Ion-pair charge-transfer complexes of 4-nitrostyrylpyridinium with tetraphenylborate as its counter ion gave fairly stable styrylpyridinyl radicals in 1,2-dimethoxyethane at room temperature due to photoinduced electron transfer reactions between ion pairs. In addition to the remarkable colour changes due to a characteristic absorption of styrylpyridinyl radicals in the visible region, a charge resonance (CR) band was also observed in the near infrared region. The CR band indicated specific 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 association in the dark.