Surface Hopping Molecular Dynamics Simulations for Photophysics and Photoreactions Involving Pyrene and CH3Cl

Pure or halogenated Polycyclic Aromatic Hydrocarbons (PAHs), and saturated halogenated hydrocarbons both are classes of harmful chemicals found in Earth’s atmosphere, often involved in photochemical reactions. On a positive side, the photoreaction of PAHs with halogenated hydrocarbons is a model for and offers routes to, functionalized nano-structured carbon-based materials with tailored optoelectronic properties. Mechanistic studies on photoreactions of these chemicals, possibly with each other, are therefore clearly of interest but still comparatively rare. In the present work, as a representative case study the photophysics (spectra, excited-state lifetimes) and photoreaction dynamics of van der Waals or chemically bound complexes of pyrene (C16H10) and methyl chloride (CH3Cl) were investigated using a combination of computational techniques, this way delivering time- and atom-resolved information on post-excitation processes. Structural optimizations of possible reactants and products as well as excited states and absorption spectra were obtained by semiempirical (AM1) configuration interaction singles (CIS) and (time-dependent) density functional theory (DFT), respectively. Non-adiabatic surface hopping dynamics (NASH) based on AM1-CIS provided excited state lifetimes and were used to explore various photochemical channels of CH3Cl physisorbed or covalently bound to pyrene.