Synthesis, photophysics, and electroluminescence of conjugated poly(p-phenylenevinylene) derivatives with 1,3,4-oxadiazoles in the backbone

Starting from 4-bromobenzaldehyde or 1,4-benzenedicarboxaldehyde, two new poly(p-phenylenevinylene) derivatives P1 and P2 were synthesized by a five-step synthetic route. These fully conjugated polymers contain 1 or 2 oxadiazole rings and 3 or 4 vinylene bonds per repeat unit for P1 and P2, respectively, and were amorphous and soluble in common organic solvents. The T, values were 28 degreesC for P1 and 57 degreesC for P2. The polymers emitted greenish-blue light in solution with photoluminescence (PL) emission maximum at 487-511 nm and yellowish-green light with PL emission maximum at 515558 nm in thin films. Electroluminescence (EL) was achieved from single-layer LEDs of polymer P1 with the configuration ITO/PEDOT/P1/Al with voltage-tunable EL colors from 558 nm (9 V) to 527 nm (16 V). The observed EL spectral blue shift with increasing voltage is a result of conformational changes of the polymer backbone with increase in temperature, as evidenced from the absorption and PL spectra changes upon annealing of P1 thin films at different temperatures.