Regioselective and Solvent-Dependent Photoisomerization Induced Internal Conversion in Red Fluorescent Protein Chromophore Analogues.

Photophysical properties of three red fluorescent protein (RFP) chromophore analogues are reported here. The three RFP chromophore analogues differ in the additional conjugation present in the RFP chromophore. The three chromophores do not exhibit any solvent effect in both absorption and fluorescence spectra. The photoirradiation experiments and recording of 1H NMR before and after irradiation on one of the three RFP model chromophores show isomerization of the (Z,E) diastereomer to the (E,E) diastereomer. Calculation of S0 and S1 potential energy curves shows the preference for isomerization through the exocyclic C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 C bond with Z-stereochemistry, thus corroborating the experimental results. The computational studies also suggest that torsional motion along the exocyclic CC bond pushes the molecules to a conical intersection, thus paving the pathway for radiationless deactivation. Red fluorescent protein (RFP) chromophore analogues exhibit solvent dependent and regioselective photoisomerization, which triggers internal conversion through conical intersection.