Detailed Photoisomerization Dynamics of a Green Fluorescent Protein Chromophore Based Molecular Switch

With density-functional-based nonadiabatic molecular dynamics simulations,trans-to-cisandcis-to-transphotoisomerizations of a green fluorescent protein chromophore based molecule 4-benzylidene-2-methyloxazol-5(4H)-one (BMH) induced by the excitation to itsS1excited state were performed. We find a quantum yield of 32% for thetrans-to-cisphotoisomerization of BMH and a quantum yield of 33% for itscis-to-transphotoisomerization. For those simulations that did producetrans-to-cisisomerization, the averageS1excited state lifetime oftrans-BMH is about 1460 fs, which is much shorter than that ofcis-BMH (3100 fs) in those simulations that did producecis-to-transisomerization. For both photoisomerization processes, rotation around the central C2=C3 bond is the dominant reaction mechanism. Deexcitation occurs at an avoided crossing near theS1/S0conical intersection, which is near the midpoint of the rotation.