Excited state dynamics of a PYP chromophore model system explored with ultrafast infrared spectroscopy

We perform ultrafast polarization sensitive visible pump-infrared probe spectroscopy on deprotonated trans-S-phenyl-thio-p-hydroxycinnamate, a model compound for photoactive yellow protein. We derive structural information from the observed bleach signals by comparison of the experimental frequency positions and anisotropies with results from quantum chemical calculations. The electronically excited state decays with 8 or 15 ps time constants for 1:1 or 10:1 DMSO:buffer, respectively, with a quantum yield for isomerization product formation less than 5%. Comparison of our results with earlier reported work on model compounds and on photoactive yellow protein (PYP) suggests an intricate tuning mechanism of the protein environment for the relaxation dynamics of PYP.