The photophysical and photochemical behavior of several aniline spacer - styrene molecules in which the spacer is a short polymethylene chain has been investigated. Long wavelength excitation selectively excites the aniline chromophore which undergoes intramolecular quenching by the styrene to yield an intramolecular exciplex. Exciplex fluorescence is observed for both of the tertiary anilines investigated and for one of the three secondary anilines. More rapid exciplex formation in nonpolar vs. polar solvents is attributed to the necessity of desolvating the polar aniline singlet in polar solvents. Intramolecular adduct formation is the major photochemical process for the secondary anilines, but is highly inefficient for the tertiary anilines. The behavior of the intramolecular aniline-styrene exciplexes is compared to that of the styrene-amine exciplexes previously investigated in this laboratory.Key words: intramolecular exciplex, fluorescence, aniline, styrene.

The temperature-dependent photochemical behavior of 1,3-diphenylpropene and several of its 3-substituted derivatives has been investigated over a wide temperature range. The singlet state is found to decay via two unactivated processes, fluorescence and intersystem crossing, and two activated processes, trans,cis isomerization and phenyl-vinyl bridging. The latter activated process yields a diradical intermediate which partitions between ground-state reactant and formation of the di-pi-methane rearrangement product. Kinetic modeling of temperature-dependent singlet decay times and quantum yields of fluorescence, isomerization, di-pi-methane rearrangement, and nonradiative decay provides rate constants and activation parameters for each of the primary and secondary processes. Substituents at the 3-position are found to have little effect on the electronic spectra or unactivated fluorescence and intersystem crossing pathways. However, they do effect the activated primary and secondary processes. Thus, the product ratios are highly temperature dependent.

Intramolecular electron transfer and exciplex formation have been investigated for a family of styrenespacer-amine molecules in which the spacer consists of a rigid amide group in the middle of a flexible alkane chain. The amide is connected to the styrene by either one or two methylene units and to a trialkylamine by two to six methylene units. The dependence of electron-transfer kinetics and exciplex formation have been investigated as a function of the length of the spacer, the orientation of the amide, and the amine oxidation potential. Intramolecular quenching of the styrene fluorescence intensity and lifetime is observed for all of the styrene-spacer-amine molecules. Quenching of styrene fluorescence is accompanied by the appearance of intramolecular styrene-amine exciplex fluorescence in nonpolar solvents. The low energy of the exciplex fluorescence emission maximum in nonpolar solvents is attributed to internal solvation by the polar amide group. A maximum in the quantum yield for exciplex fluorescence and minimum in the styrene lifetime is observed for spacers with a total length of seven atoms, including the amide group. This unusual chain length dependence is attributed to the conformational requirements of the amide group.

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