文摘
Torsionally responsive molecular systems can change their electronic properties according to the dihedral angles and can be utilized as sensory materials. We have designed and synthesized novel tropone-fused conjugated polymers PBTr, PBTr-T, and PBTr-Tz that showed interesting dihedral-angle-dependent variations in UV鈥搗is absorptions. Tropone-fused thiophene derivatives were prepared from one-step condensation of thiophene-3,4-dialdehyde and aliphatic ketones via a modular, facile, and high-yielding method. Subsequent halogenation and Stille cross-coupling polymerization with a bis(stannyl)benzodithiophene resulted in a tropone-fused conjugated polymer PBTr. We were also able to prepare thiophene- and thiazole-bridged polymers, PBTr-T and PBTr-Tz, respectively, using similar synthetic methods. Electronic absorptions of the newly synthesized PBTrs were measured in solutions and in films states. Substantial red-shifts occurred in the case of thiophene-bridged PBTr-T, whereas almost no shift was observed for thiazole-bridged PBTr-Tz. We attributed this to the substantial change in the torsional angle between the tropone-fused thiophene moiety and thiophene, which was further supported by density functional theory (DFT) calculations. Similar spectral changes of UV鈥搗is absorptions were observed when a poor solvent (methanol) was introduced to a chloroform solution of PBTr-T. Reverse torsional angle variations were realized with initially planar PBTr-Tz by introducing steric hindrance through protonation on the thiazole rings. We believe that torsionally responsive tropone-fused conjugated polymers are promising as novel platforms for sensory applications.
