Structure-property relationships of fluorinated donor/acceptor tetrakis(phenylethynyl)benzenes and bis(dehydrobenzoannuleno)benzenes

Nine new bisdonor/bisacceptor-functionalized tetrakis(phenylethynyl)benzene (TPEB) and six new bis(dehydrobenzoannuleno)benzene (DBA) chromophores have been synthesized. The compounds consist of electron-donating dibutylaniline groups connected through a conjugated phenyl -acetylene scaffold to benzotrifluoride, bis(trifluoromethyl)phenyl, or pentafluorophenyl acceptor groups. In comparison to previously reported analogues utilizing nitrophenyl or benzonitrile acceptor groups, the weaker acceptor groups exhibit visibly fluorescent intramolecular charge transfer (ICT) behavior, moderately narrow optical band gaps, moderately high quantum yields, and strong fluorescence solvatochromism. In this series of molecules, the strongly inductive fluoro acceptor groups result in optical properties similar to the resonance acceptor analogues, making them promising candidates for optical materials device components. The data also support recent investigations that question the utility of using UV/vis spectroscopy alone as a qualitative measure of conjugation. The bisDBAs exhibit weaker ICT behavior and self-association in solution than their corresponding nitro analogues, but show greater stability to decomposition via polymerization and smaller optical band gaps than their acyclic analogues.