Microhydration of small protonated polyaromatic hydrocarbons: a first principles study

Using first principles methodology, we investigate the microsolvation of protonated benzene (BzH⁺), protonated coronene (CorH⁺) and protonated dodecabenzocoronene (DbcH⁺). Gas phase complexes of these small protonated polyaromatic hydrocarbons (H⁺PAHs) with mono-, di-, and tri-hydrated water molecules are considered. Their most stable forms are presented, where we discuss their structural, energetic aromaticity and IR and UV spectral features. In particular, we focus on the analysis of the bonding and various non-bonded interactions between these protonated aromatics and water clusters. The strength of non-bonded interactions is quantified and correlated with their electron density profiles. Furthermore, insights into the interfacial interactions and stability of these complexes were obtained through non-covalent index and symmetry-adapted perturbation theory (SAPT0) analyses. We also discuss the effects of the extension of the π aromatic cloud on the water solvation of these protonated aromatics. In particular, we extended our predictions for the S₀ → S₁ and S₀ → T₁ wavelength transitions of micro hydrated H⁺PAHs to deduce those of these species solvated in aqueous solution. The present findings should be useful for understanding, at the microscopic level, the effects of water interacting with H⁺PAHs, which are relevant for organic chemistry, astrochemistry, atmospheric chemistry, combustion and materials science.