Intramolecular charge transfer emission of a new ketocyanine dye: Effects of hydrogen bonding and electrolyte

Photophysical and intramolecular charge transfer characteristics of a new ketocyanine dye namely; 2-[3-(4-dimethylaminophenyl)-allylidene]-tetralone (DMAPT) have been studied in organic solvents having different polarities and hydrogen bond donating ability by using steady-state absorption and emission techniques. Spectral data show that increasing solvent polarity results in a significant solvatochromic shift in the absorption maxima and drastic red shifts in the fluorescence maxima, indicating an intramolecular charge transfer character (ICT) of the excited state, and that the solvent-induced dipole moment change is much greater in the excited state than in the ground state. Semiempirical calculations (PM3 and ZINDO/S) were employed to understand the geometric and electronic structure of DMAPT in both ground and excited state. It reveals twisted intramolecular charge transfer character of the excited state due to photoinduced electron transfer from the dimethyl amino group to the carbonyl oxygen. Also, in order to test the sensing properties and control the intramolecular charge transfer interaction of DMAPT, the complexation behavior of DMAPT in ground and excited states with Li+, Mg2+ and Ca2+, has been studied in acetonitrile solutions. The results indicate ground state complex formation between metal ions and the dye. Values of the equilibrium constants for the interaction of metal ions with DMAPT in the S1 state have also been estimated.