PubMed Health⌕ Search

Biomedical subjects

M Grätzel

Publications and source records attributed to M Grätzel.

At least 19 recordsLinked to original sources
PubMed2006

Efficient green-blue-light-emitting cationic iridium complex for light-emitting electrochemical cells.

A highly luminescent novel cationic iridium complex [iridium bis(2-phenylpyridine)(4,4'-(dimethylamino)-2,2'-bipyridine)]PF6 was synthesized and characterized using NMR, UV-visible absorption, and emission spectroscopy and electrochemical methods. This complex displays intense photoluminescence maxima in the green-blue region of the visible spectrum and exhibits unprecedented phosphorescence quantum yields, 80 +/- 10% with an excited-state lifetime of 2.2 mus in a dichloromethane solution at 298 K. Single-layer light-emitting electrochemical cells with the charged complex as conducting and electroluminescent material sandwiched between indium-tin oxide and Ag electrodes were fabricated, which emit green-blue light with an onset voltage as low as 2.5 V. Density functional theory calculations were performed to provide insight into the electronic structure of the [iridium bis(2-phenylpyridine)(4,4'-(dimethylamino)-2,2'-bipyridine)]PF6 complex, comparing these results with those obtained for [iridium bis(2-phenylpyridine)(4,4'-tert-butyl-2,2'-bipyridine)]PF6.

Journal Article↗
PubMed2006

Electronic structures and absorption spectra of linkage isomers of trithiocyanato (4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) ruthenium(II) complexes: a DFT study.

Black dye (BD), isomer 1 ([Ru(II)(H3-tctpy)(NCS)3](-1), where H3-tctpy = 4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)](-1), isomer 2 and 2', and [Ru(H3-tctpy))(SCN)3](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).

Journal Article↗
PubMed2006

Synthesis, characterization, and DFT-TDDFT computational study of a ruthenium complex containing a functionalized tetradentate ligand.

A ruthenium complex trans-[Ru(L)(NCS)2], L = 4,4' ''-di-tert-butyl-4',4' '-bis(carboxylic acid)-2,2':6',2' ':6' ',2' ''-quaterpyridine (N886), was synthesized and characterized by spectroscopic and electrochemical methods. The absorption spectrum of the N886 complex shows metal-to-ligand charge-transfer transitions in the entire visible region and quasi-reversible oxidation and reduction potentials at E(1/2) = +0.38 and -1.92 V vs ferrocene, respectively. The electronic spectra of the N886 complex were calculated by density functional theory (DFT)-time-dependent DFT, which qualitatively reproduces the experimental absorption spectra for both the protonated and deprotonated species. From the analysis of the computed optical transitions of N886, we assign its absorption bands as mixed Ru/SCN-to-quaterpyridine charge-transfer transitions, which extend from the near-IR to the UV regions. The panchromatic response of the N886 complex renders it as a suitable sensitizer for solar energy conversion applications based on titanium dioxide mesoporous electrodes. The preliminary results using the N886 complex as a sensitizer in a dye-sensitized solar cell, with an electrolyte containing 0.60 M butylmethylimidazolium iodide, 0.03 M I2, and 0.50 M tert-butylpyridine in a mixture of acetonitrile and valeronitrile (volume ratio 1:1), show 40% incident photon-to-current efficiencies, yielding under standard AM 1.5 sunlight a short-circuit photocurrent density of 11.8 +/- 0.2 mA/cm(2), an open-circuit voltage of 680 +/- 30 mV, and a fill factor of 0.73 +/- 0.03, corresponding to an overall conversion efficiency of 5.85%.

Journal Article↗
PubMed2005

Engineering of a novel ruthenium sensitizer and its application in dye-sensitized solar cells for conversion of sunlight into electricity.

A novel ligand 4,4'-bis(carboxyvinyl)-2,2'-bipyridine (L) and its ruthenium(II) complex [Ru(II)L(2)(NCS)(2)] (K8) were synthesized and characterized by analytical, spectroscopic, and electrochemical techniques. The performance of the K8 complex as a charge transfer photosensitizer in nanocrystalline TiO(2) based solar cells was studied. When the K8 complex anchored onto a nanocrystalline TiO(2) film, we achieved very efficient sensitization yielding 77 +/-5% incident photon-to-current efficiencies (IPCE) in the visible region using an electrolyte consisting of 0.6 M methyl-N-butyl imidiazolium iodide, 0.05 M iodine, 0.05 M LiI, and 0.5 M 4-tert-butylpyridine in a 50/50 (v/v) mixture of valeronitrile and acetonitrile. Under standard AM 1.5 sunlight, the complex K8 gave a short circuit photocurrent density of 18 +/- 0.5 mA/cm(2), and the open circuit voltage was 640 +/- 50 mV with fill factor of 0.75 +/- 0.05, corresponding to an overall conversion efficiency of 8.64 +/- 0.5%.

Journal Article↗
PubMed2004

Molecular control of recombination dynamics in dye-sensitized nanocrystalline TiO2 films: free energy vs distance dependence.

In this paper we address the dependence of the charge recombination dynamics in dye-sensitized, nanocrystalline TiO2 films upon the properties of the sensitizer dye employed. In particular we focus upon dependence of the charge recombination kinetics upon the dye oxidation potential E0(D+/D), determined electrochemically, and the spatial separation r of the dye cation HOMO orbital from the metal oxide surface, determined by semiempirical calculations. Our studies employed a series of ruthenium bipyridyl dyes in addition to porphyrin and phthalocyanine dyes. A strong correlation is observed between the recombination dynamics and the spatial separation r, with variation in r by 3 A resulting in a more than 10-fold change in the recombination half-time t(50%). This correlation is found to be in agreement with electron tunneling theory, t(50%) proportional, variant exp(-betar) with beta = 0.95 +/- 0.2 A-1. In contrast, the recombination dynamics were found to be relatively insensitive to variations in E0D+/D), indicative of the recombination reaction lying near the peak of the Marcus free energy curve, DeltaG approximately lambda, and with lambda approximately 0.8 eV. A correlation is also observed between the recombination half-time and the temporal shape of the kinetics, with faster recombination dynamics being more dispersive (less monoexponential). Comparison with numerical Monte Carlo type simulations suggests this correlation is attributed to a shift from fast recombination dynamics primarily limited by dispersive electron transport within the metal oxide film to slower dynamics primarily limited by the interfacial electron-transfer reaction. We conclude that the primary factor controlling the charge recombination dynamics in dye-sensitized, nanocrystalline TiO2 films is the spatial separation of the dye cation from the electrode surface. In particular, we show that for the Ru(dcbpy)2NCS2 dye series, the use of X = NCS rather than X = CN results in a 2 A shift in the dye cation HOMO orbital away from the electrode surface, causing a 7-fold retardation of the recombination dynamics, resulting in the remarkably slow recombination dynamics observed for this sensitizer dye.

Journal Article↗
PubMed2003

A swift dye uptake procedure for dye sensitized solar cells.

Solar cells based on swift self-assembled sensitizer bis(tetrabutylammonium)-cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid-2,2'-bipyridine)ruthenium(II) (N719) on double layers of 12 + 4 microm thick nanocrystalline TiO2 films exhibit the incident monochromatic photon-to-current conversion efficiency (IPCE) 90% and show a short circuit current density of 17 mA cm(-2), 750 mV open circuit potential and 0.72 fill factor yielding power conversion efficiencies over 9.18% under AM 1.5 sun. For the first time highest power conversion efficiencies are obtained for dye sensitized solar cells using a swift self-assembled procedure.

Journal Article↗
PubMed2002

Novel ruthenium sensitizers containing functionalized hybrid tetradentate ligands: synthesis, characterization, and INDO/S analysis.

Ruthenium sensitizers of the type trans-[Ru(L(1))(X)(2)], trans-[Ru(L(2))(X)(2)], trans-[Ru(L(3))(X)(2)], and trans-[Ru(L(4))(X)(2)] (where L(1) = 6,6'-bis(1-H-benzimidazol-2-yl)-4,4'-bis(methoxycarbonyl)-2,2'-bipyridine, L(2) = 4,4' "-bis(tert-butyl)-4',4' '-bis[p-(methoxycarbonyl)phenyl]-2,2':6',2' ':6' ',2' "-quaterpyridine, L(3) = 4',4' '-bis[3,4-(dimethoxy)phenyl]-2,2':6',2' ':6' ',2' "-quaterpyridine, and L(4) = 4',4' '-diethoxycarbonyl-2,2':6',2' ':6' ',2' "-quaterpyridine; X = Cl(-), NCS(-)) were synthesized and characterized by CV, NMR, and UV-vis absorption and emission spectroscopy. The trans-dichloro and dithiocyanate complexes show MLCT transitions in the entire visible and near-IR region. The lowest energy metal-to-ligand charge-transfer transition band of the trans-dichloro complexes is around 14 300 cm(-1) in DMF solution, and these complexes show weak and broad emission signals with onset at above 10 500 cm(-1). The absorption and emission maxima of the trans-dithiocyanate complexes are blue-shifted compared to those of its trans-dichloro analogues because of the strong pi acceptor property of the NCS(-) compared to the Cl(-). The electronic spectra of trans-[Ru(L)(X)(2)] complexes were calculated by INDO/S and compared with the experimental data. The extent of mixing between metal 4d and ligand pi orbitals is discussed. Extensive pi-back-donation is observed. The panchromatic response of these novel complexes renders them as suitable sensitizers for solar energy conversion applications based on titanium dioxide mesoporous electrodes. Preliminary results using the trans-[Ru(L(4))(NCS)(2)] complex show 75% incident photon-to-current efficiencies (IPCE), yielding 18 mA/cm(2) current density under standard AM 1.5 sunlight.

Journal Article↗
PubMed2001

Photoelectrochemical cells.

Until now, photovoltaics--the conversion of sunlight to electrical power--has been dominated by solid-state junction devices, often made of silicon. But this dominance is now being challenged by the emergence of a new generation of photovoltaic cells, based, for example, on nanocrystalline materials and conducting polymer films. These offer the prospect of cheap fabrication together with other attractive features, such as flexibility. The phenomenal recent progress in fabricating and characterizing nanocrystalline materials has opened up whole new vistas of opportunity. Contrary to expectation, some of the new devices have strikingly high conversion efficiencies, which compete with those of conventional devices. Here I look into the historical background, and present status and development prospects for this new generation of photoelectrochemical cells.

Journal Article↗
PubMed2001

Engineering of efficient panchromatic sensitizers for nanocrystalline TiO(2)-based solar cells.

A new series of panchromatic ruthenium(II) sensitizers derived from carboxylated terpyridyl complexes of tris-thiocyanato Ru(II) have been developed. Black dye containing different degrees of protonation [(C(2)H(5))(3)NH][Ru(H(3)tcterpy)(NCS)(3)] 1, [(C(4)H(9))(4)N](2)[Ru(H(2)tcterpy)(NCS)(3)] 2, [(C(4)H(9))(4)N](3)[Ru(Htcterpy)(NCS)(3)] 3, and [(C(4)H(9))(4)N](4)[Ru(tcterpy)(NCS)(3)] 4 (tcterpy = 4,4',4' '-tricarboxy-2,2':6',2' '-terpyridine) have been synthesized and fully characterized by UV-vis, emission, IR, Raman, NMR, cyclic voltammetry, and X-ray diffraction studies. The crystal structure of complex 2 confirms the presence of a Ru(II)N6 central core derived from the terpyridine ligand and three N-bonded thiocyanates. Intermolecular H-bonding between carboxylates on neighboring terpyridines gives rise to 2-D H-bonded arrays. The absorption and emission maxima of the black dye show a bathochromic shift with decreasing pH and exhibit pH-dependent excited-state lifetimes. The red-shift of the emission maxima is due to better pi-acceptor properties of the acid form that lowers the energy of the CT excited state. The low-energy metal-to-ligand charge-transfer absorption band showed marked solvatochromism due to the presence of thiocyanate ligands. The Ru(II)/(III) oxidation potential of the black dye and the ligand-based reduction potential shifted cathodically with decreasing number of protons and showed more reversible character. The adsorption of complex 3 from methoxyacetonitrile solution onto transparent TiO(2) films was interpreted by a Langmuir isotherm yielding an adsorption equilibrium constant, K(ads), of (1.0 +/- 0.3) x 10(5) M(-1). The amount of dye adsorbed at monolayer saturation was (n(alpha) = 6.9 +/- 0.3) x 10(-)(8) mol/mg of TiO(2), which is around 30% less than that of the cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) complex. The black dye, when anchored to nanocrystalline TiO(2) films achieves very efficient sensitization over the whole visible range extending into the near-IR region up to 920 nm, yielding over 80% incident photon-to-current efficiencies (IPCE). Solar cells containing the black dye were subjected to analysis by a photovoltaic calibration laboratory (NREL, U.S.A.) to determine their solar-to-electric conversion efficiency under standard AM 1.5 sunlight. A short circuit photocurrent density obtained was 20.5 mA/cm(2), and the open circuit voltage was 0.72 V corresponding to an overall conversion efficiency of 10.4%.

Journal Article↗
PubMed2000

Molecular photovoltaics.

The dye-sensitized nanocrystalline injection solar cell employs transition metal complexes for spectral sensitization of mesoporous TiO(2) films together with suitable redox electrolytes or amorphous organic hole conductors. Light harvesting occurs efficiently over the whole visible and near-IR range due to the very large internal surface area of the films. Judicious molecular engineering allows the photoinduced charge separation to occur quantitatively within a few femtoseconds. The certified overall power conversion efficiency of the new solar cell for AM 1.5 solar radiation stands presently at 10.4%.

Coloring Agents↗
PubMed1999

Surface Modification of a Hydrogen-Bonded Pigment: A Fluorescence Spectroscopy Study.

The effect of hydrogen-bonding additives on the surface modification of a hydrogen-bonded organic pigment is studied using absorption and fluorescence spectroscopy. Evidence for surface dissolution that occurs during the mixing of solids is presented. The spectral signatures of monomers and hydrogen-bonded aggregates of the pigment that are present on the surface of crystallites of the pigment are quite distinct, as revealed by fluorescence excitation and emission spectra. Copyright 1999 Academic Press.

Journal Article↗
PubMed1997

Light induced redox reactions involving mammalian ferritin as photocatalyst.

Under excitation by visible light the iron storage protein ferritin catalyses the reduction of cytochrome c and viologens as well as the oxidation of carboxylic acids, thiol compounds, and sulfite. The photochemically active element of ferritin is its mineral ferrihydrite semiconductor core. Band-gap excitation of these microcrystals leads to generation of electron-hole pairs that are sufficiently long-lived and reactive to engage in redox reactions with components of the medium. Photoreduction of cytochrome c and viologens occurs due to electron transfer from the conduction band of the iron oxide cluster through the protein shell surrounding the ferritin core. Laser photolysis coupled with time-resolved kinetics spectroscopy showed the electron transfer to propylviologen sulfonate to proceed in the microsecond time range. In the absence of electron acceptor at pH < 7, light excitation results in photodissolution of the iron oxide cluster with concomitant formation of Fe(II). These novel findings concerning the photocatalytic activity of ferritin with its inherent biological implications are discussed.

Animals↗
PubMed1996

Glucose oxidase mediation by soluble and immobilized electroactive detergents.

A series of novel, surface-active, inorganometallic complexes of osmium were synthesized and then characterized (using electrochemical techniques) as electron transfer mediators for glucose oxidase (EC 1.1.3.4, GOD) from Aspergillus niger. The mediators contain a dipyridylamine ligand bearing (on the amine nitrogen) a saturated alkyl chain (typically C5 to C12), omega-terminated with either a methyl group or a functional group such as carboxyl or hydroxyl. Such compounds displayed subtle differences in their interactions with GOD. The presence of a omega-functional group tended to diminish a mediator's micelle-forming activity, but also concomitantly decreased the denaturing action of the mediator towards the protein structure of GOD. However, the presence of an ionised carboxyl group slowed GOD mediation relative to that of a similar mediator bearing a methyl-terminated long alkyl chain, probably because of the additional negative charge. The omega-carboxyl functionality allowed covalent coupling of mediators to NH2-bearing graphite electrodes. GOD was co-immobilized and the resulting, reagentless, glucose-sensitive electrodes were characterized. Immobilization of the mediator did not appear to affect unduly the ability to mediate GOD. Additionally, complexes were directly coupled to lysine groups of GOD to give a self-mediating enzyme.

Biosensing Techniques↗
PubMed1994

Site of dopamine D1 receptor binding to Gs protein mapped with synthetic peptides.

We have synthesized peptides corresponding to the known sequence of the rat dopamine D1 receptor and measured the effects on binding of the Gs protein to the activated receptor. Peptides corresponding to the second and third cytoplasmic loop (amino acids 160-180 and 260-276), as well as the N-terminal part of the carboxy terminus (amino acids 375-391) were effective in preventing Gs binding to the activated receptor. Peptides representing other surface regions, e.g., the first cytoplasmic loop (87-100), the C-terminus (400-420 and 440-460) and all extracellular surface peptides (6-22, 120-137, 210-224 and 338-352) are not involved in rat dopamine D1 receptor-Gs protein interaction.

Amino Acid Sequence↗
PubMed1994

A novel immunosensor for herpes viruses.

We have developed a reusable piezoelectric immunosensor for the detection of the following human herpes viruses: herpes simplex viruses types 1 and 2, varicella-zoster virus, Epstein-Barr virus, and cytomegalovirus. Synthetic peptides, representing different surface antigens of the five viruses, were used to generate virus-specific monoclonal antibodies. Apply an antibody layer via protein A immobilization onto a 10-MHz AT-cut crystal resulted in 5 x 10(4)-1 x 10(9) viruses on the electrode surface in a linear frequency change and a long-term stability of 8 weeks when the modified crystal was stored dry over silica gel blue at room temperature. Under these conditions, the coated crystal can be used 18 times without detectable loss of activity.

Antibodies, Monoclonal↗
PubMed1992

Mediation of glycosylated and partially-deglycosylated glucose oxidase of Aspergillus niger by a ferrocene-derivatised detergent.

A ferrocene-derivatised detergent, (11-ferrocenylundecyl) trimethylammonium bromide (FTMAB), when oxidised to the corresponding ferricinium ion, was found by electrochemical studies to be an effective electron acceptor for reduced glucose oxidase of Aspergillus niger (EC 1.13.4) and thus acts as a electron-transfer mediator between glucose oxidase and a working electrode held at a potential sufficiently positive to reoxidise reduced FTMAB. An increase in mediating activity was produced when FTMAB was present in concentrations above its critical micelle concentration. An 'enzyme electrode' was formed by adsorption of glucose oxidase and FTMAB surfactant on a graphite rod. The electrode functioned as an amperometric biosensor for glucose in phosphate-buffered saline solution. A mixed micelle of glucose oxidase and FTMAB, probably adsorbed on the electrode surface, appears to be advantageous for the amperometric determination of glucose. Additionally, glucose oxidase was treated with alpha-mannosidase. When this partially-deglycosylated glucose oxidase was incorporated in an enzyme electrode, a 100-fold increase in the second-order rate constant (k) for electron transfer between the enzyme and FTMAB was observed, together with increased current densities, with respect to the equivalent values for FTMAB and commercial glucose oxidase. The use of deglycosylated enzymes in biosensors is suggested.

Aspergillus niger↗