Halogen‐Containing TPA‐Based Luminogens: Different Molecular Packing and Different Mechanoluminescence

Abstract Organic mechanoluminescence (ML) materials have attracted much attention for their various application prospects in luminescent devices. However, the pace of their development has been greatly limited by the unclear inherent mechanism. Herein, halogen atoms are systematically introduced into ML for the first time to deeply explore the light‐emitting process and internal mechanism. Thus, a series of triphenylamine (TPA) derivatives is obtained with diverse ML properties, including TPA‐oF, TPA‐mF, TPA‐pF, TPA‐oCl, TPA‐mCl, TPA‐pCl, TPA‐oBr, TPA‐mBr, TPA‐pBr, and TPA‐ph. Among them, with the introduced chlorine and bromine atoms in the para‐position of the phenyl ring in TPA‐ph, the resultant TPA‐pCl and TPA‐pBr demonstrate bright ML; whereas the introduced fluorine atom in TPA‐pF drastically reduces the ML performance. Careful analysis of their optical properties and crystal structures coupled with theoretical calculations confirms that different halogen atoms in the TPA derivatives can really lead to diverse intermolecular interactions, and the strong intermolecular interactions are actually beneficial for the ML effect by reducing energy loss through nonradiative relaxation channels under a stimulus of mechanical force; however, unsatisfying ML performance is observed in the crystal with an overtight molecular packing, on account of the unbreakable crystals with high rigidity.