Photoinduced electron transfer and charge resonance band in ion-pair charge-transfer complexes of styrylpyridinium tetraphenylborate

Photoinduced electron transfer reactions were observed at room temperature in organic solvents by steady and flash photolysis of ion-pair charge-transfer complexes between styrylpyridinium derivatives having electron-withdrawing groups at para-position of a styryl group and tetraphenylborates as their counter ions. In addition to the remarkable colour changes due to a characteristic absorption of styrylpyridinyl radicals in the visible region, a charge resonance absorption band (CR band) was observed in the near infrared region depending on the substituent. The latter was due to the electronic interaction of photogenerated neutral radicals with their parent styrylpyridinium cations. The rise of the CR band upon ns laser excitation was as fast as that of the radical itself.