Strategy to enhance solid-state fluorescence and aggregation-induced emission enhancement effect in pyrimidine boron complexes

Abstract

The synthesis and the solution/solid-state fluorescence properties of pyrimidine-based monoboron complexes differing in terms of the substituents [either two fluorine atoms (BF₂ complex) or two phenyl groups (BPh₂ complex)] on the boron atom are reported herein. Unrestricted C–Ar intramolecular rotation in the non-, trifluoromethyl-, and cyano-substituted derivatives resulted in negligible fluorescence in solution. On the other hand, methoxy- and dimethylamino-substituted analogues caused the restriction of the C–Ar intramolecular rotation and consequently resulted in relatively strong fluorescence in solution. The non-, trifluoromethyl-, and cyano-substituted derivatives showed a pronounced aggregation-induced emission enhancement effect. Dimethylamino-substituted derivatives exhibited solvatochromism in the fluorescence spectra. Substitution with BPh₂ effectively enhanced the fluorescence quantum yield compared to the corresponding BF₂ complexes in the solid-state.