Kankatala S. V. Gupta

Thiocyanate-free cyclometalated ruthenium(II) sensitizers for DSSC: A combined experimental and theoretical investigation

In an effort to bring out efficient thiocyanate-free dyes for dye sensitized solar cells (DSSC) we have designed, synthesized and characterized four novel cyclometalated ruthenium(II) dyes (M1 to M4) with superior photochemical properties. All dyes contain terpyridyl ligands (TPY) with carboxylic acids as anchoring groups and cyclometalated ligand (TPY-C) with substituents for fine tuning the electronic properties. We obtain a broad absorption band which extends up to 725 nm due to metal to ligand charge transfer (MLCT) when donating groups are used, which slightly blue-shifts when a withdrawing group is used. In addition to the CT, small HOMO-LUMO gaps are obtained from electrochemical measurements which indicate characteristics of an ideal sensitizer. All four dyes were used as sensitizers for DSSC and photoelectrochemical measurements were carried out. Reasonably good efficiency (7.1%) has been achieved for . We have carried out periodic-DFT studies of these dyes adsorbed on the (TiO2)38 cluster. They revealed that, in bidentate bridging mode the dyes preferably bind with the help of two carboxylic groups onto the TiO2. To the best of our knowledge we are the first to do DFT studies of thiocyanate free cyclometalated ruthenium(ii) dyes tethered to TiO2.

2,6-Bis(1-methylbenzimidazol-2-yl)pyridine: A New Ancillary Ligand for Efficient Thiocyanate-Free Ruthenium Sensitizer in Dye- Sensitized Solar Cell Applications

We have designed and synthesized a new thiocyante-free ruthenium complex containing 2,6-bis(1-methylbenzimidazol-2-yl)pyridine, coded as SPS-G3, and it has been used as an efficient photosensitizer for dye-sensitized solar cells (DSSCs). Upon sensitization of SPS-G3 on nanocrystalline TiO2 film, the DSSC test cell yielded a large short-circuit photocurrent (16.15 mA cm(-2)), an open circuit voltage of 0.52 V, and a fill factor (FF) of 0.72, resulting in an overall power conversion efficiency (PCE) of 6.04% under simulated AM 1.5 solar irradiation (100 mW cm(-2)). DSSCs were prepared by adding various concentrations of multiwall carbon nanotubes (MWCNTs) (up to 0.5 wt %) into the TiO2 nanoparticles. Optimization of MWCNT concentration (0.3 wt %) lead to PCE values as high as 7.76%, while the test cells employing pure TiO2 photoanode obtained an efficiency of 6.04%. The results indicate that the PCE of MWCNTs/TiO2 composite DSSCs are dependent on the quantity of MWCNTs loading on the photoanodes. A small amount (0.3 wt %) clearly enhances the PCE of DSSC, while the excessive MWCNT loading lowers the photovoltaic performance of the DSSC. The increase in the PCE has been attributed to the decrease in charge-transport resistance, charge-transport time, and electron lifetime, which are estimated from electrochemical impedance spectra.

Copper-catalyzed regio and diastereoselective three component C–N, C–C and C–O bond forming reaction: oxidative sp3 C–H functionalization

A highly regio and diastereoselective copper catalyzed three component reaction of tetrahydroisoquinolines (THIQs), aldehydes, and naphthols to furnish naphthoxazine derivatives under mild conditions was developed. The initial generation of iminium ions followed by the nucleophilic attack of naphthol presumed to deliver 15-phenyl-7a,12,13,15-tetrahydronaphtho[1′,2′:5,6][1,3]oxazino[2,3-a]isoquinoline derivatives. The reaction ensured the formation of C–C, C–N and C–O bonds in a one-pot reaction to produce ring fused N,O-acetals in good yields. The three component reaction, the inexpensive copper catalyst in the absence of a co-oxidant/additive and the direct regioselective oxidative sp3 C–H functionalization are the attractive features of this approach. The preliminary photophysical properties obtained for selected compounds were presented.

A New Heteroleptic Biquinoline Ruthenium(II) Sensitizer for Near-IR Sensitization of Nanocrystalline TiO2

Ruthenium(II) complex containing cis-[Ru(H2dcbiq)(L)(NCS)2], where H2dcbiq = 4,4′-dicarboxy-2,2′-biquinoline and L = 4,4′-di-tert-butyl-2-2′-dipyridyl coded as SPS-02, was synthesized and fully characterized. This complex showed appreciably broad absorption range. The new complex was used as photosensitizer in nanocrystalline TiO2 dye-sensitized solar cell application. cis-[Ru(H2dcbiq)(L)(NCS)2] (SPS-02) achieved efficient sensitization of nanocrystalline TiO2 over the whole visible range, extending into the near-IR region (ca. 1000 nm) with superior short-circuit photocurrent density ( = 9.13 mA cm−2) and conversion efficiency (η = 2.09%) compared with complex cis-[Ru(H2dcbiq)2(NCS)2] (1) under an irradiation of full sunlight (100 mW cm−2).