Photophysics of representative ketocyanine dyes: dependence on molecular structure.

Spectral properties of a new fluorescent ketocyanine dye have been discussed. The energy of maximum absorption/fluorescence of the dye exhibits bathochromic shift with increasing polarity of the medium. Both dipolarity-polarisability and hydrogen bond donation interaction contribute to solvation of the dye. Study of fluorescence parameters points to existence of different emitting states of the dye for aprotic and protic solvents. While the emitting state is the (1)(π, π*) state for aprotic solvents, fluorescence supposedly take place from a different emitting state involving H-bond formation in the excited state in protic solvents. Fluorescence parameters of the dye have been compared with those for a structurally similar symmetric ketocyanine dye. The faster decay of the dye relative to its symmetric counterpart has been explained as due to an increase of nonradiative decay.