Cis–trans photoisomerization properties of GFP chromophore analogs

The photoswitching behaviour of the green fluorescent protein (GFP) chromophore and its analogs opens up exciting horizons for the engineering and development of molecular devices for high sensitivity in vivo studies. In this work we present the synthesis and photophysical study of four GFP chromophore analogs belonging to butenolide and pyrrolinone classes. These chromophores possess an intriguing photoinduced cis–trans isomerization mechanism. Stereochemical structural assignment was unambiguously performed by 1D Nuclear Overhauser Effect NMR measurements. The spectroscopic properties of both cis and trans isomers were studied, and photoconversion quantum yield for cis–trans isomerization was assessed to be in the 0.1–0.4 range. Finally, the 3JC,H coupling constant in the 13C–C=C–H motif was in excellent agreement with theoretical DFT calculations, thus providing a further confirmation of cis–trans photoisomerization of the structurally analog GFP chromophore.