苯/二联苯为桥的噻吩-吡咯-噻吩结构:分子构型及电致变色性质

摘要

合成了两种以苯或二联苯为桥键单元的噻吩-吡咯-噻吩衍生物(PhSNS、BPhSNS),并通过电化学聚合形成具有交联结构的聚合物薄膜(pPhSNS、pBPhSNS).两种单体的循环伏安曲线表明,相比BPhSNS的一个氧化峰,PhSNS表现出两个氧化峰,理论计算结果表明这可能主要是由于PhSNS化合物中的两条噻吩-吡咯-噻吩具有不同的分子构型,其中一条噻吩-吡咯-噻吩中噻吩与吡咯单元的扭曲角为21.2°,另一条噻吩-吡咯-噻吩中噻吩与吡咯单元的扭曲角为40.2°,这使得PhSNS的HOMO-1和HOMO表现出比较大的能隙(～0.4 eV),因而导致出现两个峰;BPhSNS结构中两条噻吩-吡咯-噻吩的分子构型相同,使得HOMO-1和HOMO很相似,因此其电化学只出现一个峰.然而,两个单体表现出相同的起始氧化还原电位,同时相应的聚合物表现出相似的氧化还原曲线,使得两种聚合物薄膜表现出相似的电致变色性质.光谱电化学表明,pPhSNS和pBPhSNS表现出相似的光学吸收及相似的颜色变化(黄色-灰绿色-灰色);此外,pPhSNS和pBPhSNS表现出快速的响应速度(1100 nm处分别为0.57和0.93 s),同时表现出合理的光学对比度(1100 nm处分别为46％和31％);这些研究将为关联分子构型与单体的电化学、聚合物的电致变色性质三者之间的关系提供一定的借鉴与帮助.%A series of multi-branched dithienylpyrrole (SNS) monomers with rigid phenyl (PhSNS) and biphenyl rings (BPhSNS) as bridges were designed and synthesized,and were fabricated to form cross-linked polymers (pPhSNS,pBPhSNS) by electrochemical polymerization.Cyclic voltammetry (CV) results showed that PhSNS and BPhSNS exhibited similar oxidative properties except for one new higher-potential oxidative peak appearing in the curves of PhSNS.Theoretical calculations indicated that it should be attributed to the different steric configuration between the two dithienylpyrrole (SNS) units in PhSNS.One SNS unit possessed a larger twist angle (40.2°) between thiophene and pyrrole rings than the other one (21.2°),which indicated that PhSNS possessed a relatively larger energy gap (～0.4 eV) between HOMO-1 and HOMO than BPhSNS,for which HOMO and HOMO-1 levels were of almost the same energy.However,both PhSNS and BPhSNS showed similar onset oxidation potentials.The CV curves of pPhSNS and pBPhSNS showed that they presented similar oxidative properties,which enabled their corresponding electrochemical polymers to exhibit similar electrochromic properties.The UV-vis spectra of the corresponding polymers showed that both pPhSNS and pBPhSNS possessed similar optical absorption and similar multicolor switching between yellow (-0.8 V),greyish-green (0.9 V) and gray (1.1 V) colors.Besides,pPhSNS and pBPhSNS showed fast switching times of 0.57 s and 0.93 s at 1100 nm,respectively and reasonable contrasts of 46％ and 31％ at 1100 nm,respectively.These investigations may help understand the relationship between structural configuration and the electrochemistry/electrochromic properties for polymer electrochromic (PEC) materials research.