Photochemical Mechanisms of Hydroxyquinoline Benzimidazole: Insights from Electronic Structure Calculations and Nonadiabatic Dynamics Simulations

Excited-state intramolecular double proton transfer (ESIDPT) has received much attention because of its widespread existence in the life reactions of living organisms, and materials with this property are significant for their special luminescent properties. In this work, the complete active space self-consistent field (CASSCF) and OM2/multireference configuration interaction (OM2/MRCI) methods have been employed to study the static electronic structure calculations of the photochemistry and the possibility of ESIDPT process of hydroxyquinoline benzimidazole (HQB) molecule, along with the nonadiabatic dynamics simulations. The computational results show that the HQB molecule is relaxed to the S1-ENOL minimum after being excited to the Franck-Condon point in the S1 state. Subsequently, during the nonadiabatic deactivation process, the OH···N proton transfer and the twisting of benzimidazole occur before arriving at the single proton transfer conical intersection S1S0-KETO. Finally, the system can either return to the initial ground-state structure S0-ENOL or to the single proton transfer ground-state structure S0-KETO, both of which have almost the same probability. The dynamics simulations also show that no double proton transfer occurs. The excited-state lifetime of HQB is fitted to 1.1 ps, and only 64% of the dynamic trajectories return to the ground state within the 2.0 ps simulation time. We hope the detailed reaction mechanism of the HQB molecule will provide new insights into similar systems.

Crystal structure of 8-[7,8-bis-(4-chloro-benzo-yl)-7H-cyclo-penta-[a]ace-naphthylen-9-yl]naphthalene-1-carb-oxy-lic acid

The title compound packs with a three-dimensional supra­molecular architecture via O—H⋯O, C—H⋯O and C—H⋯Cl hydrogen bonds and through C—H⋯π inter­actions.

The title compound, C₄₀H₂₂Cl₂O₄, was formed by a Michael–Aldol domino reaction sequence, which coupled acenaphthene­quinone with 4-chloro­aceto­phenone in the presence of KOH in methanol. The dihedral angles between the central cyclo­penta­[a]ace­naphthyl­ene fused-ring system (r.m.s. deviation = 0.066 Å) and the 4-chloro­benzoyl rings are 62.25 (10) and 70.19 (10)°. The dihedral angle between the central ring system and the naphthoic acid grouping is 62.46 (7)°. This twisting of the pendant rings facilitates the formation of an intra­molecular aromatic π–π stacking inter­action between the 4-chloro­benzoyl and naphthoic acid rings, with centroid–centroid distances of 3.4533 (16) and 3.5311 (16) Å, and a C—H⋯π inter­action between one of the H atoms of the central moiety and the 4-chloro­benzoyl ring with an H⋯π distance of 2.57 Å. In the crystal, carb­oxy­lic acid inversion dimers generate R₂²(8) loops. The dimers are linked by weak C—H⋯O and C—H⋯Cl hydrogen bonds and C—H⋯π inter­actions, generating a three-dimensional architecture.