Solvent effects on the photochemistry of a ketocyanine dye and its functional analogue, Michler`s ketone

Spectral properties of a photosensitizer, a ketocyanine dye, 2,5-bis([4-(diethylamino)phenyl]methylene)cyclopentanone DEAW, were examined in seven different solvents. The absorption and emission spectra, transient absorption spectra, and conductivity data are reported. Extinction coefficient of the triplet-triplet absorption is calculated using the singlet depletion method. The quantum yield of the triplet state is calculated and is found to have a value from 0.01 to 0.60 in different solvents studied using both 308- and 480-nm pulsed laser excitations. The quantum yield of fluorescence is also reported. The dipole moment of the excited singlet state is calculated using the energy gap between the absorption and emission bands in different solvents of similar refractive indices. Comparison is made with Michler`s ketone (MK) in the discussion of photochemical processes because of the similarity in the structures of DEAW and MK, the only difference being the extended conjugation introduced by the methylene groups along with the cyclopentanone in DEAW.