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

A novel ruthenium-terpyridine based photosensitizer, Ru[( p -F-tpy)(pcqH)Cl] PF 6 ( 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 536 nm in DMSO. The ground state pK a values of the acidic ligand (pcqH) and the Ru complex were spectrophotometrically determined. The pK a 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 Ru II/III oxidation at 0.825 V with respect to Ag/AgCl reference electrodes in DMF. The Cl group is very labile, substitution of the Cl group by H 2 O 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 pK a values for the Ru-aqua species as 11.89 (Ru II ) and 4.00 (Ru III ). Photovoltaic measurements with the dye were performed after anchoring onto a TiO 2 surface with the I − / I 3 − redox electrolyte. Photovoltaic properties, like open-circuit photo-voltage (Voc = −0.35 V), short-circuit photocurrent density ( J sc = 1.428 × 10 −4 amp cm −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]PF 6 sensitized TiO 2 electrodes were measured. A DFT and TDDFT study has been performed on the complex. The TDDFT calculated absorption spectrum nicely matches the experimental spectrum. [ABSTRACT FROM AUTHOR]