STRUCTURE PHOTOPHYSICS CORRELATIONS IN A SERIES OF 4-(DIALKYLAMINO)STILBENES - INTRAMOLECULAR CHARGE-TRANSFER IN THE EXCITED-STATE AS RELATED TO THE TWIST AROUND THE SINGLE BONDS

4-(Dimethylamino)stilbene and eight regioselectively bridged 4-(dialkylamino)stilbene derivatives have been synthesized and their solvatochromism, fluorescence quantum yields, and lifetimes measured versus the solvent polarity and the temperature. When the single bond connecting the dialkylanilino group to the ethylene group (bond 2) is bridged, strong fluorescence quenching is observed; when this bond is flexible, the fluorescence quenching is strongly reduced, and lifetime maxima at intermediate temperature indicate the involvement of a further TICT emitting state. Fluorescence quenching is reduced in polar solvents and suppressed when the double bond is included in a five-membered carbocyclic ring. This shows that the main deactivating step is connected with twisting of the double bond and that the double-bond twisted state is less polar than the emitting one.