Controlling of Photophysical Behavior of Rhenium(I) Complexes with 2,6-Di(thiazol-2-yl)pyridine-Based Ligands by Pendant π-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-κ(2)N)]. Photoexcitation of [ReCl(CO)(3)(Ar(n)-dtpy-κ(2)N)] with 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl leads to the population of (3)MLCT. 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 (3)MLCT and (3)IL/(3)ILCT. The excited-state dynamics in complexes [ReCl(CO)(3)(9-anthryl-dtpy-κ(2)N)] and [ReCl(CO)(3)(2-anthryl-dtpy-κ(2)N)] is strongly dependent on the electronic coupling between anthracene and {ReCl(CO)(3)(dtpy-κ(2)N)}. Less steric hindrance between the chromophores in [ReCl(CO)(3)(2-anthryl-dtpy-κ(2)N)] is responsible for the faster formation of (3)IL/(3)ILCT and larger contribution of (3)ILCT(anthracene)(→)(dtpy) in relation to the isomeric complex [ReCl(CO)(3)(9-anthryl-dtpy-κ(2)N)]. In agreement with stronger electronic communication between the aryl and Re(I) coordination centre, [ReCl(CO)(3)(2-anthryl-dtpy-κ(2)N)] displays room-temperature emission contributed to by (3)MLCT and (3)IL(anthracene)/(3)ILCT(anthracene)(→)(dtpy) phosphorescence. The latter presents rarely observed phenomena in luminescent metal complexes.