Effects of Methyl-Substituted Phenanthrolines on the Performance of Ruthenium(II) Dye-Sensitizers

ACS Appl. Mater. Interfaces

Oliveira

Meyer

et al. 2019

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A series of cis-[Ru(LL)(dcbH2)(NCS)2] compounds, where dcbH2 = 2,2′-bipyridine-4,4′-dicarboxylic acid and LL = 1,10-phenanthroline (Ru(phen)), 4,7-dipyrrole-1,10-phenanthroline (Ru(pyr)), 4,7-diindole-1,10-phenanthroline (Ru(ind)), or 4,7-dicarbazole-1,10-phenanthroline (Ru(cbz)), was investigated for application as sensitizers in mesoporous TiO2 dye-sensitized solar cells (DSSCs). A systematic increase in the number of rings of the aromatic substituents at the 4,7-positions of the 1,10-phenanthroline allowed tuning of the molecular size of the sensitizers and the energy stored in the excited state while maintaining the same ground-state Ru3+/2+ reduction potentials. These small structural changes had a significant influence on the rates and/or efficiencies of electron injection, back-electron transfer, recombination to oxidized mediators, lateral self-exchange electron transfer, and regeneration through iodide oxidation that were reflected in distinct photoelectrochemical performance of full operating DSSCs. The global efficiencies, open-circuit voltages, and short-circuit current densities of the DSSCs consistently followed the trend Ru(pyr) < Ru(ind) < Ru(phen) < Ru(cbz), and the most optimal performance of Ru(cbz) was ascribed to dramatically slower recombination to the oxidized redox mediators. Transient photovoltage and transient absorption experiments both revealed significantly slower recombination as the size of the aromatic substituents increased with Ru(cbz) providing the most promising behavior for application in dye sensitization.

Section: Resultsmentioning

confidence: 77%

Inhibiting Charge Recombination in cis-Ru(NCS)₂ Diimine Sensitizers with Aromatic Substituents

ACS Appl. Mater. Interfaces

Oliveira

Meyer

et al. 2019

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“…The materials and reagents were used as received from the indicated commercial suppliers: N , N -dimethylformamide (DMF; Vetec, ≥99.8%), [Ru( p -cymene)Cl 2 ] 2 (Strem, 98%), 1,10-phenanthroline (phen; Strem, 99%), 4,7-dimethyl-1,10-phenanthroline (Me 2 -phen; Alfa Aesar, 98%), 4,7-diphenyl-1,10-phenanthroline (Ph 2 -phen; Vetec, 99%), 4,7-dimethoxy-1,10-phenanthroline ((MeO) 2 -phen; Aldrich, 97%), 4,7-dichloro-1,10-phenanthroline (eNovation, 97%), sodium thiocyanate (NaNCS; Merck, 98.5%), methanolic solution of tetra- n -butylammonium hydroxide (TBAOH; Sigma-Aldrich, 1.0 mol L –1 ), methanol (Synth, 99.8%), Sephadex LH-20 (Aldrich), acetonitrile (Merck, Lichrosolv), and trifluoracetic acid (TFA; Vetec, 99.8%, UV-HPLC). 2,2′-Bipyridine-4,4′-dicarboxylic acid (dcbH 2 ), cis -[Ru(R-phen)(dcbH 2 )Cl 2 ], and cis -[Ru(R-phen)(dcbH 2 )(NCS) 2 ] (R = H, Me and Ph) were available from previous studies. , …”

Section: Methodsmentioning

confidence: 99%

“…2,2′-Bipyridine-4,4′-dicarboxylic acid (dcbH 2 ), cis-[Ru(R-phen)(dcbH 2 )Cl 2 ], and cis-[Ru(R-phen)-(dcbH 2 )(NCS) 2 ] (R = H, Me and Ph) were available from previous studies. 4,23 Methods. Electronic absorption spectra were recorded from 190 to 1100 nm in quartz cuvettes (1.000 cm path length) using an Agilent 8453 diode-array spectrophotometer.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Mechanistic Insights into the Stepwise Assembly of Ruthenium(II) Tris-heteroleptic Compounds

Polo

2018

Inorg. Chem.

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The ruthenium(II) tris-heteroleptic compounds cis-[Ru(NN)(dcbH2)(NCS)2], NN = polypyridyl ligand and dcbH2 = 2,2′-bipyridine-4,4′-dicarboxylic acid, can be synthesized by a one-pot route starting from [Ru(p-cymene)Cl2]2, followed by the sequential addition of ligands. In this work, each synthetic step for the cis-[Ru(R-phen)(dcbH2)(NCS)2] (R = H, Me, Ph, MeO, or Cl) preparation was individually investigated, aiming to identify reaction intermediates and to establish correlations among temperature, reaction time, reactant concentration, and the identity of the substituent of the polypyridyl ligand with the kinetics of the reactions and distribution of the products. The first step is the cleavage of [Ru(p-cymene)Cl2]2, followed by the coordination of R-phen via an associative mechanism and establishment of a direct correlation between the electron-donating or electron-withdrawing character of R and the reaction rates. The second step is the conversion of [Ru(R-phen)(p-cymene)Cl]Cl to cis-[Ru(R-phen)(dcbH2)Cl2], and the rate-determining step is the formation of the intermediate [Ru(R-phen)Cl2], which exhibits a low dependence on R. The last step is the substitution of Cl– by NCS–, and the N-bound isomer is the major product. The reaction temperature, time, and identity of R influence the relative distribution of the linkage isomers. The comprehension of each of these processes is a key factor to develop new strategies to optimize the one-pot synthetic route.

“…All sensitizers investigated were available from previous studies. 6,7 Preparation. Transparent mesoporous nanocrystalline TiO 2 thin films were prepared as previously described in the literature.…”

Section: ■ Introductionmentioning

confidence: 99%

Correlation Between Charge Recombination and Lateral Hole-Hopping Kinetics in a Series of cis-Ru(phen′)(dcb)(NCS)₂ Dye-Sensitized Solar Cells

Sampaio

ACS Appl. Mater. Interfaces

Polo

et al. 2017

Self Cite

Four complexes of the general form cis-Ru(phen')(dcb)(NCS), where dcb is 4,4'-(COH)-2,2'-bipyridine and phen' is 1,10-phenanthroline (phen), 4,7-(CH)-phen (Ph-phen), 4,7-(CH)-phen (Me-phen), or 3,4,7,8-(CH)-phen (Me-phen), were anchored to mesoporous TiO thin films for applications as sensitizers in dye-sensitized solar cells (DSSCs). The compounds displayed metal based reductions E(Ru) = 1.01 ± 0.05 V vs NHE and were potent reductants competent of excited-state electron transfer to TiO with yields ϕ ≥ 0.75 in acetonitrile electrolytes. Average charge recombination rate constants, k, abstracted from nanosecond transient absorption measurements, and the apparent diffusion coefficients for lateral hole-hopping, abstracted from chronabsorptometry measurements, showed the same sensitizer dependency: Ru(Me-phen) > Ru(Ph-phen) > Ru(Me-phen) ≈ Ru(phen). When used in operational solar cells, Ru(Ph-phen) was most optimal with an efficiency of (6.6 ± 0.5)% in ionic liquids under 1 sun illumination. The superior performance of Ru(Ph-phen) was traced to a higher injection yield and more efficient regeneration due to an unusually small sensitivity of k to the number of injected electrons.