| Abstract
| - We report time-resolved fluorescence data for the anion of p-hydroxybenzylidene dimethylimidazolinone(p-HBDI), a model chromophore of the green fluorescence protein, in viscous glycerol−water mixtures overa range of temperatures, T. The markedly nonexponential decay of the excited electronic state is interpretedwith the aid of an inhomogeneous model possessing a Gaussian coordinate-dependent sink term. A nonlinearleast-squares fitting routine enables us to achieve quantitative fits by adjusting a single activation parameter,which is found to depend linearly on 1/T. We derive an analytic expression for the absolute quantum yield,which is compared with the integrated steady-state fluorescence spectra. The microscopic origins of the modelare discussed in terms of two-dimensional dynamics, coupling the phenyl-ring rotation to a swinging modethat brings this flexible molecule to the proximity of a conical intersection on its multidimensional potentialenergy surface.
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