2‑(2′-Hydroxyphenyl)benzimidazole and 9,10-Phenanthroimidazole Chelates and Borate Complexes: Solution- and Solid-State Emitters

The synthesis, structural, and optical properties of a series of luminescent N-alkylated 2-(2′-hydroxyphenyl)benzimidazole (HBI) or N-arylated 9,10-phenanthroimidazole (HPI) borate complexes are described. The optical properties of these complexes as well as their corresponding ligands were evaluated in solution and the solid state. Efficient emission in the blue-green region was obtained with quantum yields up to 91% in CH2Cl2 and 27% in the solid state. These emissions originate from excited state intramolecular proton transfer (ESIPT) for the ligands and from a singlet excited state for the borate complexes.