Interactions between haloperfluorobenzenes and fluoranthene in luminescent cocrystals from π-hole⋯π to σ-hole⋯π bonds

Abstract

Although there are a number of literature reports in the field of crystal design by σ-hole⋯π or π-hole⋯π bond, there are still very few discussions about under what conditions it is easier to form a σ-hole⋯π bond and under what conditions it is easier to form a π-hole⋯π bond. In order to explore this issue, nine cocrystals were assembled using haloperfluorobenzenes (Cl, Br, I) as the σ-/π-hole bonding donors with fluoranthene (FA) as the bonding acceptor. Single-crystal X-ray diffraction (XRD) analysis reveals that a π-hole⋯π bond occurred in all cocrystals, while both σ-hole⋯π and π-hole⋯π bonds existed in 14DIPB/135TIPB/12DIPB–FA cocrystals. The main bonding patterns of the cocrystals change from π-hole⋯π to additional σ-hole⋯π bonds in the order of the halogen atoms Cl and Br to I. Besides, based on the computational chemistry and the XRD analysis, it is proposed that it is very likely that cocrystals are assembled by both σ-hole⋯π and π-hole⋯π bonding when the σ-hole MEP is much more positive than the π-hole MEP by about 65 kJ mol⁻¹, and by π-hole⋯π bonding when the MEP of the σ-hole is comparable with that of the π-hole. In addition, the geometric factor in terms of both ring thickness and diameter may play an important part in affecting the bonding pattern. Finally, due to the different interaction patterns and heavy atom perturbing sources, FA in the cocrystals displays different luminescent behaviors.