Publications (12)65.76 Total impact
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Article: Atomic Level Resolution of Dye Regeneration in the Dye Sensitized Solar Cell.
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ABSTRACT: Two donor-acceptor organic dyes have been synthesized that differ only by a two-heteroatom change from oxygen to sulfur within the donor unit. The two dyes, (E)-3-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid (Dye-O) and (E)-3-(5-(4-(bis(4-(hexylthio)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid) (Dye-S), were tested in solar cell devices employing both I3-/I- based and [Co(bpy)3]3+/2+ redox mediators. Power conversion efficiencies (PCE) over 6% under simulated AM 1.5 illumination (1 Sun) were achieved in both electrolytes. Despite similar optical and redox properties for the two dyes, a consistently higher open-circuit voltage (Voc) was measured for Dye-S relative to Dye-O. The improved efficiency observed with Dye-S in an iodide redox mediator is against the commonly held view that sulfur atoms promote charge recombination attributed to inner-sphere interactions Detailed mechanistic studies revealed that this is a consequence of a 25-fold enhancement of the regeneration rate constant that enhances the regeneration yield under open circuit conditions. The data shows that a high short circuit photocurrent does not imply optimal regeneration efficiency as is often assumed.Journal of the American Chemical Society 01/2013; · 9.91 Impact Factor -
Article: Ru complexes of thienyl-functionalized dipyrrins as NCS-free sensitizers for the dye-sensitized solar cell.
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ABSTRACT: We report the first case of Ru(II) dipyrrinates employed as dyes in dye-sensitized solar cells. These complexes exhibit panchromatic light harvesting that results in significant DSSC current densities, rendering them promising for photovoltaic applications. Adjustment of the lowest excited state energy is required to boost the power conversion efficiency.Chemical Communications 07/2012; 48(70):8790-2. · 6.17 Impact Factor -
Article: Cycloruthenated sensitizers: improving the dye-sensitized solar cell with classical inorganic chemistry principles.
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ABSTRACT: A divergence from the conventional approach to chromophore design has led to the establishment of many exciting new benchmarks for the dye-sensitized solar cell (DSSC), including the first documented power conversion efficiency in excess of 12% at 1 sun illumination [Yella et al., Science 2011, 334, 629]. Paramount to these advances is the deviation from polypyridyl ruthenium dyes bearing NCS(-) ligands, such as [Ru(dcbpy)(2)(NCS)(2)] (N3; dcbpy = 4,4'-dicarboxy-2,2'-bipyridine). While metal-free and porphyrin dyes have demonstrated much promise, the discovery that the NCS(-) ligands of N3 can be replaced by anionic, chelating cyclometalating ligands without compromising device efficiencies has ushered in a new era of ruthenium dye development. A particularly appealing feature of this class of dyestuff is that they offer acute control of the frontier molecular orbitals to enable the precise attenuation of both the ground and excited state redox potentials through judicious chemical modification of the aryl ring. This Perspective summarizes very recent developments in the field, and demonstrates how the new and rapidly expanding class of Ru-based sensitizers provides a conduit for enhancing the performance (and potentially the stability) of the DSSC.Dalton Transactions 05/2012; 41(26):7814-29. · 3.84 Impact Factor -
Article: Intramolecular hole transfer at sensitized TiO2 interfaces.
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ABSTRACT: Three ruthenium compounds with triphenyl amine donors were anchored to nanocrystalline TiO(2) thin films for interfacial electron-transfer studies. Molecular tuning of reduction potentials enabled the extent of hole transfer from the photo-oxidized ruthenium center to the triphenyl amine to be tuned from zero to unity. Kinetic data revealed two new insights into the unwanted interfacial recombination reaction of the injected electrons with the oxidized compounds. First, recombination was highly sensitive to the concentration of oxidized compounds present at the interface. Second, a significant enhancement of the open circuit photovoltage was realized without a change in the recombination kinetics, behavior attributed to translation of the hole away from the interface thereby generating a larger surface dipole.Journal of the American Chemical Society 05/2012; 134(20):8352-5. · 9.91 Impact Factor -
Article: Derivatization of bichromic cyclometalated Ru(II) complexes with hydrophobic substituents.
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ABSTRACT: The syntheses and physical properties of cyclometalated Ru(II) complexes containing a triphenylamine (TPA) unit bearing aliphatic groups are reported. Each member of the series consists of an octahedral Ru(II) center coordinated by a tridentate polypyridyl ligand and a tridentate cyclometalating ligand. One of the chelating ligands contains electron-deficient methyl ester groups, while a TPA unit is attached to the central ring of the adjacent chelating ligand through a thiophene bridge. This study builds on our previous work (Inorg. Chem. 2011, 50, 6019-6028; Inorg. Chem. 2011, 50, 5494-5508) by (i) outlining a synthetic protocol for installing aliphatic groups on the TPA substituents, (ii) examining the role that terminal -O-hexyl and -S-hexyl groups situated on the TPA have on the electrochemical properties, and (iii) demonstrating the potential benefit of installing the TPA on the neutral chelating ligand rather than the anionic chelating ligand. The results reported herein provide important synthetic advances for our broader goal of developing bis-tridentate cyclometalated Ru(II) complexes for light-harvesting applications.Inorganic Chemistry 02/2012; 51(3):1501-7. · 4.60 Impact Factor -
Article: Systematic modulation of a bichromic cyclometalated ruthenium(II) scaffold bearing a redox-active triphenylamine constituent.
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ABSTRACT: The syntheses and physicochemical properties of nine bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand furnished with terminal triphenylamine (TPA) substituents are reported. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(Me(3)tctpy)] (pbpy = 6-phenyl-2,2'-bipyridine; Me(3)tctpy = trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine), where various electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) are installed about the TPA unit and the anionic ring of the pbpy ligand. It is found that the redox chemistry of the Ru center and the TPA unit can be independently modulated by (i) placing EWGs (e.g., -CF(3)) or EDGs (e.g., -OMe) on the anionic ring of the pbpy ligand (substituted sites denoted as R(2) or R(3)) and/or (ii) installing electron-donating substituents (e.g., -H, -Me, -OMe) para to the amine of the TPA group (i.e., R(1)). The first oxidation potential is localized to the TPA unit when, for example, EDGs are placed at R(1) with EWGs at R(2) (e.g., the TPA(•+)/TPA(0) and Ru(III)/Ru(II) redox couples appear at +0.98 and +1.27 V vs NHE, respectively, when R(1) = -OMe and R(2) = -CF(3)). This situation is reversed when R(3) = EDG and R(1) = -H: TPA-based and metal-centered oxidation waves occur at +1.20 and +1.11 V vs NHE, respectively. The UV-vis spectrum for each complex is broad (e.g., absorption bands are extended from the UV region to beyond 800 nm in all cases) and intense (e.g., ε ∼ 10(4) M(-1)·cm(-1)) because of the overlapping intraligand charge-transfer and metal-to-ligand charge-transfer transitions. The information derived from this study offers guiding principles for modulating the physicochemical properties of bichromic cyclometalated ruthenium(II) complexes.Inorganic Chemistry 07/2011; 50(13):6019-28. · 4.60 Impact Factor -
Article: Design and development of functionalized cyclometalated ruthenium chromophores for light-harvesting applications.
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ABSTRACT: The syntheses and the electrochemical spectroscopic properties of a suite of asymmetrical bistridentate cyclometalated Ru(II) complexes bearing terminal triphenylamine (TPA) substituents are reported. These complexes, which contain structural design elements common to both inorganic and organic dyes that exhibit superior power conversion efficiencies in the dye-sensitized solar cell (DSSC), are broadly formulated as [Ru(II)(L-2,5'-thiophene-TPA-R(1))(L-R(2))](+) [L = tridentate chelating ligand (e.g., 2,2':6',2''-terpyridine (tpy); deprotonated forms of 1,3-di(pyridin-2-yl)benzene (Hdpb) or 6-phenyl-2,2'-bipyridine (Hpbpy)); R(1) = -H, -Me, -OMe; R(2) = -H, -CO(2)Me, -CO(2)H]. The following structural attributes were systematically modified for the series: (i) electron-donating character of the terminal substituents (e.g., R(1) = -H, -Me, -OMe) placed para to the amine of the "L-2,5'-thiophene-TPA-R(1)" ligand framework; (ii) electron-withdrawing character of the tridentate chelate distal to the TPA-substituted ligand (e.g., R(2) = -H, -CO(2)Me, -CO(2)H); and (iii) position of the organometallic bond about the Ru(II) center. UV-vis spectra reveal intense and broad absorption bands arising from a collection of metal-to-ligand charge-transfer (MLCT) and TPA-based intraligand charge-transfer (ILCT) transitions that, in certain cases, extend beyond 800 nm. Electrochemical data indicate that the oxidative behavior of the TPA and metal chelate units can be independently modulated except in cases where the anionic phenyl ring is in direct conjugation with the TPA unit. In most cases, the anionic character of the cyclometalating ligands renders a metal-based oxidation event prior to the oxidation of the TPA unit. This situation can, however, be reversed with an appropriately positioned Ru-C bond and electron-rich R(1) group. This finding is important in that this arrangement confines the highest occupied molecular orbital (HOMO) to the TPA unit rather than the metal, which is optimal for sensitizing TiO(2); indeed, a remarkably high power conversion efficiency (η) in the DSSC (i.e., 8.02%) is measured for the TPA-substituted pbpy(-) chelate where R(1) = -OMe. These results provide a comprehensive strategy for improving the performance of bistridentate Ru sensitizers devoid of NCS(-) groups for the DSSC.Inorganic Chemistry 06/2011; 50(12):5494-508. · 4.60 Impact Factor -
Article: Triphenylamine-modified ruthenium(II) terpyridine complexes: enhancement of light absorption by conjugated bridging motifs.
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ABSTRACT: The photophysical properties of a family of heteroleptic [Ru(tpy)(2)](2+) (tpy = 2,2':6',2''-terpyridine) complexes modified with triphenylamine donor units with different bridging units are reported.Inorganic Chemistry 06/2010; 49(12):5335-7. · 4.60 Impact Factor -
Article: Synthesis and characterisation of bis(beta-ketoaminato) complexes of cobalt(II).
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ABSTRACT: Condensation of 1-phenyl-1,3-butanedione with various substituted anilines affords N-aryl substituted beta-ketoamines PhC(O)CHC(CH(3))Naryl, which, when deprotonated and reacted with Co(OAc)(2).4H(2)O yields a series of bis(beta-ketoaminato)cobalt(II) complexes 1b to 6b (aryl = Ph, 1b; p-CH(3)C(6)H(4), 2b; 2,6-(CH(3))(2)C(6)H(3), 3b; 3,5-(CH(3))(2)C(6)H(3), 4b; p-CF(3)C(6)H(4), 5b; p-CH(3)OC(6)H(4), 6b). All six cobalt compounds were characterised by (1)H NMR, elemental analysis, magnetic susceptibility, and X-ray crystallography, indicating a uniform tetrahedral geometry in all cases. Electrochemical oxidation potentials indicate sensitivity to aryl substitution at the ortho- and para- positions, but not to meta-substitution, a conclusion supported by DFT calculations.Dalton Transactions 03/2010; 39(10):2573-8. · 3.84 Impact Factor -
Article: Systematic manipulation of the light-harvesting properties for tridentate cyclometalated ruthenium(II) complexes.
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ABSTRACT: The response of the metal-to-ligand charge-transfer (MLCT) band to variability in terminal substituents within a related set of tridentate polypyridyl and cyclometalated Ru(II) complexes is reported. These complexes are formulated as [Ru(tpy-R(1))(tpy-R(2))](PF(6))(2) (1-6; tpy = 2,2':6',2''-terpyridine; R(1) = -H, -2-furyl, or -OMe; R(2) = -H, -2-furyl, or -CO(2)H) and [Ru(tpy-R(2))(dpb-R(1))]PF(6) (7-10; Hdpb = 1,3-di(pyridin-2-yl)benzene; R(2) = -H or -2-furyl; R(1) = -H or -OMe). Absorption spectra for the [Ru(tpy-R(1))(tpy-R(2))](2+) series highlight the sensitivity of the MLCT band to the indicated substituents at the 4' position of one or both tpy ligands (e.g., a bathochromic shift up to 24 nm coupled with a 2-fold increase in absorption intensity). Similar observations are made for the [Ru(tpy-R(2))(dpb-R(1))](+) series, where a single Ru-N dative bond is replaced by a Ru-C sigma-bond to form a cyclometalated complex. The reduced symmetry at the metal center within this series results in a broadening of the lowest-energy MLCT band, while an additional set of transitions at higher energies emerges that involves an excited state localized on the cyclometalating ligand. These MLCT transitions collectively render a broad absorption envelope of substantial intensity at wavelengths longer than ca. 525 nm. Optimal results are obtained for compound 10 (R(1) = -OMe; R(2) = -2-furyl), where a strong electron-donating group is situated para to the Ru-C bond (lambda(max) = 523 nm; epsilon = 2.6 x 10(4) M(-1) cm(-1)). This approach imparts substantial polarization within the molecule, which should benefit excited-state electron-transfer reactions for photosensitizing applications (e.g., dye-sensitized solar cells). Spectroscopic data are corroborated by electrochemical and TD-DFT measurements for all compounds.Inorganic Chemistry 10/2009; 48(20):9644-52. · 4.60 Impact Factor -
Article: On the viability of cyclometalated Ru(II) complexes for light-harvesting applications.
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ABSTRACT: The effects of replacing a single polypyridyl ligand with an analogous anionic cyclometalating ligand were investigated for a set of three structurally related series of Ru(II) compounds formulated as [Ru(bpy)(2)(L)](z), [Ru(tpy)(L)](z), and [Ru(tpy)(L)Cl](z), where z = 0, +1, or +2, and L = polypyridyl (e.g., bpy = 2,2'-bipyridine, tpy = 2,2':6',2''-terpyridine) or cyclometalating ligand (e.g., deprotonated forms of 2-phenylpyridine or 3-(2-pyridinyl)-benzoic acid). Each of the complexes were synthesized and characterized by (1)H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and/or elemental analyses (EA). Cyclic voltammetry reveals that cyclometalation causes a shift of the first oxidation and reduction potentials by -0.5 to -0.8 V and -0.2 to -0.4 V, respectively, relative to their polypyridyl congeners. These disparate shifts have the effect of inducing a bathochromic shift of the lowest-energy absorption bands by as much as 90 nm. With the aid of time-dependent density functional theory (DFT), the lowest-energy bands (lambda(max) = 500-575 nm) were assigned as predominantly metal-to-ligand charge-transfer (MLCT) transitions from Ru to the polypyridyl ligands, while Ru-->C(wedge)NN (or C(wedge)N(wedge)N or N(wedge)C(wedge)N) transitions are found within the absorption bands centered at ca. 400 nm. The properties of a series of compounds furnished with carboxylic acid anchoring groups at various positions are also examined for applications involving the sensitization of metal-oxide semiconductors. It is determined that the thermodynamic potentials of many of these compounds are appropriate for conventional photoelectrochemical cells (e.g., dye-sensitized solar cells) that utilize a titania electrode and iodide-based electrolyte.Inorganic Chemistry 09/2009; 48(20):9631-43. · 4.60 Impact Factor -
Article: Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by beta-ketoiminate complexes of cobalt(II).
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ABSTRACT: Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.Chemistry - An Asian Journal 06/2009; 4(8):1257-65. · 4.50 Impact Factor
Top co-authors
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Institutions
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2009–2012
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The University of Calgary
- Department of Chemistry
Calgary, Alberta, Canada
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2010
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University of British Columbia - Vancouver
- Department of Chemistry
Vancouver, British Columbia, Canada
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