Two-Photon Absorption in Anthracene

Abstract

Two-photon transition rates for molecular and crystalline anthracene are calculated using Pariser's $\ensuremath{\pi}$-electron molecular-orbital wave functions, including configuration interaction. Distinctive polarization dependences and approximate rates are obtained for the 4.94-eV ${B}_{1g}$ and 5.00-eV ${A}_{1g}$ molecular states. Frenkel exciton states built from the ${B}_{1g}$ state are found to be sufficiently red-shifted to account for the absorption observed in the solid. The levels found at 3.48 and 3.58 eV by Fr\"ohlich and Mahr are tentatively identified as the ${B}_{g}$ and ${A}_{g}$ components, respectively, of the resulting Davydov doublet. Polarization dependences are consistent with available data, and the calculated rate is of reasonable magnitude. An ${A}_{1g}$-derived doublet is predicted near 4.8 eV.