Tracking the Charge Transfer State of the Model GFP Chromophore using Transient Grating Photoluminescence Spectroscopy

The green fluorescent protein chromophore led to new methodologies in cell and life sciences. Scientists encoded the protein into biological entities for fluorescence. The green fluorescent protein emitted light concurrently to cellular events. However, the emissive chromophore inside the green protein also interested academics. Specifically, “why the chromophore has lower fluorescence quantum yield outside of the beta-barrel protein?” Relaxation dynamics were important for the anionic model chromophore in basic aqueous solution, and in viscous glycerol solution. With modern instrumentation, broadband ultrafast fluorescence spectroscopy (via the transient grating method) and transient absorption spectroscopy found a specific excitation state within 400 fs till 1-2 picoseconds before a ground state relaxation. Also, the slower timescales in glycerol confirmed the importance of ring-twisting in the chromophore outside the protein.