FLUORESCENT PROBING OF THE RESTRICTION BY AQUEOUS MICELLES OF THE FORMATION OF THE PHOTOINDUCED BIRADICAL STATE P-ASTERISK OF 4-(DIMETHYLAMINO)CHALCONE

The fluorescence emission of 4-(dimethylamino)chalcone (DMAC) in ionic micellar solutions is examined and discussed in a three-state (E*, A*, and P*) dynamic scheme in an attempt to investigate the formation of the photoinduced biradical state P* in micelles. The emission of DMAC in micelles is mainly from state A* with some from state E*. An extraordinarily high enhancement of the DMAC emission in micelles is observed when in comparison with that of a TICT (twisted intramolecular charge transfer) fluorophore whose excited state consists of two states, LE (locally excited state) and TICT, which correspond to states E* and A*, respectively, while the absorption of DMAC is only slightly strengthened in micelles. The formation of state P* is shown to be restricted in micelles through the blocking of the twisting of the double bond by the high viscosity in the micellar phase. The medium polarity appears to play a relatively minor role in the formation of state P*. The micellar interfacial electric field also exerts an effect, a stronger electric field, favoring the formation of state P*. The dramatic enhancement of the DMAC emission in micelles makes DMAC a potential and feasible fluorescent probe for micelle formation.