The influence of donor-acceptor groups on the excited-state dynamics of ethylenic molecules

Conical intersections (CIs) govern molecular dynamics in many light-driven processes, such as vision or photophysics. The non-adiabatic dynamics of ethylene, the simplest double-bond containing molecule, has been extensively investigated as a model system: after initial excitation to the ππ* state, the molecule deforms on its way to the CI - it simultaneously twists along the C=C bond and pyramidalizes on one of the carbons, before returning to a vibrationally hot ground state. The pyramidalization is also associated with an increase in electron density: can we, by changing the electron density on either side of the double bond a priori of the dynamics, control and tune the photophysics of ethylene? To answer this question, we explored the excited-state dynamics of a series of donor-acceptor substituted ethylenes, namely acrylonitrile (acceptor-substituted), methylvinylether (donor-substituted) and 3-methoxyacrylonitrile (donor and acceptor substituted). This joint time-resolved photoelectron spectroscopy and ab initio molecular simulation investigation demonstrates both experimentally and theoretically the fascinating involvement of the donor-acceptor groups in the excited-state dynamics of the double bond.