A study on the intramolecular charge transfer and the photophysical behavior of 2,4,6-trisubstituted pyrylium salt

A series of 2,4,6-trisubstituted pyrylium compounds were synthesized and their photophysical behavior in solvents with different polarities was measured. It was found that both properties (donor or acceptor) and positions (x- or y-band) of the substituents have a great influence on the luminescence behavior of these compounds. It was proved by the fluorescence depolarization method that intramolecular conversion may occur between the x- and y-chromophores in 2,4,6-trisubstituted pyryliums. It was also found that pyrylium compounds with N,N-dimethylamino phenyl groups could be used as fluorescence indicators in a non-aqueous solution due to the dramatic change of fluorescence intensity arising from the transformation of a tertiary amine into a quaternary ammonium salt by the addition of acids.