Probing the Ultrafast Photodynamics of Dihydroazulene with In Silico Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction

Molecular photoswitches are chemical systems that can undergo reversible chemical transformations following the absorption of light. Such systems find potential application in modern technologies such as molecular electronics, optical data storage, exploitation of solar energy, and much more. In this paper, we present ab initio nonadiabatic molecular dynamics of the dicyano phenyl-substituted dihydroazulene/vinylheptafulvene (DHA/VHF) system using ab initio multiple spawning in combination with state-averaged α-complete active space self-consistent field theory to study the photoinduced electrocyclic ring opening reaction that converts DHA to VHF. Scrutinizing the mechanism of the photoinduced ring opening reaction is crucial to be able to design new derivatives with improved properties and to design experiments that can probe the photoswitching of such systems. Our simulations show that this DHA system photoswitches with a 41% quantum yield on a sub-picosecond time scale. In addition to that, we simulate the time-resolved photoelectron spectrum, which, by comparison to the experimental equivalent, shows that our dynamics reproduce the experiments with high precision. Furthermore, we simulate the (hitherto unmeasured) elastic ultrafast electron diffraction signal and show that it contains significant features directly related to the nuclear dynamics of the photoswitching event. Our atomistic simulations thus identify ultrafast electron diffraction as an excellent technique for studying the photoswitching of DHA/VHF derivatives and that this could aid in the design and development of new related compounds with optimized switching quantum yields.