Role of nonfluorescent twisted intramolecular charge transfer state on the photophysical behavior of aminophthalimide dyes

Abstract

Photophysical behavior of 4-aminophthalimide and its N,N-dimethyl derivative is studied in a series of solvents. A comparison of the fluorescence properties of the two compounds reveals that they behave quite differently despite their structural similarity. The efficient nonradiative decay of the dimethyl derivative in polar media is interpreted in terms of a nonemitting twisted state. Semiempirical calculations based on the AM1 method have been performed, and the results support the twisting mechanism. Calculations of the ground and excited state profiles as a function of torsion angle provide a clear picture of whether the twisting can influence the photophysical behavior of this class of dyes. The results provide insight into the design of efficient dye systems. © 1996 American Chemical Society.