Quantitative description of two-photon absorption with few essential states models

Abstract

We measure two-photon absorption (2PA) spectra and 2PA cross sections in an assortment of different molecules such as substituted diphenylaminostilbenes and push-pull porphyrins using femtosecond fluorescence excitation method. The peak 2PA cross section in the lowest dipole-allowed transition is well described by two level model and can be estimated with better than 50% absolute accuracy from the value of transition dipole moment and permanent dipole moment difference between ground and excited state that we obtain solely from linear spectroscopic measurements. 2PA peaks corresponding to transition to higher energy states are quantitative described by three-level model. We find also that larger value of the permanent dipole moment difference correlates with a smaller value of permanent dipole moment in the electronic ground state.