A new class of organosoluble rigid-rod, fully aromatic poly(1,3,4-oxadiazole)s and their solid-state properties, 2 - solid-state Properties

Full Paper: New symmetrical and unsymmetrical dialkoxy-substituted aromatic poly(1,3,4-oxadiazole)s are investigated by cyclovoltammetric measurements. The electrochemical redox behaviour of these materials is compared with the chemical structure. The reduction behaviour allows the estimation of the electron affinity, and shows that these polymers are suitable candidates for electron-transport materials in electronic devices. Surprisingly it is found from UV-vis and fluorescence spectroscopic measurements that the polyoxadiazole with linear alkoxy side chains (C16) shows a reversible thermochromism in solution as well as in the solid state. The changes in this temperature range are ascribed to a phase transition between aggregated chains, in solution as well as in the film, at room temperature and molecularly dissolved polymer chains at higher temperature. The other poly(1,3,4-oxadiazole)s with branched alkoxy side chains exhibit an improved solubility and they are completely soluble in o-dichlorobenzene at room temperature. The absorption and emission behaviour does not change in the temperature range from 25degreesC to 100degreesC. The fluorescence excitation studies of these poly(1,3,4-oxadiazole)s show a blue emission in solution and in the film. Due to these results the poly(1,3,4-oxadiazole)s are used as electron transport and blue emitting layers in electronic devices like diodes or polymer light emitting diodes (PLED).