We report new, detailed, femtosecond time-resolved photoelectron spectroscopy experiments and calculations investigating the competition between ultrafast internal conversion and ultrafast intersystem crossing in electronically and vibrationally excited benzene at the onset of "channel 3". Using different probe energies to record the total photoelectron yield as a function of pump-probe delay we are able to confirm that S 1 , T 1 and T 2 electronic states are involved in the excited state dynamics. Time-resolved photoelectron spectroscopy measurements then allow us to unravel the evolution of the

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The green fluorescent protein (GFP) is employed extensively as a marker in biology and the life sciences as a result of its spectacular fluorescence properties. Here, we employ femtosecond time-resolved photoelectron spectroscopy to investigate the ultrafast excited state dynamics of the isolated GFP chromophore anion. Excited state population is found to decay bi-exponentially, with characteristic lifetimes of 330 fs and 1.4 ps. Distinct photoelectron spectra can be assigned to each of these timescales and point to the presence of a transient intermediate along the decay coordinate. Guided by ab initio calculations, we assign these observations to twisting about the CC -C bridge followed by internal conversion to the anion ground state. The dynamics in vacuo are very similar to those observed in solution, despite the difference in absorption spectra between the two media. This is consistent with the protein environment restricting rotation about the CC -C bond in order to prevent ultrafast internal conversion and preserve the fluorescence.

By uncovering the mechanism of UV resonant electron emission, we show that the GFP biomimetics are more stable to photooxidation.

Femtosecond time-resolved photoelectron imaging is employed to investigate ultrafast electronic relaxation in aniline, a prototypical aromatic amine. The molecule is excited at wavelengths between 269 and 238 nm. We observe that the S2(pi3s/pi sigma*) state is populated directly during the excitation process at all wavelengths and that the population bifurcates to two decay pathways. One of these involves ultrafast relaxation from the Rydberg component of S2(pi3s/pi sigma*) to the S1(Pi Pi)* state, from which it relaxes back to the electronic ground state on a much longer timescale. The other appears to involve motion along the pi sigma* dissociative potential energy surface. At higher excitation energies, the dominant excitation is to the S3(pi pi*) state, which undergoes extremely efficient electronic relaxation back to the ground state. Our study supports some conclusions reached from H-atom photofragment translational spectroscopy measurements and pump-probe photoionization measurements and contradicts some others.