Variation of para Substituent on 2‐Phenol of Tetraaryl‐Substituted Imidazole‐Boron Difluoride Complexes: Synthesis, Characterization, and Photophysical Properties

Abstract

AbstractFive N,O‐chelated boron complexes (i.e., 3 a–3 e) were prepared by treating imidazole precursors with BF3⋅Et2O. These imidazole derivatives were prepared from an arylboronic acid and 4‐bromo‐2‐(1,4,5‐triphenyl‐1H‐imidazol‐2‐yl)phenol. X‐ray diffraction analysis of 3 a–3 c and 3 e revealed that the phenyl rings bonded to the imidazole are severely twisted, but the interplanar angle of the biphenyl group is approximately 24°. The complexes were characterized by UV/vis and fluorescence spectroscopy, cyclic voltammetry, and theoretical calculations. The complexes exhibited moderate quantum yields when excited at the absorption maximum, and their fluorescence and UV/vis absorption spectra show large Stokes shifts relative to those of boron‐dipyrromethene compounds. Notably, two emission bands were observed for 3 a–3 d in the solid state. Powder XRD analysis and solid‐state emission studies of as‐prepared, ground, and fumed samples were used to reveal the origin of this dual emission.