Self-assembling and piezofluorochromic properties of tert-butylcarbazole-based Schiff bases and the difluoroboron complex

Abstract

New tert-butylcarbazole-based Schiff bases TPMP and TPMA, as well as the difluoroboron complex of salicylaldimine TPOB were synthesized. It was found that TPMP and TPMA without any traditional gelation group could form organogels in toluene and o-dichlorobenzene, etc., stimulated by ultrasound. It was suggested that the planar π-skeletons and the large steric effect of tert-butyl groups would lead to appropriate π-π interaction to induce the gel formation. Interestingly, the nanofibers formed from salicylaldimine derivative TPMP could emit strong yellowish green light under UV irradiation. It should be noted that the difluoroboron complex of TPOB with non-planar aromatic unit could not gelate the selected solvents on account of the weak π-π interaction. However, it showed reversible piezofluorochromism. The as-prepared crystal of TPOB emitted strong yellow light and could be transformed into the powders emitting orange red light after grinding, and the fluorescence could recover when the ground powders were heated. Such reversible changes of the emitting colors for TPOB by the treatment of grinding and heating was resulted from the transformation between crystalline and amorphous states. Herein, we provided the strategy for fabricating new nontraditional π-gels directed by appropriate π-π interaction and new piezofluorochromic dyes via the introduction of non-planar π-skeletons.