EXCITED-STATE DIPOLE-MOMENTS OF SOME COUMARIN DYES FROM A SOLVATOCHROMIC METHOD USING THE SOLVENT POLARITY PARAMETER, E(N)(T)

Excited-state dipole moments of a set of Coumarin dyes extensively use d in laser applications have been determined for the first time, emplo ying a solvatochromic procedure utilising the microscopic solvent pola rity parameter, E(T)(N). Our results are expected to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts is superior to that obtained using bulk solvent polarity funct ions. The experimentally determined dipole-moment changes are in fair agreement with recent semi-empirical computational predictions. It is shown that the discrepancies observed in some cases can be overcome us ing more appropriate parametrisation in the calculation. The insight p rovided by the present measurements into the nature of the emitting st ate is mentioned.