Intermolecular dissociation energies of dispersively bound 1-naphthol⋅cycloalkane complexes

Intermolecular dissociation energies D₀(S₀) of the supersonic jet-cooled complexes of 1-naphthol (1NpOH) with cyclopentane, cyclohexane, and cycloheptane were determined to within <0.5% using the stimulated-emission pumping resonant two-photon ionization method. The ground state D₀(S₀) values are bracketed as 20.23±0.07 kJ/mol for 1NpOH⋅cyclopentane, 20.34±0.04 kJ/mol for 1NpOH⋅cyclohexane, and 22.07±0.10 kJ/mol for two isomers of 1NpOH⋅cycloheptane. Upon S₀→S₁ excitation of the 1-naphthol chromophore, the dissociation energies of the 1NpOH⋅cycloalkane complexes increase from 0.1% to 3%. Three dispersion-corrected density functional theory (DFT) methods predict that the cycloalkane moieties are dispersively bound to the naphthol face via London-type interactions, similar to the "face" isomer of the 1-naphthol⋅cyclopropane complex [S. Maity et al., J. Chem. Phys. 145, 164304 (2016)]. The experimental and calculated D₀(S₀) values of the cyclohexane and cyclopentane complexes are practically identical, although the polarizability of cyclohexane is ∼20% larger than that of cyclopentane. Investigation of the calculated pairwise atomic contributions to the D2 dispersion energy reveals that this is due to subtle details of the binding geometries of the cycloalkanes relative to the 1-naphthol ring. The B97-D3 DFT method predicts dissociation energies within about ±1% of experiment, including the cyclopropane face complex. The B3LYP-D3 and ωB97X-D calculated dissociation energies are 7-9 and 13-20% higher than the experimental D₀(S₀) values. Without dispersion correction, all the complexes are calculated to be unbound.