Journal of Photoscience

Korean Society of Photoscience (한국광과학회)
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EXCITED-STATE INTRAMOLECULAR PROTON TRANSFER IN DICOUMAROL, A $CH_2$-BRIDGED DIMER OF 4-HYDROXYCOUMARIN

  • Cho, Dae-Won (Department of Chemistry, Chungnam National University)
  • Published : 1995.03.01
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Abstract

The steady-state emission spectra of dicoumarol (DC) in ethanol and EPA have been examined at various temperatures (77-298 K). At room temperature, a fluorescence spectrum of DC in ethanol shows a emission maximum at 350 nm. In EPA a Stokes-shifted emission band appears around 470 nm in addition to the 350 nm emission, and its intensity is enhanced as temperature decreases. This emission is attributed to a zwitterionic tautomer of DC formed by a single excited-state intramolecular proton transfer (ESIPT) along the internal hydrogen-bonding. The fluorescence lifetimes have been measured at 350 and 450 nm as a function of temperature. The fluorescence decay at 350 nm is single exponential at any temperature, whereas the one at 450 nm becomes biexponential at temperatures below 250 K. These results are discussed in terms of a conformational change followed by the ESIPT. The activation energy barrier for the conformational change has been determined to be 3.7 $\pm$ 0.2 kJ/mole.

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