Connector effect in electroluminescent properties of poly(p-phenylene vinylene) derivatives containing triazole chromophores

We report the thermal, optical, electrochemical and electroluminescent properties of four polymers P1-P4 consisting of hole-transporting [1,4-bis(hexyloxy)-2,5-distyrylbenzene;DSB] and electron-transporting [4-(4-(hexyloxy)phenyl)-3,5-diphenyl-4H-1,2,4-triazole; TAZ] fluorophores linked by four kinds of connectors: (1) ether spacers, (2) single bonds, (3) 1,4-phenylenes, and (4) 1,4-divinylbenzenes. These polymers are soluble in common organic solvents such as chloroform, N-methylpyrrolidone (NMP) and CH2Cl2CH2Cl2 and exhibit good thermal stability with decomposition temperatures higher than 340 degrees C. Compounds M1-M3 containing a TAZ or DSB core were employed as a model to study the optical properties of the polymers. The photoluminescence (PL) spectral maxima of P1-P4 in CHCl3 were spread over a wide range, from 453 nm to 501 nm, depending upon the chemical structures of the connectors. In the film state, the PL maxima shifted bathochromically from 464 nm to 538 nm, which can be attributed to the formation of excimers. From the optimized semiempirical modified neglect of diatomic overlap (MNDO) calculations, the adjacent benzene rings between DSB and TAZ chromophores in P2 and P3 twist about 81-89' which is significantly different from P4 (circa 0 degrees). The effect of the twisted connector architectures on optical and electrochemical properties for P1-P4 is discussed.