Multielectron redox chemistry of a neutral, NIR-active, indigo-pillared Re(I)-based triangular metalloprism.

Self-assembled, hexarhenium(I), triangular metalloprism compound [{(CO)(3)Re(µ-2)Re(CO)(3)}(3)(µ(3)-1)(2)] (3) featuring three bis-chelating pillarlike indigo dianions (µ-2), each of which connects two fac-Re(CO)(3) cores, which are interconnected by a tritopic N donor, that is, a 2,4,6-tris(4-pyridyl)-1,3,5-triazine (µ(3)-1, tPyTz) ligand, has been synthesized in high yield and characterized. Metalloprism 3 exhibits a strong absorption in the near-infrared (NIR) region. The reversible, multielectron redox properties of the electrogenerated 3(n) species, where n=3+, 0, 3-, 4-, 5-, 8-, in the visible and especially in the NIR region were investigated in THF solution by cyclic voltammetry (CV), chronocoulometry, EPR spectroscopy, and thin-layer UV/Vis/NIR spectroelectrochemistry (SEC). Stepwise, site-specific electrochemical reductions lead to the formation of a series of highly stable ion (radical) species in which electrons associated with µ-2 or µ(3)-1 components of the molecule can be clearly distinguished. An EPR investigation revealed interaction of unpaired electrons with the metal nuclei ((185,187)Re, I=5/2) in the reduced intermediates. The framework has C(2) symmetry, and accidental degeneracies suffice. Detailed theoretical calculations by structure-based DFT confirm that the triply degenerate HOMO has ≥70% indigo character with a sizable dπ-Re character, while the LUMO is dominated by the triply degenerate indigo ligands, and the LUMO+1 by doubly degenerate tPyTz ligands. A comparison of 3 and previously reported 2,2'-bis-benzimidazolate- (BiBzlm) or alkoxy-pillared Re(I) metalloprisms indicates a very low switching potential with a potential window of less than 1 V and reversibly accessible optical properties with higher stability of the intermediates. The properties exhibited by 3 appear to be due to the slight tuning of the bridging ligand from N,N(-) to N,O(-).

Isomeric Pyrene-Porphyrins for Efficient Dye-Sensitized Solar Cells: An Unexpected Enhancement of the Photovoltaic Performance upon Structural Modification.

Four pyrene-porphyrins were synthesized to study the isomer effect on the photovoltaic performance of dye-sensitized solar cells. One of these porphyrins is conjugated with a terminal pyrene, whereas the other three are each attached with a pyrene bearing an extra donor group. According to the positions of the extra donor and porphyrin core on pyrene, the 1,6-, 1,8-, and 2,7-isomers were compared for their fundamental and photovoltaic properties. For fundamental properties, UV-visible absorption, fluorescence emission, electrochemistry, and DFT calculations were carried out. For photovoltaic measurements, the seemingly inferior 1,8-isomer outperforms others with an overall efficiency of 10.30% under one-sun irradiation. Superior photovoltaic performance of the 1,8-isomeric dye may be related to the so-called umbrella effect. The findings of this work may provide insight into isomeric dye design for future applications.

Quinonoid-bridged chair-shaped dirhenium(I) metallacycles: synthesis, characterization, and spectroelectrochemical studies.

Self-assembled, chair-shaped dirhenium(I) macrocyclic compounds featuring the two different bis-chelating quinone dianions (1, L = dhnq(2-); 2, L = dhaq(2-); H(2)dhnq = 6,11-dihydroxy-5,12-naphthacenedione; H(2)dhaq = 1,4-dihydroxy-9,10-anthraquinone) that interface with two fac-Re(CO)(3) cores and a ditopic semirigid N-donor 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)naphthalene (L' = p-NBimM) ligand coordinated to the remaining orthogonal site were prepared in high yields. Their structures were confirmed by single-crystal X-ray diffraction analysis. Electrochemical assessments, using cyclic voltammetry (CV) and UV-vis-NIR spectroelectrochemistry (SEC), revealed the existence of two well-separated, single-electron quinone ligand-centered, reversibly accessible 0, -1, and -2 redox states. Among the two singly reduced radical complexes, the symmetrically bridged quinone complex 1(•-), showed a strong absorption in the NIR regions, which was not observed for the neutral and doubly reduced states, analogous to that of the free dhnq(3•-) quinone. In contrast, when 2 was reduced to 2(•-), a broad signal at 866 nm was observed, very similar to the reduced dhaq(3•-) quinone. This difference in spectral behavior in the singly reduced states is likely due to the annealed benzene ring in 1 and dhnq(2-) because of its symmetrical π-electron system, which is perturbed to a lesser degree compared to asymmetric 2 and dhaq(2-). Reduction to 1(•-) produces a small but not negligible g factor anisotropy (Δg = 0.024) in the electron spin resonance (ESR) signal, indicative of a very small metal-centered spin (5%), but 2(•-) shows a g value in the expected range for organic radicals (no detectable Δg). Thus, the combined investigations reveal that the singly reduced metallacycles are best described as being highly stable, noncommunicating, localized, quinonoid-centered radical complexes, [(CO)(3)Re(I)(µ-L(3•-))(µ-L')Re(I)(CO)(3)](•-).

Effects of potential shift and efficiency of charge collection on nanotube-based porphyrin-sensitized solar cells with conjugated links of varied length.

For dye-sensitized solar-cell devices fabricated from porphyrin sensitizers with links of varied length (PE1-PE4) adsorbed on anodic titanium-oxide nanotube arrays, we measured induced photocurrent and photovoltage decays under constant bias illumination; the evaluated efficiencies of charge collection of the devices show a systematic trend PE4 > PE3 > PE2 > PE1 at a large short-circuit current, implying that a long link would improve the charge separation if the electrons were effectively injected into the semiconductor.

Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO(2) and Al(2)O(3) nanotube arrays.

Porphyrins with phenylethynyl links of varied length (PE1-PE4) were sensitized on vertically oriented, anodic titanium-oxide (ATO) nanotube arrays for application as dye-sensitized solar cells (DSSC). The efficiency of power conversion decreased systematically from the dye with a short link to the dye with a long link. We measured the efficiency of conversion of incident photons to current (IPCE), the photocurrent decay of the devices, and steady-state and time-resolved fluorescence spectra of the thin-film samples to understand how the cell performance depends on the length of the link. Measurements of femtosecond fluorescence confirmed that the efficiency of electron injection depended on length because of dye aggregation that significantly increased the rate of aggregate-induced energy transfer for porphyrins with a long link. The rate of electron injection depended on the length of the link with an attenuation factor beta approximately 0.1 A(-1). Resonant energy transfer (RET) kinetics of porphyrins sensitized on anodic aluminium-oxide (AAO) nanotube arrays were performed with picosecond time-correlated single-photon counting and four molecular densities for each porphyrin. The kinetic data of PE1 and PE2 are described satisfactorily according to a Förster model, whereas those of PE3 and PE4 conform to a Dexter formula. A formation of clusters is proposed to rationalize the observed density-dependent kinetics for the RET of porphyrins on semiconductor films.

Fabrication of bacteriochlorin shell/gold core nanoparticles for the sensitive determination of trichlosan using differential pulse voltammetry.

The triclosan contamination in daily life has attracted great attention, and there is rare electroanalytical assay based on π-system dyes. In this work, a facile preparation and electroanalytical application of an organic dispersion containing bacteriochlorin dyes (LS11) and gold nanoparticles (AuNPs) was proposed. The organic-inorganic hybrid nanocomposites were characterized by transmission electron microscope (TEM) showing a core-shell structure with a uniform layer of dye molecules. The as-prepared nanocomposites were successfully coated onto glassy carbon electrodes, and the surface characteristics of the top most layer of the modified electrodes were examined by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and water contact angle experiments. The nanocomposite film-modified electrodes exhibited good electrochemical activity towards oxidation of triclosan. The oxidation of adsorbed triclosan occurred at a reduced overpotential, and the anodic current responses under a pre-concentration step prior to the potential scan were used for quantitative analysis. A good linear relationship from 0.01 µM to 0.5 µM was obtained using differential pulse voltammetry. The sensitivity and detection limit (S/N = 3) were 23.69 µA µM-1 and 0.03 µM, respectively. The proposed assay was applied to detect triclosan in two personal hygiene products using standard addition method, and the results showed good recoveries that ranged from 96.6% to 101.5% and from 99.3% to 103.8% for a toothpaste sample and a hand wash sample, respectively. A reference HPLC-UV method was used to evaluate the proposed electroanalytical method, and a good agreement was achieved.

Synthesis, properties and photovoltaic performance in dye-sensitized solar cells of three meso-diphenylbacteriochlorins bearing a dual-function electron-donor.

Bacteriochlorins are crucial to photosynthesis in bacteria. Studies of air-stable, meso-substituted bacteriochlorins are rare. We herein report the synthesis, properties, and photovoltaic performance of three new air-stable, meso-substituted bacteriochlorins bearing a dioctylfluorenylethyne (denoted as LS-17), a dioctylaminophenylethynylanthrylethyne (LS-43), and a diarylaminoanthrylethyne (LS-45) as the electron-donating groups. Among these LS-bacteriochlorins, LS-17 displays sharp UV-visible absorption bands whereas LS-43 and LS-45 give rise to broadened and red-shifted absorptions. Electrochemical and DFT results suggest that the first oxidation and reduction reactions of these bacteriochlorins are consistent with the formation of the cation and anion radicals, respectively. For dye-sensitized solar cell applications, photovoltaic performance of the LS-45 cell achieves an overall efficiency of 6.04% under one-sun irradiation.

Ground and excited electronic states of quininone-containing Re(I)-based rectangles: a comprehensive study of their preparation, electrochemistry, and photophysics.

The self-assembly of two rectangular compounds [{(CO)(3)Re(mu-QL)Re(CO)(3)}(2)(mu-bpy)(2)] (1, QL = 6,7-dimethyl 1,4-dioxido-9,10-anthraquinone (QL(1)); 2, QL = 1,4-dioxido-9,10-anthraquinone (QL(2)), bpy = 4,4'-bipyridine) via an orthogonal-bonding approach was achieved in high yields. Their structures were characterized by single-crystal X-ray diffraction analysis. The rectangles exhibited multielectron-redox properties. The introduction of a bridging quininone moiety made notable changes in two well-separated single-electron reductions of the bpy moiety, as compared with other 2,2'-bisbenzimidazolate (BiBzlm) or thiolate- or alkoxide-bridged rectangles, followed by quasi-reversible reduction of the quininone moiety to allow the existence of different redox states. Electrochemical assessment using cyclic voltammetry and UV-vis-NIR spectroelectrochemistry revealed reversibly accessible 0, 1-, and 2- redox states. The comproportionation constant of the successive reduction processes was K(c) = 4.18 x 10(8) for complex 1 and 4.08 x 10(8) for 2. In spite of the high K(c) values, no obvious intervalence charge transfer bands were detected in either the vis, NIR, or IR regions, suggesting very weak electronic coupling between the ligand centers in the mixed-valent intermediates. In the mixed-valent intermediate, the overlap between donor and acceptor orbitals of the two bpy ligands engendered weak electronic coupling associated with distance that exceeded van der Waals ligand/ligand distances and created a class I fully isolated, non-interacting, valence-localized situation. Furthermore, unusual ligand-to-metal-to-ligand charge-transfer (LMLCT) transitions of complexes 1 and 2 at 298 K were observed in the visible region. Molecule 2 exhibited multiple emissions from the triplet-centered pi-pi* intraligand ((3)IL), metal-to-ligand charge-transfer ((3)MLCT) and triplet ligand-ligand charge transfer ((3)LLCT) levels and showed biexponential decay. By contrast, in complex 1, (3)IL emission was absent and only single-exponential decay was observed. These results reveal the different nature of the electronically excited states between 1 and 2. The mechanisms of the photophysical deactivation processes in these systems can be explained in terms of the electronic characteristics of the quininone molecules and possible geometrical differences of the excited states involved. In addition, the energies, characteristics, and molecular structures of the ground and lowest triplet excited state were calculated using the density functional theory method.

Design of New n-Type Porphyrin Acceptors with Subtle Side-Chain Engineering for Efficient Nonfullerene Solar Cells with Low Energy Loss and Optoelectronic Response Covering the Near-Infrared Region.

A series of tailor-made highly efficient and near-infrared (NIR) porphyrin-based acceptors is designed and synthesized for fullerene-free bulk-heterojunction (BHJ) organic solar cells. Constructing BHJ active layers using a PTB7-Th donor and porphyrin acceptors (P-x), which have complementary absorption, accomplishes panchromatic photon-to-current conversion from 300 to 950 nm. Our study shows that side chains of the porphyrin acceptors fairly influence the molecular ordering and nanomorphology of the BHJ active layers. Significantly, the porphyrin acceptor with four dodecoxyl side chains (P-2) achieves an open-circuit voltage (VOC) of 0.80 V, short-circuit current density (JSC) of 13.94 mA cm-2, fill factor of 64.8%, and overall power conversion efficiency of 7.23%. This great performance is attributable to the ascendant light-harvesting capability in the visible and near-infrared region, a high-lying LUMO energy level, a relatively high and more balanced carrier mobilities, and more ordered face-on molecular packing, which is beneficial for obtaining high VOC and JSC.

Porphyrin-Containing Polymer as a Superior Blue Light-Absorbing Additive To Afford High- Jsc Ternary Solar Cells.

Integrating an additional component featuring complementary light absorption into binary polymer solar cells is a superior tactic to ameliorate solar cell efficiency and stability. An appropriate additive not only extends the absorption range but may also facilitate charge separation and transport processes. In this work, we elucidate the effects of incorporating a porphyrin-containing conjugated polymer (PPor-1), which displays absorption in 350-500 nm, into binary PTB7-Th:4TIC and PTB7-Th:ITIC blends, affording devices with an average power conversion efficiency approaching 9%. We successfully demonstrate that PPor-1 can be incorporated as an additive to impart improved Jsc (up to 19.1 mA cm-2).

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting.

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current-voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.

Femtosecond fluorescence dynamics of porphyrin in solution and solid films: the effects of aggregation and interfacial electron transfer between porphyrin and TiO2.

The excited-state relaxation dynamics of a synthetic porphyrin, ZnCAPEBPP, in solution, coated on a glass substrate as solid films, mixed with PMMA and coated on a glass substrate as solid films, and sensitized on nanocrystalline TiO2 films were investigated by using femtosecond fluorescence up-conversion spectroscopy with excitation in the Soret band, S2. We found that the S2--> S1 electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs in 910 and 690 fs, respectively, but it becomes extremely rapid, <100 fs, in solid films and TiO2 films due to formation of porphyrin aggregates. When probed in the S1 state of porphyrin, the fluorescence transients of the solid films show a biphasic kinetic feature with the rapid and slow components decaying in 1.9-2.4 and 19-26 ps, respectively. The transients in ZnCAPEBPP/TiO2 films also feature two relaxation processes but they occur on different time scales, 100-300 fs and 0.8-4.1 ps, and contain a small offset. According to the variation of relaxation period as a function of molecular density on a TiO2 surface, we assigned the femtosecond component of the TiO2 films as due to indirect interfacial electron transfer through a phenylethynyl bridge attached to one of four meso positions of the porphyrin ring, and the picosecond component arising from intermolecular energy transfer among porphyrins. The observed variation of aggregate-induced relaxation periods between solid and TiO2 films is due mainly to aggregation of two types: J-type aggregation is dominant in the former case whereas H-type aggregation prevails in the latter case.

Evidence for the assembly of carboxyphenylethynyl zinc porphyrins on nanocrystalline TiO2 surfaces.

UV-visible absorption and AFM studies suggest that carboxyphenylethynyl zinc porphyrins aggregate on nanocrystalline TiO2 surfaces in an H-type fashion.

A VR planning system for craniosynostosis surgery.

The goal of our project is to build a system which could utilize the Virtual Reality (VR) techniques for the pre-operative planning of craniosynostosis. The system includes different modules. We use the tetrahedral volume meshes for the basic structure for the models which surgery is planning on. This paper will describe the procedures of above stages, from the processing of 2D image slices, 3D modeling, smoothing, simplification, and visibility ordering, to volume meshes generation. We have demonstrated the initial results on a variety of stereo devices. The testing results show the processing time is acceptable and the rendering effect is pretty well.

Reductive electropolymerization of N-methyl-3-pyridylethynyl-porphyrins.

Cyclic voltammograms, UV-visible and FT-IR spectra show that porphyrins with two N-methyl-3-pyridylethynyl substituents can undergo reductive electropolymerization on Pt and ITO electrodes. The films are redox active and a mechanism is suggested.

Porphyrin-incorporated 2D D-A polymers with over 8.5% polymer solar cell efficiency.

A copolymerization strategy is developed to utilize porphyrin as a complementary light-harvesting unit (LHU) in D-A polymers. For polymer solar cells (PSCs), the presence of LHUs increases the short-circuit current density (Jsc ) without sacrificing the open-circuit voltage (Voc ) and fill factor (FF). Up to 8.0% power conversion efficiency (PCE) is delivered by PPor-2:PC71 BM single-junction PSCs. A PCE of 8.6% is achieved when a C-PCBSD cathodic interlayer is introduced.

A fluorene-modified porphyrin for efficient dye-sensitized solar cells.

Porphyrins bearing a polyaromatic or a heterocyclic group are prepared to study their fundamental and photovoltaic properties. Solar cells sensitized with a fluorene-modified porphyrin outperform other dyes in the series, reaching ~90% efficiency of N719 dye.

Photoactivation studies of zinc porphyrin-myoglobin system and its application for light-chemical energy conversion.

An artificial zinc porphyrin-myoglobin-based photo-chemical energy conversion system, consisting of ZnPP-Mb or ZnPE(1)-Mb as a photosensitizer, NADP(+) as an electron acceptor, and triethanolamine as an electron donor, has been constructed to mimic photosystem I. The photoirradiated product is able to reduce a single-electron acceptor protein cytochrome c, but cannot catalyze the two-electron reduction of acetaldehyde by alcohol dehydrogenase, thus demonstrating a single electron transfer mechanism. Furthermore, the artificial system can bifunctionally promote oxidoredox reactions, depending on the presence or absence of a sacrificial electron donor, thus suggesting its potential application in electrochemical regeneration steps involved in chemical transformation and/or energy conversion.

A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells.

We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency η = 10.17%.

Preparation, electrochemical and spectral properties of free-base and manganese N-methyl-pyridylethynyl porphyrins.

Two series of free-base and manganese N-methyl-pyridylethynyl-5,15-biphenyl porphyrins were synthesized, and their UV-Visible, electrochemical and spectro-electrochemical properties were studied. Cyclic voltammetry experiments showed positive shifts in the reduction potentials and the UV-Visible spectra showed significant red-shifts in the absorption wavelengths of these porphyrins, indicating the effects of N-methyl-pyridylethynyl substituents.