Fine-Tuning of Photophysical and Electronic Properties of Materials for Photonic Devices Through Remote Functionalization

We report four new iridium(III) complexes of the type [Ir(ppy)2(N?N)][PF6] in which N?N is a 4,6-diphenyl-2,2'-bipyridine and the 4-phenyl ring is substituted at either the para or meta positions [4-Me, N?N = 1; 4-Br, N?N = 2; 3,5-Br2, N?N = 3; 3,5-(C6H4-4-NPh2)2, N?N = 4]. The complexes have been fully characterized, and single-crystal diffraction analyses of [Ir(ppy)2(N?N)][PF6] (N?N = 13) confirmed that each [Ir(ppy)2(N?N)]+ cation exhibits face-to-face p-stacking between the pendant phenyl substituent of the N?N ligand and the cyclometallated phenyl ring of an adjacent [ppy] ligand. In solution, the complexes are short-lived emitters; the emission maxima for [Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6], and [Ir(ppy)2(4)][PF6] are similar (?em = 600608 nm), but the presence of the two bromo substituents in [Ir(ppy)2(3)][PF6] produces a redshift of ca. 30 nm. The solid-state photoluminescent emission spectra of thin films of the complexes are similar to those in solution. The performances of the complexes as electroluminescent components in light-emitting electrochemical cells (LECs) have been evaluated. The electroluminescence spectra show slight blueshifts with repect to the photoluminscence bands. LEC turn-on times vary from instantaneous for N?N = 2 to 2 h for N?N = 1. The device data suggest that the incorporation of Br substituents into the N?N co-ligand may not be beneficial.