Evidence of an ion-pair charge-transfer complex between 9,10-dicyanoanthracene and 1,4-dimethylnaphthalene in acetonitrile, studied by photoinduced charge-recombination luminescence and by direct photoexcitation luminescence techniques

Abstract

Photoinduced charge-recombination luminescence studies of preirradiated solid solutions of 9,10-dicyanoanthracene (DCA) and 1,4-dimethylnaphthalene (DMN) in acetonitrile at 77 K indicate that in this polar solvent the excited charge-transfer complex formed between DCA and DMN is an ion-pair form which dissociates into DCA^–˙ and DMN⁺˙ upon irradiation at 420 nm. These results complement reported e.s.r. and optical absorption data and further support the postulate of photogeneration of radical ions (DCA^–˙ and DMN⁺˙) as intermediates in polar solvents for the DCA-sensitized photo-oxygenation of DMN. Phosphorescence and fluorescence techniques give evidence of the formation of a charge-transfer complex upon excitation, with DMN as donor and DCA as acceptor. The formation of O₂^–˙ and ¹O₂* proceeds from this excited charge-transfer complex.