The phosphorescent state of the 1,2,4,5-tetracyanobenzene-naphthalene complex

Abstract

The phosphorescent state of the 1,2,4,5-tetracyanobenzene-naphthalene charge-transfer complex in rigid solution and in single crystal of 1:1 composition was studied in detail through measurements of the phosphorescence, phosphorescence excitation, E.S.R., and microwave-induced delayed phosphorescence spectra. From the analysis of these spectra it is concluded that there are two types of the complexes with different charge-transfer characters both in rigid solution and in crystal. The crystal was found to have three types of phosphorescent sites: Site 1, naphthalene as a shallow trap; Site 2, the complex, the phosphorescent state of which has the character of a locally (within naphthalene) excited triplet state perturbed by the charge-transfer interaction; Site 3, the complex, the phosphorescent state of which is mainly of charge-transfer triplet. Phosphorescence spectra from the individual sites were separately observed with the aid of the microwave-induced delayed phosphorescence technique. The temperature dependence of the phosphorescence spectrum in the crystalline state was explained by considering the energy transfer among these sites. In addition to the three types of phosphorescence, delayed charge-transfer fluorescence due to triplet-triplet annihilation was observed.