Difluoroboron Complexes of Aromatic Imidazole-Functionalized 2-(Benzo[D]Thiazol-2-Yl)Phenol (BTZ): Synthesis and Luminescence Properties

Abstract

Two aromatic imidazole-functionalized ligands (BTZ-PI-OH and BTZ-IM-OH) and their difluoroboron complexes (BTZ-PI-BF2 and BTZ-IM-BF2) were successfully synthesized by linking the aromatic imidazole units into 2-(benzo[d]thiazol-2-yl)phenol (BTZ-OH) via Suzuki-Miyaura cross-coupling reaction, and characterized by NMR (1H and 13C), HR-MS and FT-IR spectra. The photophysical, electrochemical properties and thermal stability of the ligands and the difluoroboron complexes were systematically investigated by experimental and theoretical methods to reveal their relationship between the molecular structures and photoelectric properties. The ligands exhibited dual fluorescence (enol emission and keto emission) due to the characteristics of excited-state intramolecular proton-transfer (ESIPT) in solution, while they showed only one emission in solid thin films. Compared with the ligands, the difluoroboron complexes showed a significant blue-shifted and enhanced emission due to the restricted conformation change. The solution-processed doped devices using the difluoroboron complexes as the emitting materials exhibited green-blue emission with maximum external quantum efficiency (EQEmax) of 1.35% for BTZ-PI-BF2 and 3.08% for BTZ-IM-BF2, respectively.

Keywords: Difluoroboron complex, 2-(Benzo[d]thiazol-2-yl)phenol ligand, Aromatic imidazole, Photophysical property, Electroluminescence