A double-heterostructure boron subphthalocyanine chloride (SubPc)/C60 thin-film photovoltaic cell exhibits a more than doubled V oc compared to a conventional copper phthalocyanine (CuPc)/C60 cell ...under 1 sun AM1.5G simulated illumination. The lower oxidation potential of SubPc results in an increase in the energy difference between the lowest unoccupied molecular orbital of the acceptor-like material and the highest occupied molecular orbital of the donor-like material (referred to as the interface gap, I g) by 400 meV. We attribute the significant increase in V oc to this increase in I g.
The lowest unoccupied molecular orbital (LUMO) energies of a variety of molecular organic semiconductors have been evaluated using inverse photoelectron spectroscopy (IPES) data and are compared with ...data determined from the optical energy gaps, electrochemical reduction potentials, and density functional theory (DFT) calculations. A linear fit to the electrochemical reduction potential (relative to an internal ferrocene reference) vs. the LUMO energy determined by IPES gives a slope and intercept of −1.19
±
0.08
eV/V and −4.78
±
0.17
eV, respectively, and 0.92
±
0.04 and −0.44
±
0.11
eV, respectively, based on the DFT calculated LUMO energies. From these fits, we estimate the LUMO and exciton binding energies of a wide range of organic semiconductors.
Small‐molecule solar cells are demonstrated using Pt and Pd tetraphenylbenzoporphyrin as donor materials. High efficiencies are achieved, and the effects of triplet excited state diffusion are ...studied. The solubility of these molecules allows for the fabrication of solution processed solar cells with relatively high performance.
The thermodynamics and kinetics of binding to nanocrystalline TiO2 were investigated for five ruthenium complexes that differed structurally in the number of possible anchoring carboxy groups (one, ...two, four, or six) attached to coordinated bipyridyl ligands and in the number of auxiliary ligands (bipyridine, CN-, or SCN-). Diffuse reflectance infrared spectroscopic data indicated that the dyes predominantly bound to TiO2 in a bridging mode in which the oxygen atoms of an attached carboxy group were bound to separate titanium atoms on the TiO2 surface. Furthermore, in the dry state, complexes with only one monocarboxy or dicarboxy ligand used essentially all of their available carboxy groups to bind to the surface. However, complexes having two or three dicarboxy ligands used on average two carboxylato groups in binding to TiO2. The structural differences between the complexes were manifested chemically in that the five dyes yielded similar maximum coverages (>100 nmol cm-2) on nanocrystalline TiO2 electrodes, but exhibited different binding constants (103−105 M-1) and different adsorption and desorption kinetics (3−11) × 103 M-1 h-1 and 1−100 h, respectively). The binding constant for the monocarboxy dye was significantly lower than the binding constants for dyes with dicarboxy ligands, correlating primarily with an increase in the desorption rate of the monocarboxy complex. The adsorption rate constants were similar for all of the dyes, suggesting that formation of the first bond to TiO2 was rate limiting. Binding of the dyes from an ethanolic solution that contained pyridine and pyridinium as an acidic proton activity buffer yielded lower coverages than binding from a nonbuffered ethanol solution, even though the binding constants were up to 100 times greater under buffered conditions. The lower equilibrium dye coverage in buffered ethanol did not correlate with changes in the protonation state of the dyes but rather indicated competition for, and/or deactivation of, TiO2 active sites in buffered ethanol. The more weakly bound monocarboxy dye displayed the lowest short-circuit current density and open-circuit voltage under simulated solar illumination in a photoelectrochemical cell containing 0.50 M LiI, 0.040 M I2, 0.020 M pyridine, and 0.020 M pyridinium triflate in acetonitrile. Additionally, even at constant coverage, the integrated quantum yield for photocurrent flow was lowest for TiO2 sensitized with the monocarboxy dye. The potential required to drive 0.1 mA cm-2 of cathodic current density in the dark on dye-sensitized TiO2 photoelectrodes was least negative for the monocarboxy dye, indicating more facile electron transfer between reduced TiO2 and the solution redox couple. Hence, in this series of ruthenium carboxy-bipyridyl dyes, the most weakly bound species (i.e., the monocarboxy dye) yielded inferior photoelectrode properties, whereas differences between the dyes that contained at least one dicarboxy ligand resulted primarily from differences in the light absorption and energetic properties of the metal complexes. These observations suggest an important role for the linkage to the TiO2 surface in achieving temporal stability as well as in tuning both the steady-state quantum yield and the magnitude of the predominant back-reaction rate in dye-sensitized TiO2-based photoelectrochemical solar cells.
We have shown that RuII(bpy)2(bpy-4-(xylyl) x -≡-phenyl-COOH)(PF6)2 (abbreviated Rux, where x = 0, 1 or 2 xylyl groups; bpy = 2,2‘-bipyridine) dyes can act as sensitizers for nanocrystalline TiO2 in ...functional photoelectrochemical cells under simulated solar illumination, albeit with low efficiencies. Both the short-circuit photocurrent density and the open-circuit voltage decreased as x was increased. Electron injection (106−108 s-1) was slightly faster for the x = 0 dye, but both recombination (10-15−10-13 cm3 s-1) and regeneration (104−106 s-1 for 10 mM I-) were slightly faster for the x = 2 dye. We suggest that the lack of distance dependence is due to the flexible one-carboxyl attachment to the surface resulting in the Ru−TiO2 electron-tunneling distance being very similar for x = 0, 1, and 2. For all of the Rux sensitizers, a relatively small potential was needed for generation of current in the dark, indicating that the reaction between electrons in TiO2 and the I3 -/I- electrolyte solution is as favorable for the Rux sensitizers as for unmodified TiO2 electrodes.
The World Health Organization recently defined hypertension and type 2 diabetes (T2D) as modifiable comorbidities leading to dementia and Alzheimer's disease. In the United States (US), hypertension ...and T2D are health disparities, with higher prevalence seen for Black and Hispanic minority groups compared to the majority White population. We hypothesized that elevated prevalence of hypertension and T2D risk factors in Black and Hispanic groups may be associated with dementia disparities. We interrogated this hypothesis using a cross-sectional analysis of participant data from the All of Us (AoU) Research Program, a large observational cohort study of US residents. The specific objectives of our study were: (1) to compare the prevalence of dementia, hypertension, and T2D in the AoU cohort to previously reported prevalence values for the US population, (2) to investigate the association of hypertension, T2D, and race/ethnicity with dementia, and (3) to investigate whether race/ethnicity modify the association of hypertension and T2D with dementia. AoU participants were recruited from 2018 to 2019 as part of the initial project cohort (R2019Q4R3). Participants aged 40-80 with electronic health records and demographic data (age, sex, race, and ethnicity) were included for analysis, yielding a final cohort of 125,637 individuals. AoU participants show similar prevalence of hypertension (32.1%) and T2D (13.9%) compared to the US population (32.0% and 10.5%, respectively); however, the prevalence of dementia for AoU participants (0.44%) is an order of magnitude lower than seen for the US population (5%). AoU participants with dementia show a higher prevalence of hypertension (81.6% vs. 31.9%) and T2D (45.9% vs. 11.4%) compared to non-dementia participants. Dominance analysis of a multivariable logistic regression model with dementia as the outcome shows that hypertension, age, and T2D have the strongest associations with dementia. Hispanic was the only race/ethnicity group that showed a significant association with dementia, and the association of sex with dementia was non-significant. The association of T2D with dementia is likely explained by concurrent hypertension, since > 90% of participants with T2D also had hypertension. Black race and Hispanic ethnicity interact with hypertension, but not T2D, to increase the odds of dementia. This study underscores the utility of the AoU participant cohort to study disease prevalence and risk factors. We do notice a lower participation of aged minorities and participants with dementia, revealing an opportunity for targeted engagement. Our results indicate that targeting hypertension should be a priority for risk factor modifications to reduce dementia incidence.
Studies of the electronic structure of titanium centers in titanium silicalite (TS-1) catalytic materials were carried out using electronic absorption and emission spectroscopy. A long-lived ...phosphorescent excited state with an emission maximum at 490 nm in the near UV was unambiguously assigned to the titanium. Resolved in the emission envelope was vibronic structure in 965 cm-1 mode, which corresponds to the Si−O−Ti stretching mode in TS-1. The lowest energy excited state is significantly lower in energy than was previously suggested by diffuse reflectance absorption spectroscopy. Emission excitation spectra indicate that, contrary to previous assertions, there are electronic transitions throughout the spectral region from ∼23000 to 48000 cm-1. These observations bring into question long-standing structural arguments for the coordination of titanium in the silicalite lattice that have been made using electronic spectroscopy.
Transition metal bis(acetylacetonate) complexes of Co(II), Ni(II), Cu(II), and Zn(II) have been found to be active catalysts for the sol−gel process. The catalytic activity of these complexes ...decreases in going from Co(II) to Zn(II) and is highest for the acetylacetonate ligand system. 29Si NMR studies show that the complexes act primarily as condensation catalysts and are, in that regard, similar to Brønsted bases such as hydroxide. Mechanistically, however, they appear to differ significantly from hydroxide in how they induce condensation. This is revealed in the catalyst concentration dependence, which is 1/2 order for the metal complexes and 1st order in hydroxide. Differences are also apparent in the thermochemical parameters that indicate that the metal complexes act to increase the entropy of the transition state leading to condensation. The catalytic activity is proportional to the degree of ligand dissociation of the metal complex, and experiments suggest that the active catalytic species is specifically the first dissociation product, MII(acac)+.
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