Influence of interaction of chromophores, linked by the unconjugated chain, on the luminescence properties of biscyanine dyes

Deactivation of electronically excited state of chemically bound dimers - biscyanines with two chromophores linked by unconjugated chains and corresponding monomer dye was investigated. It was found that the quantum yield of dimer fluorescence is lower than that of a monomer dye. The amount of quantum yield of fluorescence decreases with the increase of chromophores interaction degree (the decrease of the isolating polymethylene bridge length). It is shown on the basis of the external heavy-atom effect studies that the decrease of biscyanines fluorescence ability is connected with the enhancement of singlet-triplet intersystem crossing (S-1 --> T-2). It has been established that the probability of the triplet states population in biscyanines with chromophores in parallel arrangement is considerably higher than that in similar compounds with an angular arrangement of chromophores. The delayed fluorescence was observed in the case of dyes with parallel arrangement of chromophores. (C) 2000 Elsevier Science B.V. All rights reserved.