Relationship between excited- and ground-state dipole-moment differences and femtosecond second hyperpolarizabilities for molecules with large intramolecular charge-transfer

Summary form only given. We report that intramolecular charge transfer (ICT) molecules with a great difference between the permanent electric dipole moment of the excited state and that of the ground state have highly nonlinear electronic polarization even in the nonresonant region, and the third-order nonlinearity responds instantaneously within the duration of the femtosecond pump pulse. Furthermore, it is found experimentally that the angular-averaged second hyperpolarizability indicates a parabolic dependence as an increasing function of the dipole-moment difference over a wide range.