Effect of geometry factors on the priority of sigma-hole center dot center dot center dot pi and pi-hole center dot center dot center dot pi bond in phosphorescent cocrystals formed by pyrene or phenanthrene and trihaloperfluorobenzenes

摘要

Introducing heavy atom perturbers such as iodine and bromine with sigma-hole center dot center dot center dot pi or pi-hole center dot center dot center dot pi bonds into cocrystals is an effective way to induce phosphorescence in the design of new luminescent materials containing rigid and planar polycyclic aromatic hydrocarbons with large conjugated p-electron systems. The bonding donors usually used such as halo-or multihaloperfluorobenzenes possess both a s-hole and a p-hole. One question is under what condition do s-hole or p-hole bonding, or both, occur? It is proposed that in some cases the geometry of the bonding donors should be one of the key factors, besides the difference of molecular surface electrostatic potential (SEP) of the s-hole and p-hole, and the interaction energy, in influencing bonding patterns in cocrystals. That is, a thicker multihaloperfluorobenzene ring (caused by a larger halogen atom radius) is not beneficial to pi-hole center dot center dot center dot pi bonding. However, a multi-haloperfluorobenzene, due to its larger size, can reach the vertically adjacent p-system in a pi-hole center dot center dot center dot pi bonding pair to produce a typical above-plane sigma-hole center dot center dot center dot pi bond, or directly produce a sigma-hole center dot center dot center dot pi bond without a pi-hole center dot center dot center dot pi bond, as the SEP of a s-hole is 65 kJ mol(-1)1 higher than a p-hole. Therefore, four cocrystals of Pyr-TIPB (1), Pyr-TBrPB (2), Phe-TIPB (3) and Phe-TBrPB (4) were prepared. Single-crystal X-ray diffraction (XRD) analysis, computation of SEP and interaction energy reveal that the very typical sigma-hole center dot center dot center dot pi bonding in Pyr-TIPB (1) and Phe-TIPB (3) has priority over pi-hole center dot center dot center dot pi bonding and other interactions because of the larger size and thicker TIPB, while pi-hole center dot center dot center dot pi bonding in Pyr-TBrPB (2) and Phe-TBrPB (4) has priority over sigma-hole center dot center dot center dot pi bonding and other interactions because of the smaller and thinner TBrPB. Moreover, red phosphorescence of pyrene in cocrystalline Pyr-TIPB assembled by halogen bonding was observed for the first time under UV-365 at room temperature because of the typical above-plane C-I center dot center dot center dot pi bond.