Donor-Acceptor Intermediates and Low-Bandgap Polymers by Electropolymerization of Thienoazaborines

New low-bandgap polythiophenes (E-g similar to 1.2 eV) with thienoquinodiimine and diphenylbithiophene alternating moieties were synthesized via electrochemical polymerization of azaborines 1a and 1b. The polymers were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), vis-NIR spectroelectrochemistry, and X-ray photoelectron spectroscopy (XPS). Formation of these polymers is accompanied by boron expulsion from the fused dithienoazaborine system and formation of a new C C bonds between thiophene backbone and phenyl substituents. This finding was supported by isolating the intermediates 2 and 3 with partially deborylated structures. The optoelectronic properties of the later, investigated by UV-vis spectroscopy and CV, are controlled by the interaction between the donor (amino-substituted thiophene) and acceptor (thienoazaborine) moieties which is weak in the ground state due to twisted structure of the molecule but is enhanced in the excited state leading to large fluorescence Stokes shift.