Synthesis and optically acid-sensory and electrochemical properties of novel polyoxadiazole derivatives

A series of PPV-based polyoxadiazoles have been synthesized by Horner and Suzuki coupling polymerization to investigate their structure-property relationship. These copolymers exhibit good thermal stability (decomposition temperature around 352-413°C). Excimer formation in P4-P9 was confirmed by their absorption and PL spectral peak transition in solution at different concentrations and in thin films. Unusual absorption and fluorescence were observed in acid media and have been related to photoinduced charge transfer in alternating donor-acceptor architecture. The photoinduced charge transfer led to a blue shift in iminodibenzyl-containing copolymers (P1-P3) and a red shift in fluorene-containing copolymers (P9), reflecting the fact that iminodibenzyl is a stronger electron-donating unit. The electrochemical properties of the copolymers were evaluated by cyclic voltammetry and their highest occupied molecular orbital and the lowest unoccupied molecular orbit energy levels were estimated. The optical band gaps of the dioxadiazole-containing copolymers show great discrepancy with the electrochemical band gap energy due to the donor-acceptor feature of the dioxadiazole unit.