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Effect of geometry factor on the priority of σ-hole···π and π-hole···π bond in phosphorescent cocrystals by pyrene or phenanthrene and trihaloperfluorobenzenes

Abstract

Introducing heavy atom perturbers such as iodine and bromine by σ–hole⋯π or π–hole⋯π bonds to 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 π–electron system. The bonding donors used usually such as halo– or multihaloperfluorobenzenes possess both σ–hole and π–hole. One question is that under what condition do σ–hole or π–hole bonding, or both occur? It is proposed that in some cases geometry of bonding donors should be one of key factors besides the difference of molecular surface electrostatic potential (SEP) of σ–hole and π–hole, and interaction energy in influencing bonding patterns in cocrystals. That is, thicker multi-haloperfluorobenzene due to larger halogen atom radius is not beneficial to π–hole⋯π bond. While multi-haloperfluorobenzene due to larger size can reach vertically adjacent π-system in a π–hole⋯π bonding pair to produce of typical above-plane σ–hole⋯π bond, or directly produce of σ–hole⋯π bond without π–hole⋯π bond as SEP of σ–hole is 65 kJ mol-1 higher than π–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 very typical σ–hole⋯π bonding in Pyr–TIPB (1) and Phe–TIPB (3) has priority over π–hole⋯π bond and other interaction because larger size and thicker TIPB, while π–hole⋯π bonding in Pyr–TBrPB (2) and Phe–TBrPB (4) has priority over σ–hole⋯π bond and other interaction because smaller size and thinner TBrPB. Moreover, red phosphorescence of pyrene in cocrystal Pyr–TIPB assembled by halogen bonding was taken firstly under UV-365 at room temperature because of typical above–plane C-I⋯π bond.

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Publication details

The article was received on 21 Nov 2017, accepted on 05 Jan 2018 and first published on 08 Jan 2018


Article type: Paper
DOI: 10.1039/C7NJ04536K
Citation: New J. Chem., 2018, Accepted Manuscript
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    Effect of geometry factor on the priority of σ-hole···π and π-hole···π bond in phosphorescent cocrystals by pyrene or phenanthrene and trihaloperfluorobenzenes

    L. L. Li, W. X. Wu, Z. F. Liu and W. J. Jin, New J. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C7NJ04536K

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