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-κ 2 N)]. The molecular formulas of Re(I) compounds were confirmed by 1 H and 13 C 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-κ 2 N)]. 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.