Excited state intramolecular charge transfer process in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid ethyl ester and effect of acceptor functional groups

Excited state intramolecular charge transfer (ICT) process in a donor–chromophore–acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid ethyl ester (DMAPPDE) has been investigated spectroscopically in combination with quantum chemical calculations. The molecule DMAPPDE shows dual fluorescence corresponding to emission from the locally excited as well as charge transfer states in polar solvents. Large solvatochromic shift of emission band (Δν = 8504 cm−1), high excited state dipole moment (18 D), quantum chemically calculated potential energy curves by Density Functional Theory (DFT) method and HOMO–LUMO pictures support the occurrence of excited state ICT process. Variation of acceptor strength in this molecular system shows prominent effect on the spectroscopic and molecular properties like absorption and emission band maxima, Stokes’ shift, quantum yields, and dipole moment which are found to be controlled by the ICT process.