Abstract

Dynamical behavior of 3-(2-Benzimidazolyl)-7-(DiethylAmino) coumarin [coumarin7 (C7)] and 3-(2-N-Methylbenzimidazolyl)-7-N, N-diethylamino coumarin [coumarin30 (C30)] laser dyes have been examined in methanol as a function of temperature. It is observed that, the rotational motion of probe molecule in methanol solvent increases as the temperature increase. We also investigated that, C30 rotates faster than C7 in the same solvent. It is all due to the friction between solute and solvent, diffusion and hydrogen bonding establish between alcoholic group and coumarin molecule. We have also determined the excited state and ground state dipole moments in alcoholic series solvents by using Bakhshiev, Chamma-viallet equations and Quantum mechanical treatment. From the results, it is found that, excited state dipole moment is greater than the ground state dipole moment, which indicates that excited state is more polar than the ground state.

Key words: Coumarin7 (C7), coumarin30 (C30), reorientation time, fluorescence time, stokes shift, dipole moment, rotational diffusion, dielectric friction.