The effect of alkyl chain lengths on the red-to-near-infrared emission of boron-fused azomethine conjugated polymers and their film-state stimuli-responsivities

We present systematic studies of the dependencies of the red-to-near-infrared emission and stimuli-responsive properties of boron-fused azomethine ( BAm ) conjugated copolymers on the lengths of their alkyl side chains. We prepared a series of bithiophene copolymers with variable alkyl side chain lengths on the BAm and bithiophene moieties and evaluated their optical properties in solution and their stimuli-responsivity in films before and after vapor annealing. In the UV-vis absorption and emission spectra, it was shown that the elimination of the alkyl side chains on the bithiophene ( BT ) units led to a remarkable red-shift relative to that of the original polymer in the emission spectra. Theoretical calculations revealed that the enhancement of the planarity between the two thiophene rings played a significant role in the spectral red-shifting. Finally, a drastic red-shift in the emission ( ca. 40 nm) was observed upon vapor annealing without a loss of emission efficiency ( Φ F = 0.36). We present systematic studies of the dependence of the red-to-near-infrared emission and stimuli-responsive properties of boron-fused azomethine conjugated copolymers on the lengths of the alkyl chains.