Cyanoacetic acid tethered thiophene for well-matched LUMO level in Ru(II)-terpyridine dye sensitized solar cells

We synthesized two new terpyridine based Ru sensitizers (SY-01 and SY-02) with the lowest unoccupied molecular orbital (LUMO) levels of these two dyes are well-matched with that of the black dye (N749). Both sensitizers capable of exhibiting metal-to-ligand charge transfer band show a higher molar extinction coefficients (ε ∼ 5.0–6.8 × 103 M−1 cm−1) than that (4.2 × 103 M−1 cm−1) of N749 because of the enhanced absorption arising from thiophene moiety. Density functional theory calculations reveal that LUMOs of SY-01 and SY-02 are distributed over the terpyridine and thienyl moieties. The excited-state oxidation potentials, E°ox*, obtained by the electrochemical studies, range from −0.98 to −0.96 V, are sufficiently more negative than the conduction band edge of the TiO2 electrode (ca.−0.5 V). The increased conjugation conferred to SY-01 and SY-02 dyes through π-expansion by thiophene moiety increases light-harvesting and energy conversion efficiency in comparison with N749.