Dual emission of chalcone-analogue dyes emitting in the red region

The photophysical properties of new synthesized chalcones namely; 1-(4'-R-phenyl)-5-(4'-dimethylaminophenyl)-2,4- pentadien-1-one, [R=H (1), Cl (2) and OCH3 (3)] were studied in different solvents by using steady-state absorption and emission spectroscopy. The fluorescence spectra of these chalcones exhibit dual emission in medium and polar solvents. The dual emission was attributed to population of a polar locally excited (LE) state and a highly dipolar intramolecular charge transfer (ICT) state. The changes in dipole moments upon excitation were calculated from the solvatochromic plots. The total fluorescence quantum yields (of) were also determined, and their values are strongly dependent on the nature of substitutent and the solvent polarity. Semiempirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) method were also performed to investigate the molecular and electronic structures of these chalcones in both the ground and excited state. The change of the dipole moment upon excitation was explained on the basis of changes in the charge redistribution over the whole skeleton of the molecules, which agree well with the experimental results. Also, the nature and energy of the electronic transitions were elucidated and discussed in relation to the experimental data. (C) 2004 Elsevier B.V. All rights reserved.