Simulation and analysis of the relaxation dynamics of a photochromic furylfulgide

Furylfulgides, a class of photochromic organic compounds, show a complex system of photoinduced reactions. In the present study, the excited-state dynamics of the E α and E β isomers of a representative furylfulgide is modelled with the use of nonadiabatic molecular dynamics simulations. Moreover, a pattern recognition algorithm is employed in order to automatically identify relaxation pathways, and to quantify the photoproduct distributions. The simulation results indicate that, despite differing only in the orientation of the furyl group, the two isomers show markedly different photochemical behaviour. The predominant E α isomer undergoes photocyclisation with a quantum yield (QY) of 0.27 ± 0.10. For this isomer, the undesired E → Z photoisomerisation around the central double bond represents a minor side reaction, with a QY of 0.09 ± 0.07. In contrast, the minority E β isomer, which is incapable of photocyclisation, undergoes efficient E → Z photoisomerisation, with a QY as high as 0.56 ± 0.14. The relaxation kinetics and the photoproduct distributions are interpreted in the light of the available experimental data. The complex photochemistry of a model furylfulgide is resolved with a combination of nonadiabatic molecular simulations and pattern recognition analysis of molecular geometry.