Primary events in the photoactive yellow protein chromophore in solution

The photoinduced cis–trans isomerization of the photoactive yellow protein chromophore, the deprotonated trans-p-coumaric acid, is studied in solution by subpicosecond transient absorption and gain spectroscopy. A nonemissive photoproduct absorbing in the UV region, attributed to the cis isomer, is found to appear in 10 ps at the rate of the excited-state decay, demonstrating that there is no detectable intermediate in the relaxation pathway of the photoactive yellow protein chromophore in solution.