Incoherent energy migration in optically active J-aggregates

摘要

Depending on the nitrogen substituents of the 5,5',6,6'-tetrachlorobenzimidacarbocyanine chromophore 1 two basically different types of J-aggregates are formed. One type having a single J-absorption band, like TDBC, shows the phenomenon of coherent energy migration well characterized by time-resolved spectroscopy in the past. The other type exhibits a Davydov-splitted J-absorption band whose spectroscopical features, like the non-exponential fluorescence decay, the decrease of its fluorescence lifetime with intreasing temperature, the strong dependence of its fluorescence lifetime on the emission wavelenght, the dependence of the position and shape of its fluorescence spectrum on the time delay of measurement, the pressure dependence of its absorption spectrum, and its optical activity cannot be understood on the basis of coherent energy migration. A consistent description of all properties observed provides the theory of incoherent energy migration. Presumedily it is the degree of disorder which determines the kind of energy migration.