Influence of structural changes on photophysical properties of terpyridine derivates: Experimental studies and theoretical calculations

Four terpyridine ligands containing different aryl substituents 4'-(4-quinolinyl)-3,2':6′,3″-terpyridine (3-qtpy), 4'-(4-quinolinyl)-2,2':6′,2″-terpyridine (2-qtpy), 4'-(3-methyl-2-thienyl)-4,2':6′,4″-terpyridine (4-stpy) and 4'-(3-methyl-2-thienyl)-2,2':6′,2″-terpyridine (2-stpy) were synthesized in a one-pot procedure and characterized by elemental analysis, FT-IR and 1H- and 13C NMR spectroscopy. Additionally, the 2-stpy structure was confirmed by single crystal X-ray diffraction analysis. The influence of the N-position in the tpy and aryl substituents on the photophysical properties was systematically investigated by spectroscopic methods and simulated by density functional theory (DFT and TD-DFT) calculations. Thermal stability was observed until about 280 °C, making these kind of ligands interesting candidates for their use as complex ligands, which are obtained by solvothermal synthesis under temperatures of about 180 °C. The electrochemical behavior was also investigated. All molecules show irreversible anodic and cathodic voltammetric peaks in organic medium.