Estimations of excited state dipole moments of conformers in some o-substituted acetophenones by solvato-chromic shifts.

Ultra violet absorption spectra of o-methylacetophenone, o-fluoroacetophenone and o-hydroxyacetophenone solutions in different solvents are recorded in the region 200-350 nm at room temperature. Excited state dipole moments for three (pi* <-- pi) transitions of the benzene ring for solutions in non-polar and polar solvents are estimated using solvato-chromic shift method [Delta nu against f(epsilon, n)]. The results show that two types of shifts are observed red and blue shifts. The dipole moment values obtained on excitation by red shifted bands in non-polar solvents are much higher than their counterparts both in the ground state and those of the solutions in polar solvents. Those obtained on excitation by blue shifted bands have lower values than ground state, some with same direction and others of reverse direction in both non-polar and polar solvents.