Acta Chimica Sinica ›› 2019, Vol. 77 ›› Issue (11): 1194-1202.DOI: 10.6023/A19080306 Previous Articles     Next Articles



刘笑静, 贾彦荣, 江豪, 高贯雷, 夏敏*()   

  1. 浙江理工大学生态染整技术教育部工程研究中心 杭州 310018
  • 投稿日期:2019-08-19 发布日期:2019-10-22
  • 通讯作者: 夏敏
  • 基金资助:

Two Polymorphs of Triphenylamine-substituted Benzo[d]imidazole: Mechanoluminescence with Different Colors and Mechanofluorochromism with Emission Shifts in Opposite Direction

Liu Xiaojing, Jia Yanrong, Jiang Hao, Gao Guanlei, Xia Min*()   

  1. Engineering Research Center for Eco-dyeing and Finishing Technology of Textiles, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018
  • Received:2019-08-19 Published:2019-10-22
  • Contact: Xia Min

Mechanofluorochromism (MFC) and mechanoluminescence (ML) are two types of significant solid-state optical phenomena which are closely dependent on conformations, packing modes and intermolecular interactions. Herein, through a three-step route involving aromatic nucleophilic substitution, reduction and oxidative cyclization in DMSO under air, a benzo[d]imidazole with triphenylamine and 4-cyanophenyl respectively located at C(2)- and N(1)-position is obtained in good yields. Two polymorphs TBIMB and TBIMG of 4-(2-(4-(diphenylamino)phenyl)-1H-benzo[d]imidazol-1-yl)benzonitrile (TBIM) corespondingly exhibit intense deep-blue (435 nm) and green fluorescence (505 nm). Under force stimuli, both polymorphs turn into amorphous phase with cyan fluorescence (457 nm). By fuming in solvent vapor or annealing treatment, only the ground TBIMB sample can be completely restored into the original crystalline structure, the ground TBIMG sample is just transformed into TBIMBcrystal. It is assumed that the enhanced energy barrier induced by the denser packing in TBIMG crystal makes the conversion from in amorphous phase to crystalline one kinetically infeasible. The crystallography reveals that triphenylamine moiety in TBIMG crystal is less restrained by intermolecular interactions than that in TBIMB crystal, which results in the long-wavelength TICT emission in the former crystal and the short-wavelength LE emission in the latter one. In exposure to force stimuli, TBIMB and TBIMG crystals respectively give out the blue (432 nm) and green (500 nm) flash. It is revealed by crystallography that both polymorphs hold centrosymmetric space groups. DFT calculations based on the molecular couples with strong intermolecular interactions demonstrate that the close-to-zero net dipole moments occurs on these couples. Hence, neither piezoelectric effect nor excitation of molecules on cracked surfaces by discharges between molecular couples should account for the ML behaviors of these two polymorphs. Due to the readily force-induced cleavage of the two crystals by particular chain-shaped packing, the endogenous friction discharge caused by relative movements between cleavage planes would excite molecules on these planes, and this mechanism is assumed to be mainly responsible for the ML activity of the two crystals.

Key words: mechanofluorochromism, mechanoluminescence, polymorphs, endogenous friction discharge, benzimidazole