Ultrafast intramolecular charge transfer and dual fluorescence of dimethylamino-substituted triphenylphosphines in polar solvents

Dimethylamino‐substituted triphenylphosphines show a dual fluorescence in polar solvents. The strong red‐shift of the new fluorescence band in solvents of increasing polarity indicates emission from a species of charge transfer character, by analogy with dimethylaminobenzonitrile. In this study, we give evidence for the fast formation of a polar transient species in the first excited state of substituted triphenylphosphines, by picosecond time‐resolved fluorescence and transient absorption spectroscopy. The risetime of the long wavelength fluorescence band is slowed down in solvents of decreasing polarity, and when the number of dimethylamino substituents increases. Furthermore, time‐resolved transient absorption spectra show the rise of a new transient absorption band in polar solvents which has a profile similar to that of the dimethylaniline cation radical.