The effect of 2-, 3- and 4-pyridyl substituents on photophysics of fac-[ReCl(CO)3(n-pytpy-κ2N)] complexes: Experimental and theoretical insights

Abstract

Three rhenium(I) carbonyl complexes with 4′-(n-pyridyl)−2,2′:6′,2′′- terpyridines (n-pytpy; n = 2, 3 and 4), coordinated to the central metal in a bidentate mode, have been synthesized in order to explore the impact of 2-, 3- and 4-pyridyl substituents on the thermal, photoluminescent, and electrochemical properties of the isomeric forms of fac-[ReCl(CO)3(n-pytpy-κ2N)]. The molecular formulas of Re(I) compounds were confirmed by 1H and 13C NMR and X-Ray analysis. Thermal properties were determined by differential scanning calorimetry. Electrochemical behaviour was investigated using cyclic voltammetry. The ground and excited state properties of 1–3 were investigated utilizing absorption and emission spectroscopy, and photoluminescence studies were performed both in solution and solid state, as a powder and thin films. In order to gain more insight into the electronic structure of the Re(I) complexes, the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed. Both experimental and theoretical studies indicated MLLCT nature of the emissive state in fac-[ReCl(CO)3(n-pytpy-κ2N)]. The differences in emissive behaviour of 1–3 were correlated with changes in electron-withdrawing properties of the pendant n-pyridyl incorporated into 2,2′:6′,2′′-terpyridine core and changes in the architecture of crystal packing. The ability of the complexes for light emission under external voltage was preliminary tested in devices with configuration ITO/PEDOT:PSS/complex/Al and ITO/PEDOT:PSS/PVK:PBD:complex/Al.