Dipole moments of laser coumarins in the ground and excited electronic states

Electric dipole moments of the six most effective laser coumarins C1, C4, C 7, C30, C120, and C334 are measured in the equilibrium ground state, excite d Franck-Condon state, and equilibrium excited state in cyclohexane and dio xane by the methods of electrooptical absorption and integrated electroopti cal emission. It is found that parameters of C7 and C30 differ substantiall y from those of the rest of the coumarins. Spectral dependences of the elec trooptical coefficients of solutions of C7 and C30 in cyclohexane and dioxa ne show that at least two electronic transitions contribute to the first ab sorption band. It is most probable that there are two closely lying singlet states of C7 and C30, one of them being nonfluorescent. The results of our studies of solutions of coumarins in cyclohexane and dioxane do not confir m the existence of the intramolecular charge transfer accompanied by a rota tion of the molecular structure after excitation.