Abstract
Using a combination of photoelectron spectroscopy measurements and quantum chemistry calculations, we have identified competing electron emission processes that contribute to the 350-315 nm photoelectron spectra of the deprotonated green fluorescent protein chromophore anion, p-hydroxybenzylidene-2,3-dimethylimidazolinone. As well as direct electron detachment from S0, we observe resonant excitation of the 2(1)ππ* state of the anion followed by autodetachment. The experimental photoelectron spectra are found to be significantly broader than photoelectron spectrum calculated using the Franck-Condon method and we attribute this to rapid (∼10 fs) vibrational decoherence, or intramolecular vibrational energy redistribution, within the neutral radical.
Highlights
Nature has developed a myriad of highly efficient photoactive proteins for gathering energy for chemical processes and initiating specific actions
In order to understand the photophysics of green fluorescent protein (GFP), a good starting point is the isolated model chromophore, p-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) (Fig. 1)
The vertical axes of the spectra have been scaled so that the low electron binding energy (eBE) edges are superimposed on one another and it is clear that the threshold for photodetachment is eKE
Summary
Nature has developed a myriad of highly efficient photoactive proteins for gathering energy for chemical processes and initiating specific actions. A well-known example is the green fluorescent protein (GFP) that was first found in the jellyfish Aequorea victoria.. An example that is relevant to the work presented in this paper is its ability to act as a light-induced electron donor with the potential to monitor and manipulate redox processes in cells.. The chromophore exists in neutral and anionic (deprotonated) forms that both absorb visible light.. Studies of HBDI have revealed that the electronic absorption spectrum of the deprotonated chromophore anion in the gas phase is remarkably similar to that in the protein.. In the gas phase, the deprotonated chromophore anion does not fluoresce and its excited state lifetime has been found to be very similar to that in solution. Studies of HBDI have revealed that the electronic absorption spectrum of the deprotonated chromophore anion in the gas phase is remarkably similar to that in the protein. in the gas phase, the deprotonated chromophore anion does not fluoresce and its excited state lifetime has been found to be very similar to that in solution.
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