Controlling of Photophysical Behavior of Rhenium(I) Complexes with 2,6-Di(thiazol-2-yl)pyridine-Based Ligands by Pendant pi-Conjugated Aryl Groups

The structure-property correlations and control of electronic excited states in transition metal complexes (TMCs) are of high significance for TMC-based functional material development. Within these studies, a series of Re(I) carbonyl complexes with aryl-substituted 2,6-di(thiazol-2-yl)pyridines (Ar-n-dtpy) was synthesized, and their ground- and excited-state properties were investigated. A number of condensed aromatic rings, which function as the linking mode of the aryl substituent, play a fundamental role in controlling photophysics of the resulting [ReCl(CO)(3)(Ar-n-dtpy-kappa N-2)]. Photoexcitation of [ReCl(CO)(3)(Ar-n-dtpy-kappa N-2)] with 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl leads to the population of (MLCT)-M-3. The lowest triplet state of Re(I) chromophores bearing 9-anthryl, 2-anthryl, 1-pyrenyl groups is ligand localized. The rhenium(I) complex with appended 1-pyrenyl group features long-lived room temperature emission attributed to the equilibrium between (MLCT)-M-3 and (IL)-I-3/(ILCT)-I-3. The excited-state dynamics in complexes [ReCl(CO)(3)(9-anthryl-dtpy-kappa N-2)] and [ReCl(CO)(3)(2-anthryl-dtpy-kappa N-2)] is strongly dependent on the electronic coupling between anthracene and {ReCl(CO)(3)(dtpy-kappa N-2)}. Less steric hindrance between the chromophores in [ReCl(CO)(3)(2-anthryl-dtpy-kappa N-2)] is responsible for the faster formation of (IL)-I-3/(ILCT)-I-3 and larger contribution of (ILCTanthracene -> dtpy)-I-3 in relation to the isomeric complex [ReCl(CO)(3)(9-anthryl-dtpy-kappa N-2)]. In agreement with stronger electronic communication between the aryl and Re(I) coordination centre, [ReCl(CO)(3)(2-anthryl-dtpy-kappa N-2)] displays room-temperature emission contributed to by (MLCT)-M-3 and (ILanthracene)-I-3/(ILCTanthracene -> dtpy)-I-3 phosphorescence. The latter presents rarely observed phenomena in luminescent metal complexes.