Stilbene has long been a model system for photochemical isomerization due to the differences in physical properties of cis and trans isomers and their stability in ambient conditions. Photoexcited cis-stilbene may isomerize to form trans-stilbene or cyclize to form 4a,4b-dihydrophenanthrene (DHP). Both pathways involve passage through conical intersections from excited to ground electronic states. The time-resolved photoelectron spectrum of cis-stilbene with a 267 nm pump pulse and a 160 nm probe pulse reveals a complicated band structure within the first 500 fs which cannot be explained by a global decay model. Photoelectron spectra calculated with DFT-MRCI along the barrierless isomerization and cyclization decay pathways reveal a chirp in the photoelectron spectrum, and a combination of the two pathways closely resembles the experimental spectrum. A long lived signal from the formation of DHP is also predicted and experimentally observed at low photoelectron kinetic energies. These results provide an assignment of the photochemistry of cis-stilbene, from photoexcitation to relaxation to the ground state.

Time-resolved photoelectron spectroscopy of cis-stilbene: Theory and experiment

2019 Spring National Meeting

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