title: One- and two-photon fluorescence anisotropy of selected fluorene derivatives.
abstract: The steady-state excitation anisotropy spectra of fluorene derivatives were measured in viscous solvents, under the one- and two-photon excitation, over a broad spectral range (UV-Visible). The orientation of their absorption transition moments for the first, S0 --> S1, and second, S0 --> S2, excited states were determined. It was shown experimentally that a decrease in the angle between S0 --> S1 and S0 --> S2 transitions corresponded to an increased value of two-photon absorption (2PA) cross section for these molecules. Two-photon excitation anisotropy was nearly constant over the spectral region investigated (in contrast to one-photon excitation anisotropy spectra) and can be roughly explained by a simple model of 2PA based on the single intermediate state approximation. For comparison, the same trend in two-photon excitation anisotropy was observed for Rhodamine B in glycerol.
authors.affiliation: Department of Chemistry, University of Central Florida, Orlando, Florida, USA. kbelfiel@mail.ucf.edu
authors.forename: K D
authors.initials: KD
authors.lastname: Belfield
authors.forename: M V
authors.initials: MV
authors.lastname: Bondar
authors.forename: J M
authors.initials: JM
authors.lastname: Hales
authors.forename: A R
authors.initials: AR
authors.lastname: Morales
authors.forename: O V
authors.initials: OV
authors.lastname: Przhonska
authors.forename: K J
authors.initials: KJ
authors.lastname: Schafer