Controlling Photophysical Properties in Bis-Cyclometalated Ir(III)-Terpyridine Complexes through Photoinduced Intraligand Charge Transfer

This work is the study of the role of a remote amine substituent on the terpyridine ligand in controlling the photophysical and electroluminescent behavior of complexes [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆. Introduction of the amine group into the Ph-terpy framework induced perturbations in the absorption and luminescent characteristics of [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆ relative to the parent chromophores [Ir(Ph-btz)₂(terpy-κ²N)]PF₆ and [Ir(Ph-btz)₂(C₆H₅-terpy-κ²N)]PF₆. Consistent with the presence of vibronic structure, negligible emission solvatochromism, weak rigidochromic behavior, and substantial overlap with the phosphorescence of 2-phenylbenzothiazole, the emissive triplet excited state of the model complexes was assigned to ³IL_Ph-btz with a minor ³MLCT contribution. The amine-substituted Ir(III) complexes were found to exhibit altered emission characteristics, manifested by a structureless emission band impacted by the amine group and solvent polarity. It was rationalized by a switch from the ³IL_Ph-btz/MLCT excited state in model chromophores to a configurationally mixed ³ILCT/IL/MLCT_R-terpy in [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆. With respect to the preliminary electroluminescence investigations, it was found that the introduction of the triphenylamine moiety enhances the stability of O/PEDOT/PSS/complex/Al devices. A deep insight into ground- and excited-state characters and photophysical properties of [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆ was obtained by applying a wide range of experimental techniques, including cyclic voltammetry, UV–vis spectroscopy, photoluminescence spectroscopy, and transient absorption, complemented by DFT and TD-DFT calculations.