Synthesis and Characteristics of Novel Trager's Bases with the Properties of Aggregation-Induced Emission

A-shaped geometry configuration of Troger's base (TB) is theoretically disadvantages to form pi-pi close stacking, which commonly results in fluorescence quenching in the solid state. A number of A-shaped cyano styrene based on Troger's base (compounds la, 2a, 3a and 4a) was firstly developed with the structure of D-pi-C-pi-D which exhibited a typical aggregation-induced emission (AIE) behavior via Knoevenagel reaction with high yield. The thiophene ring was successful introduced into the Troger's base skeleton firstly to obtain novel compound 5a with good solid luminescence via palladium-catalyzed Heck coupling reaction. The phenyl groups and thiophene ring were used as the electron donor and TB was used as a nucleus. All of these compounds were characterized and confirmed by H-1 NMR, C-13 NMR and MS spectra. All of the compounds were highly emissive in the condensed phase. In addition, compounds la, 2a, 3a and 4a were weakly fluorescent in solutions, but compound 5a exhibited blue emission strongly in solution, which revealed distinct aggregation-induced emission characteristics. The photo-physical properties of these compounds were studied in detail. We aimed at verifying the AIE properties of these compounds mainly. And the results showed a significant increase in fluorescence of these compounds with the addition of water, indicating that the synthesized compounds really have apparent AIE behavior. The solvent effect behavior was investigated to evaluate the effect of the solvent polarity on compounds la, 2a and 5a. Compound 2a showed some solvent effect, and all the emission peaks were red-shifted due to the increasing of the polarity of the solvents, indicating that a significant ICT effect existed in these compounds. In summary, in the process of the exploration of highly emissive organic solids, a new design strategy was presented and a new system of AIE materials was established. This study reveals that when constructing aggregation-induced emission molecules using substituent groups with expanded pi-conjugation and introduction of appropriate steric hindrance on the substituent groups can restrict the formation of excimers effectively, hence achieving efficient solid state emission, which are expected to be used in electroluminescent field with potential value.