Time-resolved fluorescence intensity and anisotropy decays of 2,5-diphenyloxazole by two-photon excitation and frequency-domain fluorometry

J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, E. Danielsen, M. J. Wirth

Research output: Contribution to journalArticle

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Abstract

We report the first time-resolved fluorescence measurements of the intensity and anisotropy decays resulting from two-photon excitation. A 10-GHz frequency-domain fluorometer (Rev. Sci. Instrum 1990, 61, 2331), equipped with two focal lenses and an emission monochromator, was used for steady-state and time-resolved measurements of PPO fluorescence. The emission spectra and the intensity decays observed with single- and two-photon excitation were essentially identical. The steady-state limiting anisotropy r0 of PPO in glycerol at -5°C measured for two-photon excitation is significantly higher than that observed for one-photon excitation. The r0 value of 0.54 for two-photon excitation is well in excess of the theoretical maximum of 0.4 for single-photon excitation. A similar value of r0 ≃ 0.50 was obtained from the frequency-domain anisotropy data with two-photon excitation of PPO in methanol, butanol, and propylene glycol at 20°C. These higher values of r0 indicate that two-photon excitation results in a more highly oriented photoselected population, which can increase the resolution of rotational correlation times and/or complex anisotropy decays. The anisotropy resolution can still be increased by using global analysis of anisotropy decays measured with single- and two-photon excitation.

Original languageEnglish
Pages (from-to)3000-3006
Number of pages7
JournalJournal of Physical Chemistry
Volume96
Issue number7
DOIs
StatePublished - 1992

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