Synthesis of tautomerization-inhibited diamino substituted tetraphenylethene derivatives with different mechanochromisms: the vital role of chlorine

Abstract

The stereochemistry of tetraphenylethene (TPE) derivatives with aggregation induced emission (AIE) characteristics has demonstrated significant value in advanced materials and life sciences. Geometric Z/E-diamino substituted TPE (Z/E-2NH₂-TPE) suffers from tautomerization and separation. To resolve this problem, pure geometric Z/E diamino and dichloro dual-substituted TPE (Z/E-2Cl-2NH₂-TPE) molecules were designed precisely and separated via common column chromatography by introducing chlorine. Tautomerization would not occur even after being kept at increased temperature (200 °C) for 2 hours or at room temperature for 6 months. The role of chlorine atoms in geometric Z/E-2Cl-2NH₂-TPE molecules has been deeply elucidated through theoretical computational chemistry methods and intermolecular interaction. Compared with Z/E-2NH₂-TPE molecules, the Frank–Condon excitation, transition state of the tautomerization process, conical intersection, and photoluminescence in the potential energy surface of Z/E-2Cl-2NH₂-TPE molecules were similar to those of Z/E-2NH₂-TPE molecules. The energy barrier of tautomerization seldom clarified the role of the chlorine atoms while enhanced intermolecular interaction provided by chlorine atoms effectively rigidified the conformation of the tautomerization process. Thereafter, different mechanochromism (MC) photochemical properties were probed in depth, which were induced by structure-dependent molecules’ H/J-aggregation state and reorganization energy. The tautomerization-inhibited Z/E-2Cl-2NH₂-TPE molecules with a reactive functional group provided a good template for designing advanced materials.