Two-photon absorption cross-sections of reference dyes: a critical examination.

The electronic structure and one- and two-photon absorption spectra of four fluorophores, p-bis(o-methoxystyryl)benzene (Bis-MSB), coumarin 307, fluorescein and rhodamine B, commonly used as reference compounds for two-photon absorption spectra, have been theoretically calculated and compared with available experimental data. The possible reasons for the wide discrepancies in two-photon absorption cross-sections reported in the literature are discussed on the basis of the theoretical findings. The role of a solvent environment on the electronic one- and two-photon absorption spectra is also studied. We highlight some necessary precautions that one needs to take when comparing literature results of two-photon absorption cross-sections.