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.