Tuning the Luminescence and Electroluminescence of Diphenylboron Complexes of 5-Substituted 2-(2‘-Pyridyl)indoles

Abstract

To examine the effect of substituent groups on the luminescence of BPh2(X-2-PI) complexes, three new air-stable boron complexes BPh2(F-2-PI) (5a), BPh2(Cl-2-PI) (5b), and BPh2(CH3O-2-PI) (5c) were synthesized and characterized, where F-2-PI = 5-fluoro-2-(2‘-pyridyl)indole, Cl-2-PI = 5-chloro-2-(2‘-pyridyl)indole, and CH3O-2-PI = 5-methoxyl-2-(2‘-pyridyl)indole. In these complexes, the 5-substituted 2-PI ligand chelates in a tretrahedral fashion to the boron center. Compounds 5a−c are luminescent, with 5a having the highest emission efficiency. Compared with the emission maximum of BPh2(2-PI) (516 nm), the emission maximum of 5a and 5b is blue-shifted to 490 and 487 nm, respectively, while the emission of 5c is red-shifted to 532 nm, indicating the possibility of tuning the luminescence of these complexes by varying the substituent groups on the 2-PI ligand. An electroluminescent device using compound 5a as the emitter and the electron transport material has been fabricated.