CHAIN-LENGTH-DEPENDENT AND SOLVENT-DEPENDENT INTRAMOLECULAR PROTON-TRANSFER IN STYRENE AMINE EXCIPLEXES

The photochemical and photophysical behavior of several ((N,N-dimethyl amino)alkyl)styrenes in which the amino group is attached to the styre ne alpha- or beta-carbon by a methyl, ethyl, propyl, or butyl polymeth ylene chain has been investigated. Efficient intramolecular addition o f an aminomethyl C-H to styrene is observed in nonpolar solvents for t he (aminoethyl)styrenes, and addition of anaminomethylene C-H is obser ved for the (aminobutyl) styrenes. However, the (aminomethyl)- and (am inopropyl)styrenes do not undergo intramolecular addition reactions. B oth the reactive and unreactive (aminoalkyl)styrenes form fluorescent singlet exciplexes in nonpolar and polar solvents. The results of exci plex and product quenching by an added primary amine indicate that the fluorescent exciplex is an intermediate in the addition reactions of the (aminoalkyl)styrenes. Activation parameters for both exciplex form ation and exciplex proton transfer have been determined. Highly regios elective intramolecular proton transfer is proposed to occur via least motion pathways from the lowest energy folded conformations of the si nglet exciplex intermediates in nonpolar solvents. The solvent depende nce of exciplex proton transfer, fluorescence, intersystem crossing, a nd nonradiative decay is attributed to a change in exciplex conformati on from folded in nonpolar solvents to extended in solvents more polar than diethyl ether.