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 language | English |
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Pages (from-to) | 3000-3006 |
Number of pages | 7 |
Journal | Journal of Physical Chemistry |
Volume | 96 |
Issue number | 7 |
DOIs | |
State | Published - 1992 |