A Cyano-Substituted Organoboron Electron-deficient Building Block for D-A Type Conjugated Polymers

The development of donor-acceptor(D-A) type conjugated polymers depends largely on the design of novel A building blocks.Herein, we report a novel A building block based on the cyano-substituted organoboron unit(SBN-3). Compared with the most common fluorine-substituted B←N unit, SBN-3 displays a significantly downshifted LUMO energy level because of the strong electron-withdrawing ability of cyano groups. In addition, due to the greater impact of cyano substitution on LUMO than on HOMO, SBN-3 exhibits a reduced band gap, nearinfrared absorption and fluorescence properties. The D-A type conjugated polymers based on the cyano-substituted B←N unit with thiophene-based units show narrow optical band gaps of ca. 1.3 e V as well as distinctive electronic structures, i.e., delocalized LUMOs and localized HOMOs.This work thus provides not only an effective approach to design strong A units but also a new electron-deficient building block for D-A type conjugated polymers.