Boron difluoride formazanate copolymers with 9,9-di-n-hexylfluorene prepared by copper-catalyzed alkyne-azide cycloaddition chemistry

The synthesis and characterization of copolymers based on boron difluoride formazanate (BF2L) and 9,9-di-n-hexylfluorene (hex(2)Fl) units are described. A series of model compounds [(BF2L)-(hex(2)Fl), (hex(2)Fl)-(BF2L)-(hex(2)Fl), and (BF2L)-(hex(2)Fl)-(BF2L)] were also studied in order to fully understand the spectroscopic properties of the title copolymers [(BF2L)-(hex(2)Fl)](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 degrees ca. -0.75 V and E-red2 degrees 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 [(hex(2)Fl)-(BF2L)-(hex(2)Fl)] and were not dependent on copolymer molecular weight. However, the title copolymers may show promise as light-harvesting materials based on their thin-film optical band gap of 1.67 eV.