Two-photon absorption spectra of single crystalline anthracene by CARS and CSRS and observation of a charge-transfer band

Two-photon absorption spectra of single crystalline anthracene were obtained by analyzing the CARS and CSRS line shapes of 1262 cm−1 Raman mode in three different polarization schemes. Five two-photon peaks were observed in the energy range 2ω=31 000–41 500 cm−1 and were reasonably assigned to even-parity Frenkel excitons corresponding to the solution data, except a remarkable one at 31 400 cm−1. It was concluded that the last band is most probably assigned to a charge-transfer state of the crystal, by showing that such a two-photon transition can have rather large cross section in contrast with the small value expected for the one-photon transition to the conjugate CT state.