title: Two-photon excitation of 4'-hydroxymethyl-4,5',8-trimethylpsoralen.
abstract: Psoralens are a class of pharmaceutical agents commonly used to treat several cutaneous disorders. When irradiated with a mode-locked titanium: sapphire (Ti:sapphire) laser tuned to 730 nm, an aqueous solution of 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) emits blue light. The emission spectrum is centered at 452 nm and is identical to that obtained by one-photon excitation with UVA excitation, and its magnitude depends quadratically on the intensity of laser excitation. These results suggest that two-photon excitation occurs to a potentially photochemically active state. To estimate the two-photon absorption cross section, it was first necessary to measure the emission quantum yield of HMT using 365 nm excitation at room temperature that resulted in a value of 0.045 +/- 0.007. The two-photon absorption cross section of HMT at 730 nm is therefore estimated to be 20 x 10(-50) cm4 s (20 Göppert-Mayer). The excited-state photophysics and photochemistry of psoralens suggest potential applications to cutaneous phototherapy in diseases such as psoriasis and dystrophic epidermolysis bullosa.
authors.affiliation: Department of Dermatology, Stanford University Medical Center, CA 94305-5334, USA. oh_d@hosp.stanford.edu
authors.forename: D H
authors.initials: DH
authors.lastname: Oh
authors.forename: R J
authors.initials: RJ
authors.lastname: Stanley
authors.forename: M
authors.initials: M
authors.lastname: Lin
authors.forename: W K
authors.initials: WK
authors.lastname: Hoeffler
authors.forename: S G
authors.initials: SG
authors.lastname: Boxer
authors.forename: M W
authors.initials: MW
authors.lastname: Berns
authors.forename: E A
authors.initials: EA
authors.lastname: Bauer
mesh_terms: D000537:Aluminum Oxide; D007834:Lasers; D012235:Rhodamines; D013054:Spectrophotometry, Atomic; D014307:Trioxsalen / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D012235:Rhodamines; C016507:hydroxymethyltrioxsalen; C029773:rhodamine B; D000537:Aluminum Oxide; D014307:Trioxsalen