SPECIFIC INTERACTION OF 4-NITROSTYRYLPYRIDINIUM IONS UPON PHOTOEXCITATION IN SOLUTIONS

Ion-pair charge-transfer complexes of 4-nitrostyrylpyridinium with tet raphenylborate as its counter ion gave fairly stable styrylpyridinyl r adicals in 1,2-dimethoxyethane at room temperature due to photoinduced electron transfer reactions between ion pairs. In addition to the rem arkable colour changes due to a characteristic absorption of styrylpyr idinyl radicals in the visible region, a charge resonance (CR) band wa s also observed in the near infrared region. The CR band indicated spe cific interaction of photogenerated neutral radicals with their parent styrylpyridinium cations. Prolonged irradiation and/or storage in the dark after irradiation caused further colour changes depending on the initial concentrations and irradiation times. These results indicated that nitrostyrylpyridinyl radicals had stronger tendency of associati on in the dark.