NAPHTHALENE-AMINES EXCIPLEX FORMATION PROMOTED BY PHASE-TRANSITION INCRYSTALLIZED CYCLOHEXANE

The effect of the phase transition of cyclohexane at 186 K on the form ation of exciplex in a rigid matrix was studied for the naphthalene (N p)-N,N-dimethylaniline (DMG), Np-N,N-diethylaniline (DEA), Np triethyl amine (TEA), and pyrene (Py)-DMA systems by using a high-resolution fl uorescence spectrometer. AH systems show appearance of an exciplex emi ssion around 186 K. However, a drastic increase in the probability of exciplex formation with the effect of the phase transition of cyclohex ane, which has been previously found by us for the Np-1,2,5-trimethylp yrrole system, was observed only for the Np-DMA and Np-DEA systems. In both of these systems the maximum intensity of the exciplex emission is observed for low concentration of the electron donor molecule, and we have obtained spectral evidences for the formation of solute ''mixe d microcrystallites'' in the low-temperature cyclohexane matrix. The o ccurrence of these:exciplex emissions can be explained by an exciton-a ssisted mechanism taking place in guest mixed crystallites. Proof for the formation of mixed,crystallites was not obtained for the Np-TEA an d Py-DMA systems. TEA seems to have no mutual affinity with Np at low temperature and rather accelerates the creation of Np crystallites. Th us, exciplexes formed in rigid solvent matrix could be categorized int o two types: crystalline type and encounter type.