Vinyl copolymers containing pendant 1,4-distyryl benzene 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 degrees C. The PL spectral results reveal that the architecture of P1 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 P1 (-5.12 and -3.11 eV). The emission of blend from P1 and P2 are contributed mainly from distyrylbenzene fluorophore (similar to 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/Al) are 503 cd/m(2) and 0.11 cd/A, which can be improved to 1285 cd/m(2) and 0.44 cd/A, respectively, as the weight ratio of P2 increases from 0 to 20%. (c) 2006 Wiley Periodicals, Inc.