Boron Difluoride Formazanate Copolymers with 9,9-Di-n-hexylfluorene Prepared by Copper-Catalyzed Alkyne-Azide Cycloaddition Chemistry
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The synthesis and characterization of copolymers based on boron difluoride formazanate (BF2L) and 9,9-di-n-hexylfluorene (hex2Fl) units are described. A series of model compounds [(BF2L)-(hex2Fl), (hex2Fl)-(BF2L)-(hex2Fl), and (BF2L)-(hex2Fl)-(BF2L)] were also studied in order to fully understand the spectroscopic properties of the title copolymer [(BF2L)-(hex2Fl)]n. The model compounds and copolymers, which were synthesized by copper catalyzed alkyne-azide cycloaddition chemistry, exhibited high molar absorptivities (25,700-54,900 M-1 cm-1), large Stokes shifts (123-143 nm, 3590-3880 cm-1), and tunable electrochemical behaviour (E°red1 ca. -0.75 V and E°red2 ca. -1.86 V vs. ferrocene/ferrocenium). The low-energy wavelength of maximum absorption and emission of the model compounds red-shifted relative to the BF2L repeating unit by ca. 30 nm per triazole ring formed, to maximum values of 557 nm and 700 nm in DMF, respectively. The low-energy absorption and emission properties of the copolymer were consistent with the model compound bearing two triazole rings [(hex2Fl)-(BF2L)-(hex2Fl)] and were not dependant on copolymer molecular weight. However, the title copolymers may show promise as a light-harvesting material based on their thin-film optical band gap of 1.67 eV.