title: Resonance enhancement of two-photon absorption in fluorescent proteins.
abstract: We measure two-photon absorption (2PA) spectra of wild-type green fluorescent protein, cyan fluorescent protein, and monomeric red fluorescent protein in absolute cross section values in a wide spectral range (lambda2PA = 550 - 1300 nm), and find, for the first time to our knowledge, a new S0 --> Sn 2PA transition in all three proteins in the short-wavelength region. This transition is strongly resonantly enhanced, showing 2PA cross section values of approximately 20-160 GM, which are at least 2-4 times higher than those measured in the lowest energy (S0 --> S1) transition of corresponding proteins. We also show that the change of permanent dipole moment upon S0 --> S1 excitation (|Deltamu10|) can be deduced from 2PA cross section, providing a new tool for fast evaluation of |Deltamu10| in physiological conditions.
authors.affiliation: Department of Physics, Montana, State University, Bozeman, Montana 59717, USA.
authors.forename: M
authors.initials: M
authors.lastname: Drobizhev
authors.forename: N S
authors.initials: NS
authors.lastname: Makarov
authors.forename: T
authors.initials: T
authors.lastname: Hughes
authors.forename: A
authors.initials: A
authors.lastname: Rebane
mesh_terms: D000042:Absorption; D031541:Fluorescence Resonance Energy Transfer; D008164:Luminescent Proteins / Q000737:chemistry*; D017785:Photons; D013053:Spectrophotometry
chemical_list: D008164:Luminescent Proteins