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Deactivation Mechanism of the Green Fluorescent Chromophore Rinat Gepshtein, Dan Huppert, and Noam Agmon*,

Summary: Deactivation Mechanism of the Green Fluorescent Chromophore
Rinat Gepshtein, Dan Huppert, and Noam Agmon*,
Raymond and BeVerly Sackler Faculty of Exact Sciences, School of Chemistry, Tel AViV UniVersity,
Tel AViV 69978, Israel, and Department of Physical Chemistry and the Fritz Haber Research Center,
The Hebrew UniVersity, Jerusalem 91904, Israel
ReceiVed: July 20, 2005; In Final Form: December 22, 2005
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 over
a range of temperatures, T. The markedly nonexponential decay of the excited electronic state is interpreted
with the aid of an inhomogeneous model possessing a Gaussian coordinate-dependent sink term. A nonlinear
least-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 model
are discussed in terms of two-dimensional dynamics, coupling the phenyl-ring rotation to a swinging mode
that brings this flexible molecule to the proximity of a conical intersection on its multidimensional potential
energy surface.
1. Introduction
The green fluorescent protein (GFP) has attracted great
interest as a biological fluorescence marker.1-3 Its p-hydroxy-
benzylidene imidazolinone chromophore (Cro) forms posttrans-


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry