STOICHIOMETRIC-DEPENDENT INTRAMOLECULAR CHARGE-TRANSFER FLUORESCENCE OF P-DIMETHYLAMINOCHALCONE IN BETA-CYCLODEXTRIN HOST-GUEST SYSTEMS

Steady state fluorescence and absorption spectra of p-dimethylaninochalcone (DMAC) in aqueous beta-cyclodextrin (beta-CD) solution are reported. The fluorescence maximum of DMAC initially shifts to the red and then to the blue on addition of beta-CD, accompanied by a progressive increase in the relative fluorescence quantum yield. The variation in the absorption maximum of DMAC with beta-CD concentration is in the same direction as that of the fluorescence maximum, but at a lower rate and the absorbance is nearly constant. A double reciprocal plot indicates that the spectral shifts are due to different stoichiometries in the DMAC-beta-CD inclusion complex: the red shift is associated with a 1:1 (guest-host) complex, while the blue shift is due to a 1:2 complex. The effect of beta-CD on the intramolecular charge transfer photophysics of DMAC is discussed within the framework of the three excited state (E*, P* and A* or TICT) model; the channel to the non-fluorescent state P* is blocked on formation of the DMAC-beta-CD inclusion complex.