Structure–Photoluminescence Quenching Relationships of Iridium(III)–Tris(phenylpyridine) Complexes

Abstract

AbstractThe synthesis, structural, photophysical, theoretical, and electrochemical characterization of four tris(2‐phenylpyridine)‐based IrIII complexes are reported. The complexes were functionalized on the pyridine or on the phenyl rings with amide moieties substituted with a tris(ethyl)amine or ethyl groups, thereby yielding a family of compounds with hemicaged or open (without a capping unit but with similar functional groups on the ligand) structure. Within the context of the parent tris(2‐phenylpyridine) and the full‐cage iridium(III) complexes, structure–photoluminescence quenching relationships (SPQR) of the four complexes have been investigated. Luminescence quenching by oxygen has been studied with Stern–Volmer plots and through evaluation of the thermodynamic parameters involved in the quenching process. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations have been performed on the complexes to gain insights into structural and electronicfeatures and the nature of the excited states involved in the electronic absorption processes. Interestingly, shielding by the capping unit of moieties in which the LUMO orbital is mostly localized (on the pyridines) results in a dramatic 40 % decrease in oxygen quenching. Conversely, shielding ofmoieties in which the HOMO orbital is partially localized (on the phenyl rings) does not induce any change in the oxygen quenching degree. In both sets of compounds, the thermodynamic feasibility of oxygen quenching is the same for the hemicaged and open compounds, thus giving evidence of the structural origin of such quenching decrease. The SPQRopens up new routes to the design of tailored, more or less sensitive to oxygen, luminescent iridium complexes (e.g., for use as biolabels).