Luminescent tetrahydrodibenzo[a,i]phenanthridin-5-yl)phenol-boron complexes (borophenanthridines)

Abstract

A series of weakly emissive, exited state intramolecular proton transfer active tetrahydrodibenzo[a,i]phenanthridin-5-yl)phenols were efficiently synthesized using 2-tetralone and substituted salicylaldehydes. These dyes were smoothly coordinated with boron trifluoride diethyletherate resulting in π-conjugated and rigid tetracoordinated boron-phenanthridine complexes. The complexes were highly emissive in solution and solid states with large Stokes shift values ranging from 6190 to 10410 cm−1 and moderate fluorescence quantum yields. A systematic photophysical and solvatochromism studies revealed that the intramolecular charge transfer process was more effective in borophenanthridines than with others, which was supported by DFT study. Further, the electrochemical studies testified the high electron-accepting ability of these boron complexes.