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Multiphoton-Excited Serotonin Photochemistry

Department of Chemistry and Biochemistry, The Institute for Cellular and Molecular Biology, and The Center for Nano and Molecular Science and Technology, The University of Texas, Austin, Texas

Correspondence: Address reprint requests to Jason B. Shear, University of Texas, Chemistry and Biochemistry, 1 University Station A5300, Dept. of Chemistry, Austin, TX 78712. Tel.: 512-232-1454; E-mail: jshear{at}mail.utexas.edu.

We report photochemical and photophysical studies of a multiphoton-excited reaction of serotonin that previously has been shown to generate a photoproduct capable of emitting broadly in the visible spectral region. The current studies demonstrate that absorption of near-infrared light by an intermediate state prepared via three-photon absorption enhances the photoproduct formation yield, with the largest action cross sections (10^–19 cm²) observed at the short-wavelength limit of the titanium:sapphire excitation source. The intermediate state is shown to persist for at least tens of nanoseconds and likely to be different from a previously reported oxygen-sensitive intermediate. In addition, the two-photon fluorescence action spectrum for the fluorescent photoproduct was determined and found to have a maximum at 780 nm (3.2 eV). A general mechanism for this photochemical process is proposed.