Vinyl copolymers containing pendant 1,4-distyrylbenzene and 1,3,4-oxadiazole chromophores: Preparation and optoelectronic properties

We prepared two vinyl copolymers P1 and P2 containing pendant distyrylbenzene and aromatic 1,3,4-oxadiazole derivatives, respectively, from their precursor poly(styrene-ran-4-vinylbenzyl chloride) (M_w = 11,400, PDI = 1.18), which had been prepared by the controlled radical polymerization (RAFT). Two main chain polymers containing similar isolated distyrylbenzene (P3) and aromatic 1,3,4-oxadiazole (P4) chromophores were also synthesized for comparative study. The resulted copolymers (P1-P4) are soluble in common organic solvents and are basically amorphous materials with 5% weight-loss temperature higher than 360°C. The PL spectral results reveal that the architecture of PI prevents the formation of inter- or intramolecular interaction. The HOMO and LUMO levels of P2, estimated from cyclic voltammetric data, are -5.96 and -3.81 eV, respectively, which are much lower than those of PI (-5.12 and -3.11 eV). The emission of blend from PI and P2 are contributed mainly from distyrylbenzene fluorophore (∼450 nm) owing to efficient energy transfer. Moreover, the blend exhibits three kinds of redox behavior depending on their weight ratios. The luminance and current efficiency of the EL device (ITO/ PEDOT/MEH-PPV+P2/A1) are 503 cd/m² and 0.11 cd/A, which can be improved to 1285 cd/m² and 0.44 cd/A, respectively, as the weight ratio of P2 increases from 0 to 20%.