Two-photon electronic spectra of nucleotides

Polarized two-photon fluorescence excitation spectra were obtained for the nucleotides TMP, CMP, GMP, and AMP in neutral aqueous room temperature solution (0.05M). The wavelength range was 400- 600 nm, corresponding to states reached with 200-300 nm single UV photons. INDO/S-CI predictions were carried out for the corresponding methyl bases, and were somewhat useful for the 260 nm bands with certain parameterizations. Theory failed to find the strong two-photon absorption seen below 450 nm, which may be of Rydberg origin.