SiO2 colloidal effects on the twisted intramolecular charge transfer of p-N,N-dimethylaminobenzoic acid in acetonitrile

The twisted intramolecular charge transfer (TICT) in the excited state of p-N,N-dimethylaminobenzoic acid (DMABA) has been investigated in the presence of SiO2 colloids in acetonitrile by using steady-state and time-resolved fluorescence techniques. The SiO2-dependent intensity ratio of the TICT emission to the normal emission clearly demonstrates a distinct phenomenon as a function of SiO2 concentration: an enhancement of the TICT emission occurs upon the addition of 0.3 μM SiO2 whereas a reduction occurs in the presence of excess SiO2 colloids. These results suggest that the formation of the excited TICT state is enhanced by the hydrogen bonding between the carboxylic acid of DMABA and SiO2 colloidal surface.