Biomedical subjects

Elena Galoppini

Publications and source records attributed to Elena Galoppini.

8 recordsLinked to original sources

PubMed2006

Fast electron transport in metal organic vapor deposition grown dye-sensitized ZnO nanorod solar cells.

The electron transport in dye-sensitized solar cells with a MOCVD (metal organic vapor deposition)-grown ZnO nanorod array (ZnO-N) or a mesoporous film prepared from ZnO colloids (ZnO-C) as the working electrode was compared. The electrodes were of similar thickness (2 mum) and sensitized with zinc(II) meso-tetrakis(3-carboxyphenyl)porphyrin, while the electrolyte was I(-)/I(3)(-) in 3-methoxypropionitrile. Electron transport in the ZnO-C cells was comparable with that found for colloidal TiO(2) films (transport time approximately 10 ms) and was light intensity dependent. Electron transport in solar cells with ZnO-N electrodes was about 2 orders of magnitude faster ( approximately 30 mus). Thus, the morphology of the working ZnO electrode plays a key role for the electron transport properties.

Letter↗

PubMed2006

Pyrene-terminated phenylenethynylene rigid linkers anchored to metal oxide nanoparticles.

Phenylenethynylene (PE) rigid linkers (para and meta) were used to anchor pyrene to the surface of TiO2 (anatase) and ZrO2 nanoparticle thin films through the two COOH groups of an isophthalic acid (Ipa) unit. Four chromophore-linker models were studied in solution and bound. Two are novel meta-pyrene-PE linker systems: dimethyl 5-(3-(1-pyrenylethynyl)phenylethynyl)-isophthalate, carrying one pyrene, and dimethyl 5-(bis-3,5-(1-pyrenylethynyl)phenylethynyl)-isophthalate, carrying two. These were compared with para rigid-rods dimethyl 5-(1-pyrenylethynyl)isophthalate and dimethyl 5-(4-(1-pyrenylethynyl)phenylethynyl)-isophthalate, each carrying one pyrene but varying in length. The length of the PE linkers and the para or meta substitution influence the photophysical properties of the compounds. The extinction coefficient increased, and the long wavelength absorbance of the pyrene chromophore was shifted to the red with increasing conjugation. Compared to unsubstituted pyrene, the pyrene-linker systems were characterized by short fluorescence lifetimes (tau approximately 2 ns in tetrahydrofuran solutions), but quantum yields were close to unity. ZINDO/S CI calculations attribute this effect to a switching in the order of the two lowest-lying singlet states of pyrene. High surface coverages, approximately 10(-8) mol/cm2, and carboxylate binding modes on nanostructured TiO2 films were obtained in all cases. The appearance of a pyrene excimer emission on ZrO2, an insulator, indicates that the pyrene-linker system is closely packed (Py-Py < 4 A) on the surface. The fluorescence emission on TiO2 was completely quenched, consistent with quantitative and rapid electron injection into the semiconductor indicating that the pyrene excimer acts as a sensitizer. Photoelectrochemical studies in regenerative solar cells with I3-/I- as the redox mediator indicated near-quantitative conversion of absorbed photons into an electrical current.

Adsorption↗

PubMed2006

Tuning open circuit photovoltages with tripodal sensitizers.

The sensitizers [Ru(bpy)2(deeb)](PF6)2 (1), [Ru(bpy)2(bpy)-(E-Ph)-Ad](PF6)2 (2), and [Ru(bpy)2(bpy)-(E-Ph)2-Ad](PF6)2 (3), where deeb is 4,4'-(COOCH2CH3)2-2,2'-bipyridine, E-Ph is phenylethynyl, and Ad are tripod shaped bpy ligands based on 1,3,5,7-tetraphenyladamantane, were anchored to mesoporous nanocrystalline (anatase) TiO2 thin films and studied in regenerative solar cells with 0.1 M LiI/0.005 M I2 dichloromethane electrolyte. Over three decades of 488 nm irradiance, the open circuit photovoltage increased markedly with the distance between the Ru center and the surface binding groups, 1 (7 A) < 2 (18 A) < 3 (24 A). The diode equation accurately models the irradiance dependent data and indicates that the TiO2(e-) --> I3- (and/or I2) charge recombination rate constants were decreased by a factor of 20 for 2/TiO2 and 280 for 3/TiO2 relative to 1/TiO2. The results suggest that control of the sensitizer-TiO2 orientation is important for efficient power optimization.

Letter↗

PubMed2006

Binding studies of molecular linkers to ZnO and MgZnO nanotip films.

Two bifunctional linkers, a rigid-rod p-ethynyl-isophthalic acid capped with a Ru(II)-polypyridyl complex and 3-mercaptopropionic acid, were covalently bound to ZnO nanotip films grown by metal-organic chemical vapor deposition (MOCVD) technology. This highly vertically aligned, crystalline form of ZnO had not been functionalized before. The binding was studied by Fourier transform (FT) IR and UV spectroscopies and probed, in the case of the Ru complex, by static and dynamic fluorescence quenching. The molecules did bind through the carboxylic acid groups, and the FT-IR attenuated total reflectance spectra are indicative of a bidentate carboxylate binding mode. Other molecules (heptanoic acid, isophthalic acid, and trimethoxy(2-phenylethyl)silane) were also bound to the ZnO nanotips. A comparison was made with epitaxial ZnO films grown by MOCVD and ZnO mesoporous films prepared from colloidal solutions to investigate the effect of the ZnO morphology. The ZnO nanotips were excellent binding substrates, particularly for the rigid-rod linker. Since ZnO films are etched at low pH (< 4), novel nanotip films made of ternary MgxZn1-xO, which is formed by alloying ZnO with MgO and is more resistant to acids, were developed. The MgxZn1-xO nanotip films were employed to use linkers with acidic groups and to study the effect of pH pretreatment of the surface on the binding.

Journal Article↗

PubMed2004

Hybrid photoactive assemblies: electron injection from host-guest complexes into semiconductor nanoparticles.

Novel ternary assemblies consisting of fully encapsulated host-guest complexes (hemicarceplexes) and wide band gap semiconductor nanoparticles were investigated. The water-soluble amphiphilic host (octacarboxyhemicarcerand) traps the hydrophobic chromophore within its cavity and binds to the surface of metal oxide nanoparticles. Fluorescence quenching and fast charge injection, kforward >/= 7 x 109 s-1, from the S2 state of encapsulated azulene were observed. Charge recombination proceeds at a much lower rate of 2 x 107 s-1. Interestingly, the recombination kinetics is homogeneous, suggesting that electron tunneling through the wall of the "molecular container" is the rate-limiting step of the process.

Journal Article↗

PubMed2003

Subpicosecond photoinduced charge injection from "molecular tripods" into mesoporous TiO2 over the distance of 24 angstroms.

Extended rigid tripodal sensitizers were used to investigate the rate of long-distance photoinduced charge transfer from the MLCT excited states of RuII-based chromophores into mesoporous TiO2 films. The distance between the RuII center and the surface of the semiconductor was 24 A. Rapid biexponential charge injection with a major subpicosecond component as fast as 240 fs was observed upon femtosecond laser excitation of the tripods bound to the TiO2 surface. This rate exceeds the typical rates of vibrational cooling and thus strongly supports the possibility of "hot electron injection" occurring at very large donor-to-semiconductor distances.

Journal Article↗

PubMed2003

Molecular tectonics. Use of the hydrogen bonding of boronic acids to direct supramolecular construction.

Tetraboronic acids 1 and 2 have four -B(OH)(2) groups oriented tetrahedrally by cores derived from tetraphenylmethane and tetraphenylsilane. Crystallization produces isostructural diamondoid networks held together by hydrogen bonding of the -B(OH)(2) groups, in accord with the tendency of simple arylboronic acids to form cyclic hydrogen-bonded dimers in the solid state. Five-fold interpenetration of the networks is observed, but 60% and 64% of the volumes of crystals of tetraboronic acids 1 and 2, respectively, remain available for the inclusion of disordered guests. Guests occupy two types of interconnected channels aligned with the a and b axes; those in crystals of tetraphenylmethane 1 measure approximately 5.9 x 5.9 A(2) and 5.2 x 8.6 A(2) in cross section at the narrowest points, whereas those in crystals of tetraphenylsilane 2 are approximately 6.4 x 6.4 A(2) and 6.4 x 9.0 A(2). These channels provide access to the interior and permit guests to be exchanged quantitatively without loss of crystallinity. Because the Si-C bonds at the core of tetraboronic acid 2 are longer (1.889(3) A) than the C-C bonds at the core of tetraboronic acid 1 (1.519(6) A), the resulting network is expanded rationally. By associating to form robust isostructural networks with predictable architectures and properties of porosity, compounds 1 and 2 underscore the usefulness of molecular tectonics as a strategy for making ordered materials.

Journal Article↗

PubMed2002

Long-range electron transfer across molecule-nanocrystalline semiconductor interfaces using tripodal sensitizers.

Four tripodal sensitizers, Ru(bpy)(2)(Ad-tripod-phen)(2+) (1), Ru(bpy)(2)(Ad-tripod-bpy)(2+) (2), Ru(bpy)(2)(C-tripod-phen)(2+) (3), and Ru(bpy)(2)(C-tripod-bpy)(2+) (4) (where bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and Ad-tripod-bpy (phen) and C-tripod-bpy (phen) are tripod-shaped bpy (phen) ligands based on 1,3,5,7-tetraphenyladamantane and tetraphenylmethane, respectively), have been synthesized and characterized. The tripodal sensitizers consist of a rigid-rod arm linked to a Ru(II)-polypyridine complex at one end and three COOR groups on the other end that bind to metal oxide nanoparticle surfaces. The excited-state and redox properties of solvated and surface-bound 1-4 have been studied at room temperature. The absorption spectra, emission spectra, and electrochemical properties of 1-4 in acetonitrile solution are preserved when 1-4 are bound to nanocrystalline (anatase) TiO(2) or colloidal ZrO(2) mesoporous films. This behavior is indicative of weak electronic coupling between TiO(2) and the sensitizer. The kinetics for excited-state decay are exponential for 1-4 in solution and are nonexponential when 1-4 are bound to ZrO(2) or TiO(2). Efficient and rapid (k(cs) > 10(8) s(-)(1)) excited-state electron injection is observed for 1-4/TiO(2). The recombination of the injected electron with the oxidized Ru(III) center is well described by a second-order kinetic model with rate constants that are independent of the sensitizer. The sensitizers bound to TiO(2) were reversibly oxidized electrochemically with an apparent diffusion coefficient approximately 1 x 10(-11) cm(2) s(-)(1).

Journal Article↗