Spectroscopy and Excited-State Dynamics of Methyl\nFerulate in Molecular Beams

The spectroscopic\nand dynamic properties of methyl ferulatea\nnaturally occurring ultraviolet-protecting filterand microsolvated\nmethyl ferulate have been studied under molecular beam conditions\nusing resonance-enhanced multiphoton ionization spectroscopy in combination\nwith quantum chemical calculations. We demonstrate and rationalize\nhow the phenyl substitution pattern affects the state ordering of\nthe lower excited singlet state manifold and what the underlying reason\nis for the conformation-dependent Franck-Condon (FC) activity in the\nUV-excitation spectra. Studies on microsolvated methyl ferulate reveal\npotential coordination sites and the influence of such coordination\non the spectroscopic properties. Our quantum chemical studies also\nenable us to obtain a quantitative understanding of the dominant excited-state\ndecay routes of the photoexcited ππ* state involving a\n∼3 ns intersystem crossing pathway to the triplet manifoldwhich\nis much slower than found for coumaratesand a relatively fast\nintersystem crossing back to the ground state (∼30 ns). We\nshow that a common <i>T</i><sub>1</sub>/<i>S</i><sub>0</sub> crossing can very well explain the observation that <i>T</i><sub>1</sub> lifetimes are quasi-independent of the phenyl\nsubstitution pattern.