Fast and slow processes of thermal deactivation of excited stilbazolium merocyanine dyes

The long living triplet states play important role in sensitizing action in all photochemical reactions. The yield of generation of tripler states of dyes can be evaluated on the basis of measurements of their slow (microseco nd) thermal deactivation (TD). All experiments were carried out in the oxyg en presence, it means under quenching dye triplets. The pulse dye laser gen erates in the investigated solution pressure signal. The high of the amplit udes of first maximum of this pressure wave-form signal in the solution of the investigated dye and in the reference sample were measured. Reference s ample exhibits only fast processes of TD. The comparison of the first maxim um of wave- form photothermal signal of sample and of reference enable to c alculate part of energy exchanged into heat in time longer than time resolu tion of arrangement. The fluorescence yields of investigated dyes were also established. On the basis of such data, using procedure described in liter ature, the yield of singlet-tripler intersystem crossing (ISC) was evaluate d. It was shown that this yield depends on the length of stilbazolium meroc yanine chain. The product of triplet state yield and energy was lower for m erocyanines with longer chains. At lower temperatures the yield of fluoresc ence increases and amount of excitation exchanged in short time into heat d ecreases. The slow TD process increases in low temperature because of the d ecrease in the quenching of the dyes triplet states by oxygen. The amount o f energy exchanged into heat in a time longer than time resolution of appar atus is due predominantly through TD of the dye tripler states. (C) 2001 El sevier Science B.V. All rights reserved.