-aqueous media. On the other hand, the presence of fluorene in the polymer chain leads to an increase in the fluorescence intensity of polymethine units in the red and NIR regions, which is most strongly manifested in the aggregated state. Thus, the synthesis and study of the properties of copolymers based on polymethine dyes is of considerable interest for the development of new luminescent materials, Pdots, and chemosensors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe work was funded by the National Research Center \u0026ldquo;Kurchatov Institute\u0026rdquo; under the state assignment № 1023031700043-2-1.4.4.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e Elena V. Zhukova: Investigation (lead). Alexander M. Mitroshin: Investigation (supporting). Ksenia I. Kaskevich: Investigation (supporting). Serguei A. Miltsov: Investigation (lead); formal analysis (lead). Larisa S. Litvinova: Investigation (supporting). Tatiana G. Chulkova: Data curation (supporting); formal analysis (lead); writing \u0026ndash; original draft (lead). Alexander V. Yakimansky: Data curation (lead); formal analysis (lead); resources (lead); supervision (lead); writing \u0026ndash; review and editing (lead).\u0026nbsp;\u003c/p\u003e \n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e The National Research Center \u0026ldquo;Kurchatov Institute\u0026rdquo;, state assignment № 1023031700043-2-1.4.4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Data sharing does not apply to this article as no datasets were generated or analyzed during the current study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003eThe authors declare no conficts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eOu YF, Ren TB, Yuan L, Zhang XB (2023) Molecular Design of NIR-II Polymethine Fluorophores for Bioimaging and Biosensing. Chem Biomed Imaging 1:220\u0026ndash;233. https://doi.org/10.1021/cbmi.3c00040\u003c/li\u003e\n\u003cli\u003eGastaldi M, Cardano F, Zanetti M, et al (2021) Functional Dyes in Polymeric 3D Printing: Applications and Perspectives. ACS Mater Lett 3:1\u0026ndash;17. https://doi.org/10.1021/acsmaterialslett.0c00455\u003c/li\u003e\n\u003cli\u003eIlina K, MacCuaig WM, Laramie M, et al (2020) Squaraine Dyes: Molecular Design for Different Applications and Remaining Challenges. Bioconjug Chem 31:194\u0026ndash;213. https://doi.org/10.1021/acs.bioconjchem.9b00482\u003c/li\u003e\n\u003cli\u003eShindy HA (2017) Fundamentals in the chemistry of cyanine dyes: A review. Dye Pigment 145:505\u0026ndash;513. https://doi.org/10.1016/j.dyepig.2017.06.029\u003c/li\u003e\n\u003cli\u003eBifari EN, Almeida P, El-Shishtawy RM (2023) Advancing panchromatic effect for efficient sensitization of cyanine and hemicyanine-based dye-sensitized solar cells. Mater Today Energy 36:101337. https://doi.org/10.1016/j.mtener.2023.101337\u003c/li\u003e\n\u003cli\u003eSun W, Guo S, Hu C, et al (2016) Recent Development of Chemosensors Based on Cyanine Platforms. Chem Rev 116:7768\u0026ndash;7817. https://doi.org/10.1021/acs.chemrev.6b00001\u003c/li\u003e\n\u003cli\u003eKelderhouse LE, Chelvam V, Wayua C, et al (2013) Development of Tumor-Targeted Near Infrared Probes for Fluorescence Guided Surgery. Bioconjug Chem 24:1075\u0026ndash;1080. https://doi.org/10.1021/bc400131a\u003c/li\u003e\n\u003cli\u003eZhang H, Yan C, Li H, et al (2021) Rational Design of Near-Infrared Cyanine-Based Fluorescent Probes for Rapid In Vivo Sensing Cysteine. ACS Appl Bio Mater 4:2001\u0026ndash;2008. https://doi.org/10.1021/acsabm.0c00260\u003c/li\u003e\n\u003cli\u003eGamage RS, Li D-H, Schreiber CL, Smith BD (2021) Comparison of cRGDfK Peptide Probes with Appended Shielded Heptamethine Cyanine Dye ( s775z ) for Near Infrared Fluorescence Imaging of Cancer. ACS Omega 6:30130\u0026ndash;30139. https://doi.org/10.1021/acsomega.1c04991\u003c/li\u003e\n\u003cli\u003eYang Z, Sun Q, Ji L, et al (2025) Recent Advances for Synthesis and Bioapplications of Polymethine Cyanines. Asian J Org Chem. https://doi.org/10.1002/ajoc.202500109\u003c/li\u003e\n\u003cli\u003eLiu Q, Ding X, Xu X, et al (2022) Tumor-targeted hyaluronic acid-based oxidative stress nanoamplifier with ROS generation and GSH depletion for antitumor therapy. Int J Biol Macromol 207:771\u0026ndash;783. https://doi.org/10.1016/j.ijbiomac.2022.03.139\u003c/li\u003e\n\u003cli\u003eYang Z-C, Gu Q-S, Chao J-J, et al (2024) Glutathione-activated biotin-targeted dual-modal imaging probe with improved PDT/PTT synergistic therapy. Anal Chim Acta 1316:342860. https://doi.org/10.1016/j.aca.2024.342860\u003c/li\u003e\n\u003cli\u003eXu Y, Meng X, Zhao Y, et al (2024) Pyrrolopyrrole Cyanine J-Aggregate Nanoparticles with High Near-Infrared Fluorescence Brightness and Photothermal Performance for Efficient Phototheranostics. ACS Appl Mater Interfaces 16:39005\u0026ndash;39020. https://doi.org/10.1021/acsami.4c06225\u003c/li\u003e\n\u003cli\u003eCao C, Zhou X, Xue M, et al (2019) Dual Near-Infrared-Emissive Luminescent Nanoprobes for Ratiometric Luminescent Monitoring of ClO \u0026ndash; in Living Organisms. ACS Appl Mater Interfaces 11:15298\u0026ndash;15305. https://doi.org/10.1021/acsami.9b02008\u003c/li\u003e\n\u003cli\u003eWang R, Han X, You J, et al (2018) Ratiometric Near-Infrared Fluorescent Probe for Synergistic Detection of Monoamine Oxidase B and Its Contribution to Oxidative Stress in Cell and Mice Aging Models. Anal Chem 90:4054\u0026ndash;4061. https://doi.org/10.1021/acs.analchem.7b05297\u003c/li\u003e\n\u003cli\u003eShahane SD, Mudliar NH, Chawda BR, et al (2025) YOPRO-1: A Cyanine-Based Molecular Rotor Probe for Amyloid Fibril Detection. ACS Appl Bio Mater 8:3443\u0026ndash;3453. https://doi.org/10.1021/acsabm.5c00186\u003c/li\u003e\n\u003cli\u003eLi Y, Chen C, Xu D, et al (2018) Effective Theranostic Cyanine for Imaging of Amyloid Species in Vivo and Cognitive Improvements in Mouse Model. ACS Omega 3:6812\u0026ndash;6819. https://doi.org/10.1021/acsomega.8b00475\u003c/li\u003e\n\u003cli\u003eBai L, Jia Y, Wang Z, et al (2025) Albumin Encapsulation of Cyanine Dye for High-Performance NIR-II Imaging-Guided Photodynamic Therapy. Chem Biomed Imaging. https://doi.org/10.1021/cbmi.5c00005\u003c/li\u003e\n\u003cli\u003eJiang S, Li W, Li B, et al (2025) Albumin-Energized NIR-II Cyanine Dye for Fluorescence/Photoacoustic/Photothermal Multi-Modality Imaging-Guided Tumor Homologous Targeting Photothermal Therapy. J Med Chem 68:3324\u0026ndash;3334. https://doi.org/10.1021/acs.jmedchem.4c02369\u003c/li\u003e\n\u003cli\u003eSun H, Sun R, Yang D, et al (2024) A Cyanine Dye for Highly Specific Recognition of Parallel G-Quadruplex Topology and Its Application in Clinical RNA Detection for Cancer Diagnosis. J Am Chem Soc 146:22736\u0026ndash;22746. https://doi.org/10.1021/jacs.4c07698\u003c/li\u003e\n\u003cli\u003eNano A, Boynton AN, Barton JK (2017) A Rhodium-Cyanine Fluorescent Probe: Detection and Signaling of Mismatches in DNA. J Am Chem Soc 139:17301\u0026ndash;17304. https://doi.org/10.1021/jacs.7b10639\u003c/li\u003e\n\u003cli\u003eSaarnio VK, Salorinne K, Ruokolainen VP, et al (2020) Development of functionalized SYBR green II related cyanine dyes for viral RNA detection. Dye Pigment 177:108282. https://doi.org/10.1016/j.dyepig.2020.108282\u003c/li\u003e\n\u003cli\u003ePontremoli C, Chinig\u0026ograve; G, Galliano S, et al (2023) Photosensitizers for photodynamic therapy: Structure-activity analysis of cyanine dyes through design of experiments. Dye Pigment 210:111047. https://doi.org/10.1016/j.dyepig.2022.111047\u003c/li\u003e\n\u003cli\u003eRozovsky A, Patsenker L, Gellerman G (2019) Bifunctional reactive pentamethine cyanine dyes for biomedical applications. Dye Pigment 162:18\u0026ndash;25. https://doi.org/10.1016/j.dyepig.2018.09.064\u003c/li\u003e\n\u003cli\u003eChen L, Wu L, Yu J, et al (2017) Highly photostable wide-dynamic-range pH sensitive semiconducting polymer dots enabled by dendronizing the near-IR emitters. Chem Sci 8:7236\u0026ndash;7245. https://doi.org/10.1039/C7SC03448B\u003c/li\u003e\n\u003cli\u003eVerma M, Chan Y-H, Saha S, Liu M-H (2021) Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging. ACS Appl Bio Mater 4:2142\u0026ndash;2159. https://doi.org/10.1021/acsabm.0c01185\u003c/li\u003e\n\u003cli\u003eChen Y-H, Kuo S-Y, Tsai W-K, et al (2016) Dual Colorimetric and Fluorescent Imaging of Latent Fingerprints on Both Porous and Nonporous Surfaces with Near-Infrared Fluorescent Semiconducting Polymer Dots. Anal Chem 88:11616\u0026ndash;11623. https://doi.org/10.1021/acs.analchem.6b03178\u003c/li\u003e\n\u003cli\u003eWu I-C, Yu J, Ye F, et al (2015) Squaraine-Based Polymer Dots with Narrow, Bright Near-Infrared Fluorescence for Biological Applications. J Am Chem Soc 137:173\u0026ndash;178. https://doi.org/10.1021/ja5123045\u003c/li\u003e\n\u003cli\u003eLi X, Chen H, Su Z, et al (2024) Brightness Strategies toward NIR-II Emissive Conjugated Materials: Molecular Design, Application, and Future Prospects. ACS Appl Bio Mater 7:8019\u0026ndash;8039. https://doi.org/10.1021/acsabm.4c00137\u003c/li\u003e\n\u003cli\u003eLawrance R, Chowdhury P, Lin H-C, Chan Y-H (2024) The luminous frontier: transformative NIR-IIa fluorescent polymer dots for deep-tissue imaging. RSC Appl Polym 2:749\u0026ndash;774. https://doi.org/10.1039/D4LP00076E\u003c/li\u003e\n\u003cli\u003eReddington M V. (2007) Synthesis and Properties of Phosphonic Acid Containing Cyanine and Squaraine Dyes for Use as Fluorescent Labels. Bioconjug Chem 18:2178\u0026ndash;2190. https://doi.org/10.1021/bc070090y\u003c/li\u003e\n\u003cli\u003eLloyd D, McNab H, Marshall DR (1973) Diazepines; XVII 1 . Simple Preparation of 2,3-Dihydro-1 H -1,4-diazepinium Perchlorate. Synthesis (Stuttg) 1973:791\u0026ndash;791. https://doi.org/10.1055/s-1973-22305\u003c/li\u003e\n\u003cli\u003eLindsey JS, Brown PA, Siesel DA (1989) Visible light-harvesting in covalently-linked porphyrin-cyanine dyes. Tetrahedron 45:4845\u0026ndash;4866. https://doi.org/10.1016/S0040-4020(01)85156-5\u003c/li\u003e\n\u003cli\u003eMiltsov S, Goikhman M, Yakimansky A, et al (2019) N-Bromosuccinimide-mediated dimerization of unsymmetrical indodicarbocyanine dyes. Tetrahedron Lett 60:151005. https://doi.org/10.1016/j.tetlet.2019.151005\u003c/li\u003e\n\u003cli\u003eSlominskii YL, Radchenko ID, Popov S V., Tolmachev AI (1983) Polymethine dyes with hydrocarbon bridges. Enamine ketones in the chemistry of cyanine dyes. Zh Org Khim 19:2134\u0026ndash;2142\u003c/li\u003e\n\u003cli\u003eSmyslov RY, Tomilin FN, Shchugoreva IA, et al (2019) Synthesis and photophysical properties of copolyfluorenes for light-emitting applications: Spectroscopic experimental study and theoretical DFT consideration. Polymer (Guildf) 168:185\u0026ndash;198. https://doi.org/10.1016/j.polymer.2019.02.015\u003c/li\u003e\n\u003cli\u003eYevlampieva NP, Khurchak AP, Nosova GI, et al (2016) Chain microstructure and specific features of excitation energy transfer in solution and films of poly(9,9-dioctylfluorene) doped with 2,1,3-benzothiadiazole comonomer units. Chem Phys Lett 645:100\u0026ndash;105. https://doi.org/10.1016/j.cplett.2015.12.039\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Copolyfluorenes, Cyanine dyes, Fluorescence, pH-sensitivity, Polymethine dyes, Squaraine dyes","lastPublishedDoi":"10.21203/rs.3.rs-6732791/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6732791/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDespite the huge progress in the synthesis of small organic fluorophores and inorganic materials emitting in the red and near-infrared region, the synthesis of π-conjugated polymers with fluorescence in this range remains a challenging task. A series of fluorene-polymethine dye copolymers were synthesized by the Suzuki-Miyaura coupling polycondensation using cyanine, keto-cyanine, and squaraine comonomers, which exhibit fluorescence at \u003cem\u003eca.\u003c/em\u003e 500\u0026minus;700 nm. These polymers exhibit both green to red or near-infrared absorption and emission attributed to polymethine dyes, and absorption and emission bands corresponding to polyfluorene (at \u003cem\u003eca.\u003c/em\u003e 380 and 420\u0026minus;470 nm, respectively). The influence of pH on the UV-Vis absorption and luminescence spectra of the copolymers in solution was studied.\u003c/p\u003e","manuscriptTitle":"Copolyfluorenes containing polymethine dyes in the main chain: synthesis and photophysical properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-11 18:03:46","doi":"10.21203/rs.3.rs-6732791/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-07-09T08:12:29+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-09T07:32:08+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2025-06-18T18:03:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-29T08:58:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2025-05-28T05:36:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"920356bf-6040-41a4-aa91-b2fed7c22bf5","owner":[],"postedDate":"July 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-13T16:07:03+00:00","versionOfRecord":{"articleIdentity":"rs-6732791","link":"https://doi.org/10.1007/s10965-025-04608-5","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2025-10-09 15:57:58","publishedOnDateReadable":"October 9th, 2025"},"versionCreatedAt":"2025-07-11 18:03:46","video":"","vorDoi":"10.1007/s10965-025-04608-5","vorDoiUrl":"https://doi.org/10.1007/s10965-025-04608-5","workflowStages":[]},"version":"v1","identity":"rs-6732791","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6732791","identity":"rs-6732791","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}