Synthesis, characterisation, electrochemical study and photovoltaic measurements of a new terpyridine and pyridine-quinoline based mixed chelate ruthenium dye

Abstract

A novel ruthenium-terpyridine based photosensitizer, Ru[(p-F-tpy)(pcqH)Cl] PF6 (1); (p-F-tpy=4′-(4-fluorophenyl)-2,2′:6′,2″-terpyridine, pcqH=2-(2-pyridyl)-4-carboxyquinoline) was synthesized and spectroscopically characterized. The electronic spectrum of the complex shows the lowest energy MLCT band at 536nm in DMSO. The ground state pKa values of the acidic ligand (pcqH) and the Ru complex were spectrophotometrically determined. The pKa of the COOH group in the free ligand is 3.56, and this reduces to 2.89 when bound to the metal. The cyclic voltammetry of the complex shows a reversible RuII/III oxidation at 0.825V with respect to Ag/AgCl reference electrodes in DMF. The Cl group is very labile, substitution of the Cl group by H2O generates aqua species, which has been shown spectrophotometrically. A Pourbaix diagram for the Ru-aqua species has been constructed to show the detailed redox properties of the complex by means of cyclic voltammetry and differential pulse voltammetry at variable pH. Non-linear regression analysis was performed to generate the pKa values for the Ru-aqua species as 11.89 (RuII) and 4.00 (RuIII). Photovoltaic measurements with the dye were performed after anchoring onto a TiO2 surface with the I−/I3− redox electrolyte. Photovoltaic properties, like open-circuit photo-voltage (Voc=−0.35V), short-circuit photocurrent density (Jsc=1.428×10−4ampcm−2), fill factor (ff=39.4%) and solar-to-electric conversion efficiencies (η=0.13%), of the DSSCs constructed from the [Ru(p-F-tpy)(pcqH)Cl]PF6 sensitized TiO2 electrodes were measured. A DFT and TDDFT study has been performed on the complex. The TDDFT calculated absorption spectrum nicely matches the experimental spectrum.