SOLVENT DEPENDENT FLUORESCENCE LIFETIMES AND MOLECULAR REORIENTATION TIMES FOR ROSE BENGAL

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1977

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Ohio State University

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Abstract

We report picosecond fluorescence lifetimes and excited state molecular reorientation times for the fluorescein dye, Rose Bengal, in a variety of solvents. The timing technique uses time correlated photon counting with our mode-locked, cavity dumped, dye laser excitation. We have established a reliable deconvolution limit of approximately 80 psec for accurate lifetimes using our technique with conventional photomultipliers. We can obtain two exponential decays, such as observed in reorientation measurements, for pairs of lifetimes that differ by a factor of 2-3 or longer. The Rose Bengal molecule has a lifetime of 114, 525, 710, 925, and 750 psec for the solvents $H_{2}O$ , methanol, ethanol, 1-propanol, isopropanol, and 1-butanol, respectively. The reason, for the solvent dependent lifetime can only be established with more measurements. Our initial set of data for molecular reorientation suggests that reorientation times correlate with solvent viscosity and are shorter than the observed lifetimes.

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This work is supported by the National Science Foundation.
Author Institution: Department of Chemistry, Northwestern University

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