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Hybrid organic-inorganic perovskites have shown incredible promise as active materials for photovoltaic devices, but their instability to light remains a significant roadblock in realizing these applications. Changing the organic cation has been shown to affect light-induced degradation. As a strategy for increasing the stability of these materials, we replaced varying percentages of methylammonium ion in the archetypical methylammonium lead iodide (MAPbI

Molecular motors have evolved to transduce chemical energy from adenosine triphosphate into mechanical work to drive essential cellular processes, from muscle contraction to vesicular transport. Dysfunction of these motors is a root cause of many pathologies necessitating the need for intrinsic control over molecular motor function. Herein, we demonstrate that positional isomerism can be used as a simple and powerful tool to control the molecular motor of muscle, myosin. Using three isomers of a synthetic non-nucleoside triphosphate we demonstrate that myosin’s force and motion generating capacity can be dramatically altered at both the ensemble and single molecule levels. By correlating our experimental results with computation, we show that each isomer exerts intrinsic control by affecting distinct steps in myosin’s mechano-chemical cycle. Our studies demonstrate that subtle variations in the structure of an abiotic energy source can be used to control the force and motility of myosin without altering myosin’s structure.Statement of SignificanceMolecular motors transduce chemical energy from ATP into the mechanical work inside a cell, powering everything from muscle contraction to vesicular transport. While ATP is the preferred source of energy, there is growing interest in developing alternative sources of energy to gain control over molecular motors. We synthesized a series of synthetic compounds to serve as alternative energy sources for muscle myosin. Myosin was able to use this energy source to generate force and velocity. And by using different isomers of this compound we were able to modulate, and even inhibit, the activity of myosin. This suggests that changing the isomer of the substrate could provide a simple, yet powerful, approach to gain control over molecular motor function.

Conjugated polymers need to be doped to increase charge carrier density and reach the electrical conductivity necessary for electronic and energy applications. While doping increases carrier density, Coulomb interactions between the dopant molecules and the localized carriers are poorly screened, causing broadening and a heavy tail in the electronic density‐of‐states (DOS). The authors examine the effects of dopant‐induced disorder on two complimentary charge transport properties of semiconducting polymers, the Seebeck coefficient and electrical conductivity, and demonstrate a way to mitigate them. Their simulations, based on a modified Gaussian disorder model with Miller‐Abrahams hopping rates, show that dopant‐induced broadening of the DOS negatively impacts the Seebeck coefficient versus electrical conductivity trade‐off curve. Increasing the dielectric permittivity of the polymer mitigates dopant‐carrier Coulomb interactions and improves charge transport, evidenced by simultaneous increases in conductivity and the Seebeck coefficient. They verified this increase experimentally in iodine‐doped P3HT and P3HT blended with barium titanate (BaTiO3) nanoparticles. The addition of 2% w/w BaTiO3 nanoparticles increased conductivity and Seebeck across a broad range of doping, resulting in a fourfold increase in power factor. Thus, these results show a promising path forward to reduce the dopant‐charge carrier Coulomb interactions and mitigate their adverse impact on charge transport., Organic electronic materials must be doped to increase their conductivity, but dopants increase energetic disorder and impede the motion of charge carriers. Here the authors show that the addition of nanoparticles having very high dielectric constants effectively screens the interaction between dopants and charge carriers, resulting in significant improvements in conductivity and the thermoelectric power factor.

Organic-nanoparticle-based solar cells have drawn great attention due to their eco-friendly and environmentally friendly fabrication procedure. However, these surfactant-stabilized nanoparticles suffer open-circuit voltage loss due to charge trapping and poor extraction rate at the polymer cathode interface. Here, we have investigated the origin of voltage loss and charge trapping in surfactant-stabilized nanoparticle-based devices. Efficient organic photovoltaic (OPV) devices have been fabricated from an aqueous dispersion of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C

In this work, we used solvent vapor annealing as a route toward controlled cluster growth of a nitrogen-substituted terrylene molecule (7,8,15,16-tetrazaterrylene or TAT) to probe the underlying molecular packing behind the exciton band curvature (EBC) inversion leading to a so-called HJ aggregates. Using a suite of photoluminescence (PL) imaging tools, we show that the EBC—as signaled by PL spectral signatures—are correlated with distinct polarization and defocused emission patterns suggestive of a high degree of chromophore alignment. Selected area electron diffraction showed that the small aggregates adopt nominally the same crystal packing structure as the extended crystals though with a different plane orientation ([010] vs [011]) with respect to the surface normal. These findings demonstrate experimentally that the EBC inversion is not due to a crystal polymorphism but, rather subtle differences in molecular registration that profoundly impacts interchromophore coupling.

We studied ion transport in hybrid organic–inorganic perovskite p-i-n devices as a function of applied bias under device operating conditions. Using electrochemical impedance spectroscopy (EIS) and equivalent circuit modeling, we elucidated various resistive and capacitive elements in the device. We show that ion migration is predictably influenced by a low applied forward bias, characterized by an increased capacitance at the hole-transporting (HTM) and electron-transporting material (ETM) interfaces, as well as in bulk. However, unlike observations in n-i-p devices, we found that there is a capacitive discharge leading to ion redistribution in the bulk at high forward biases. Furthermore, we show that a chemical double-layer capacitance buildup as a result of ion accumulation impacts the electronic properties of the device, likely by inducing either charge pinning or charge screening, depending on the direction of the ion-induced field. Lastly, we extrapolate ion diffusion coefficients (∼10–7 cm2 s–1) a...

Using photo-Kelvin Probe Force Microscopy (photo-KPFM) we observed macroscopic, photo-induced polarization through 200 nm thick polycrystalline methylammonium lead triiodide (MAPbI3) perovskite films in MAPbI3/charge carrier transport material (CTM) bilayers. A polarization of up to ∼600 mV was observed for some MAPbI3/CTM bilayers and the sign of polarization is dependent on the predominant charge carrier properties of the CTM used. We propose that through-film photo-KPFM polarization measurements can be useful in determining the efficacy of a CTM. Polarized perovskite films may also have applications as surfaces for performing electrochemical reactions.

Energy densities of ~510 J/g (max: 698 J/g) have been achieved in azobenzene-based syndiotactic-rich poly(methacrylate) polymers. The processing solvent and polymer-solvent interactions are important to achieve morphologically optimal structures for high-energy density materials. This work shows that morphological changes of solid-state syndiotactic polymers, driven by different solvent processings play an important role in controlling the activation energy of Z-E isomerization as well as the shape of the DSC exotherm. Thus, this study shows the crucial role of processing solvents and thin film structure in achieving higher energy densities.

Using a methylammonium selective membrane in conjunction with electrochemical impedance spectroscopy, we measured ion migration in methylammonium lead triiodide (MAPbI3) with a millisecond (ms) time constant under illumination. These values were consistent with the reported values of ionic conduction in thin-film perovskite solar cells. We monitored an electrochemical impedance response arising from ionic conductivity through MAPbI3 and a methylammonium selective layer. We could fit this complex impedance response to an intuitive circuit model, which revealed an ionic species moving on a ms time scale. Electrospray ionization mass spectrometry (ESI-MS) revealed direct chemical evidence of methylammonium diffusion into the ion-selective layer. We found no experimental evidence indicating the mobility of lead ions or protons, suggesting that the mobile species observed under illumination is likely methylammonium.

Using impedance spectroscopy and computation, we show that incorporation of multi-walled carbon nanotubes (MWCNTs) in the bulk of the active layer of perovskite-based solar cells reduces charge recombination and increases the open circuit voltage. An ∼87% reduction in recombination was achieved when MWCNTs were introduced in the planar-heterostructure perovskite solar cell containing mixed counterions. The open circuit voltage (Voc) of perovskite/MWCNTs devices was increased by 70 mV, while the short circuit current density (Jsc) and fill factor (FF) remained unchanged.

Binary polymer nanoparticle glasses provide opportunities to realize the facile assembly of disparate components, with control over nanoscale and mesoscale domains, for the development of functional materials. This work demonstrates that tunable electrical percolation can be achieved through semiconducting/insulating polymer nanoparticle glasses by varying the relative percentages of equal-sized nanoparticle constituents of the binary assembly. Using time-of-flight charge carrier mobility measurements and conducting atomic force microscopy, we show that these systems exhibit power law scaling percolation behavior with percolation thresholds of ∼24-30%. We develop a simple resistor network model, which can reproduce the experimental data, and can be used to predict percolation trends in binary polymer nanoparticle glasses. Finally, we analyze the cluster statistics of simulated binary nanoparticle glasses, and characterize them according to their predominant local motifs as (p(i), p(1-i))-connected networks that can be used as a supramolecular toolbox for rational material design based on polymer nanoparticles.

Herein we demonstrate the utility of polyisobutylene (PIB) as a fully printable self-healing sealant for protecting organic photovoltaic devices from degradation under ambient conditions. These sealants can be applied on flexible substrates using drop casting, spin coating or blade coating. PIB-based crosslinked sealants show excellent device stability, especially the low molecular weight PIB.

Herein we demonstrate that efficient perovskite solar cells can be fabricated by a desktop multi-channel inkjet printer. In this approach, different alkyl-ammonium counterions were loaded separately into the printer cartridges and deposited onto PbI2 coated substrates. Structural as well as electronic properties of perovskite solar cells can be tuned by varying the composition ratio of multiple cations in-situ through the RGB color codes of the multi-channel inkjet printer. This roll-to-roll compatible technique provides rapid and facile screening of multiple and mixed counterion perovskite solar cell systems with high reproducibility, potentially leading to possibilities of high-throughput screening technique in future perovskite solar cell fabrication.

Organic materials have attracted recent interest as thermoelectric (TE) converters due to their low cost and ease of fabrication. We examine the effects of disorder on the TE properties of semiconducting polymers based on the Gaussian disorder model (GDM) for site energies while employing Pauli's master equation approach to model hopping between localized sites. Our model is in good agreement with experimental results and a useful tool to study hopping transport. We show that stronger overlap between sites can improve the electrical conductivity without adversely affecting the Seebeck coefficient. We find that positional disorder aids the formation of new conduction paths with an increased probability of carriers in high energy sites leading to a simultaneous increase in electrical conductivity and Seebeck coefficient. On the other hand, energetic disorder leads to increased energy gap between sites, hindering transport, and adversely affects both conductivity and Seebeck. Furthermore, positional correlation primarily affects conductivity, while correlation in energy has no effect on TE properties of polymers. Our results also show that the Lorenz number increases with Seebeck coefficient, largely deviating from the Sommerfeld value, in agreement with experiments and in contrast to band conductors. We conclude that reducing energetic disorder while increasing positional disorder can lead to higher TE power factors., 22 pages, 6 figures, updated figure 3 and expanded the analysis of the new results

A significant challenge in the rational design of organic thermoelectric materials is to realize simultaneously high electrical conductivity and high induced-voltage in response to a thermal gradient, which is represented by the Seebeck coefficient. Conventional wisdom posits that the polymer alone dictates thermoelectric efficiency. Herein, we show that doping — in particular, clustering of dopants within conjugated polymer films — has a profound and predictable influence on their thermoelectric properties. We correlate Seebeck coefficient and electrical conductivity of iodine-doped poly(3-hexylthiophene) and poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl)-alt-(2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)] films with Kelvin probe force microscopy to highlight the role of the spatial distribution of dopants in determining overall charge transport. We fit the experimental data to a phonon-assisted hopping model and found that the distribution of dopants alters the distribution of the density of states and the Kang–Snyder transport parameter. These results highlight the importance of controlling dopant distribution within conjugated polymer films for thermoelectric and other electronic applications., Designing organic thermoelectric materials with high electrical conductivity and Seebeck coefficient is challenging due to the direct relationship between these two properties. Here, the authors explore the role of dopant spatial distribution on thermoelectric performance in conjugated polymers.

Persistent n-doped conjugated polymers were achieved by doping the electron accepting PDNDIV and PFNDIV polymers with ionic (TBACN) or neutral (TDAE) dopants. The great electron affinities, as indicated by the low LUMO levels of PDNDIV (−4.09 eV) and PFNDIV (−4.27 eV), facilitated the chemical reduction from either TBACN or TDAE. The low-lying LUMOs of the neutral polymers PDNDIV and PFNDIV were achieved by incorporation of vinylene spacers between the electron poor NDI units to increase the conjugation length without the use of an electron donor, and this was lowered further by an electron-withdrawing fluorinated N-substituent on the NDI moiety. The polymer radical anions were found to persist for several days under ambient conditions by EPR spectroscopy. A distinguishing and noteworthy feature of these polymers is that they can be consecutively reduced by up to four electrons in acetonitrile. Conductivity measurements demonstrate the prospective impact of PDNDIV and PFNDIV for organic electronics.

We demonstrate that MWCNTs can be dispersed in common organic solvents as single tubes using a single hexabenzocoronene (HBC) unit at the end of a poly(methyl methacrylate) (PMMA) chain. The concentration of the HBC-based additive needed to disperse MWCNTs is substantially lower than the concentration needed for existing additives.

Nanoparticle (NP) assemblies are particularly appealing as active layers of organic photovoltaic (OPV) devices because their aqueous synthesis reduces the usage of chlorinated solvents and because the nanoparticle size, ratio, and internal structure can be controlled precisely. Understanding quantitatively the effects of active layer nanostructure on charge carrier transport in NP-assembly-based OPV devices is crucial in order to optimize device performance. Toward this end, in this study, we report results of numerical simulations of electron and hole transport in OPV devices with active layers consisting of P3HT:PCBM nanoparticle assemblies based on deterministic charge carrier transport models. The models account for the dynamics of bounded electron–hole pairs and free charge carriers, as well as trapped charge carrier kinetics, self-consistently with the electric field distribution in the device active layer. The models reproduce both transient photocurrents from time-of-flight (TOF) experiments and s...

Fabricating macromolecular mesoscale assemblies containing disparate components with targeted molecular order for each of the components on the nanoscale and targeted assembly of the components in the mesoscale is a challenge. In this Perspective, we explore the self-assembly of polymer nanoparticles as a viable route to obtain tunable mesostructured materials. We describe the state-of-the-art methods available for and the challenges to obtain spherical and nonspherical polymer nanoparticles. We discuss the predicted ordered assemblies and disordered assemblies of nanoparticles and the challenges to obtain these assemblies in polymer nanoparticles. We also comment on the rich and future opportunities in the burgeoning field of polymer nanoparticle assemblies.

Hybrid organic–inorganic perovskites (HOIPs) have emerged as an important class of materials because they exhibit many properties suitable for efficient energy conversion and storage. Although HOIPs have been the subject of many studies, the underlying origins of many of their properties remain a matter of debate. Ion transport is a case in point. Even though many in the HOIP research community accept ion transport as the cause of many of HOIPs observed properties, salient details such as the chemical identity of the migrating ion or ions and the mechanism of transport remain unclear. Complicating factors such as the possibility of multiple mobile ions, coupled electronic–ionic transport, instability, and unique organic–inorganic character have led to a range of conclusions and opinions about ion transport in HOIPs. An exponential increase in the number of publications and data in a very short time span have not led to convergence of opinions. In this chapter, we integrate key experimental and computational findings to highlight the fundamental results in the area of ion migration in HOIPs and our current understanding on the nature of ion migration in these materials.

We report numerical simulation results on hole transport in layers of the organic polymer poly(3-hexylthiophene) (P3HT) of different nanostructures based on a deterministic, phenomenological drift–diffusion-reaction model that accounts for hole trapping–detrapping kinetics. The model is used to characterize the various P3HT layers examined in terms of their hole transport dispersivity. The model reproduces well experimental data of photocurrent evolution in P3HT samples ranging from drop cast thin films to surfactant-stabilized nanoparticle assemblies, explains the role of excess surfactant molecules in hole trapping for assemblies of P3HT nanoparticles, and demonstrates quantitatively the potential of using nanoparticle assemblies in organic photovoltaic devices.

For environmentally friendly and cost-effective manufacturing of organic photovoltaic (OPV) cells, it is highly desirable to replace haloarenes with water as the active layer fabrication solvent. Replacing an organic solvent with water requires retooling the device fabrication steps. The optimization studies were conducted using poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as active layer materials. These materials were dispersed in water as blend and separate nanoparticles using the miniemulsion method. Topologies of the active layers were investigated using atomic force microscopy and electron microscopy techniques. We have identified two essential steps to fabricate efficient OPVs from aqueous dispersions: (1) treatment of the hole-transport layer with UV-O3 to make the surface hydrophilic and (2) the use of an electron-transporting buffer layer for efficient charge extraction. We have also identified relative humidity and substrate temperature as key fabrication parameters for obtaining uniform active layer films. The OPV devices were fabricated using PEDOT:PSS as the hole-transport layer and PCBM as electron-transport layer with Ca/Al as the counter electrode. Efficiencies of 2.15% with a fill factor over 66% were obtained; the efficiency and the fill-factor is the highest among all aqueous processing of P3HT–PCBM nanoparticle solar cells.

We observe more than two orders of magnitude enhancement of fluorescence quenching in colloidal conjugated polymer nanoparticles by nitroaromatic analytes compared to solution of the same polymer in organic solvents. This observation is surprising as the quantum efficiency of fluorescence of the polymer solution is significantly higher. The colloidal nanoparticle dispersions of substituted polythiophene derivative are fabricated by the surfactant-assisted mini-emulsion technique. Stern–Volmer constants are determined using both one-photon and two-photon excitation methods. We believe strong analyte–nanoparticle interaction results in the large value of the Stern–Volmer constants measured. The nanoparticle-based sensor described here is suitable for developing a field-based sensory device for detecting a broad class of nitroaromatics in solution.

Perovskite-containing tandem solar cells are attracting attention for their potential to achieve high efficiencies. We demonstrate a series connection of a ∼ 90 nm thick perovskite front subcell and a ∼ 100 nm thick polymer:fullerene blend back subcell that benefits from an efficient graded recombination layer containing a zwitterionic fullerene, silver (Ag), and molybdenum trioxide (MoO3). This methodology eliminates the adverse effects of thermal annealing or chemical treatment that occurs during perovskite fabrication on polymer-based front subcells. The record tandem perovskite/polymer solar cell efficiency of 16.0%, with low hysteresis, is 75% greater than that of the corresponding ∼ 90 nm thick perovskite single-junction device and 65% greater than that of the polymer single-junction device. The high efficiency of this hybrid tandem device, achieved using only a ∼ 90 nm thick perovskite layer, provides an opportunity to substantially reduce the lead content in the device, while maintaining the high performance derived from perovskites.

Nanoparticles derived from π-conjugated polymers have gained widespread attention as active layer materials in various organic electronics applications. The optoelectronic, charge transfer, and charge transport properties of π-conjugated polymers are intimately connected to the polymer aggregate structure. Herein we show that the internal aggregate structure of regioregular poly(3-hexylthiophene) (P3HT) within polymer nanoparticles can be tuned by solvent composition during nanoparticle fabrication through the miniemulsion process. Using absorption spectra and single-NP photoluminescence decay properties, we show that a solvent mixture consisting of a low boiling good solvent and a high boiling marginal solvent results in polymer aggregate structure with a higher degree of uniformity and structural order. We find that the impact of solvent on the nature of P3HT aggregation within nanoparticles is different from what has been reported in thin films.

We report on the single-molecule chiroptical properties of "right"-handed bridged triaryl amine helicene dimers, MH2. Using an experimental setup to precisely define the circular excitation polarization at the sample plane, we investigated the circular dichroic response in luminescence from individual molecules in which induced ellipticity from microscope optics is minimized. Our results comparing circular anisotropies in fluorescence excitation from MH2 and perylene diimide (PDI), an achiral, centrosymmetric chromophore, demonstrate a significant reduction in the breadth of the distribution of circular dissymmetry parameters obtained from modulation of the circularly polarized excitation source (457 nm). For PDI, we observe a symmetric distribution of circular anisotropy parameters centered about zero, with a fwhm of 0.25. For MH2, we observe an asymmetric distribution peaked at g = -0.09, with a slightly larger width as the corresponding PDI distribution. These results indicate that the large dissymmetry parameters (|g|0.5) in fluorescence excitation described in our original report (Hassey, R.; et al. Chirality 2008, 20, 1039-1046 and Hassey, R.; et al. Science 2006, 314, 1437-1439) were indeed affected by (at the time, unknown) linear polarization artifacts. However, the present results on MH2 provide compelling evidence for single-molecule circular dissymmetries much larger than solution or thin-film ensemble values, defined primarily by the enhanced rotatory strength (relative to the monomer), and restricted orientation at the sample surface.

We have modelled structures and dynamics of hydrogen bond networks that form from imidazoles tethered to oligomeric aliphatic backbones in crystalline and glassy phases. We have studied the behaviour of oligomers containing 5 or 10 imidazole groups. These systems have been simulated over the range 100–900 K with constant-pressure molecular dynamics using the AMBER 94 forcefield, which was found to show good agreement with ab initio calculations on hydrogen bond strengths and imidazole rotational barriers. Hypothetical crystalline solids formed from packed 5-mers and 10-mers melt above 600 K, then form glassy solids upon cooling. Viewing hydrogen bond networks as clusters, we gathered statistics on cluster sizes and percolating pathways as a function of temperature, for comparison with the same quantities extracted from neat imidazole liquid. We have found that, at a given temperature, the glass composed of imidazole 5-mers shows the same hydrogen bond mean cluster size as that from the 10-mer glass, and t...

This review focuses on the recent developments in our understanding of active layer morphologies for organic photovoltaic cells and approaches to obtain active layer morphologies for high power conversion efficiencies. The evolution of active layer morphologies, as studied by high resolution electron microscopy, X-ray and neutron scattering, and dynamic secondary ion mass spectrometry, is covered, along with strategies including the use of small molecule additives, polymer nanowires and polymer nanoparticles to realize active layer morphologies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

We have probed the effect of side chains on the charge transfer dynamics in dyads containing quaterthiophene (QT) donor and naphthalene diimide (NDI) acceptor. The donor and the acceptor are covalently linked using a flexible linker. Four dyads (1–4) were synthesized with the quaterthiophene bearing hexyl side chain and the naphthalene diimide bearing hydrocarbon, fluorocarbon, branched or polar side chains. The UV-Vis spectra for these dyads showed the existence of a donor-acceptor complex. The time-resolved fluorescence (TRF) decay studies show a rapid quenching of fluorescence in all the dyads upon excitation of the donor. We found that the side chains on the NDI did not alter the quenching rates in solution.

In this Perspective, we discuss the possibility of constructing binary nanoparticle superlattices for organic photovoltaic applications and some of the interesting new photophysics emerging from preliminary studies. We summarize recent advances in nanoparticle preparation and photophysical characterization and some of the very interesting observed departures from thin-film photoluminescence dynamics. We conclude by discussing some of the challenges ahead and the possibility of new emergent physics in the assembly of polymer nanoparticles into functional devices.

We report on a remarkable size and internal structure dependence on time- and polarization-resolved photoluminescence (PL) from individual regioregular rrP3HT (poly-3-(hexylthiophine)) nanoparticle...

Highly crystalline, continuous parallel arrays of CdSe nanowires have been generated through electrodeposition using photoresist templates. Easy soft imprint nanolithography (ESINL) was used to pattern a commercially available photoresist, Norland Optical Adhesive 60 (NOA 60), deposited onto the ITO substrates, prior to electrodeposition. Using the exposed ITO layer as an electrode, a thin film of CdSe was electrodeposited from an electrolyte containing CdCl2, SeO2, and HCl on the substrate, and the resist was subsequently removed in an alkaline developer solution. The resulting CdSe nanowires were 100 nm in thickness, 300–500 nm in width, and several centimeters in length. Imprinted templates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDX). The SEM analysis confirmed the formation of parallel arrays of nanowires unaffected by the resist lift-...

We have modeled structures and energetics of anhydrous proton-conducting wires: tethered hydrogen-bonded chains of the form ···HX···HX···HX···, with functional groups HX = imidazole, triazole, and formamidine; formic, sulfonic, and phosphonic acids. We have applied density functional theory (DFT) to model proton wires up to 19 units long, where each proton carrier is linked to an effective backbone to mimic polymer tethering. This approach allows the direct calculation of hydrogen bond strengths. The proton wires were found to be stabilized by strong hydrogen bonds (up to 50 kJ/mol) whose strength correlates with the proton affinity of HX [related to pK(b)(HX)] and not to pK(a)(HX) as is often assumed. Geometry optimizations and ab initio molecular dynamics near 400 K on imidazole-based proton wires both predict that adding a proton to the end of such wires causes the excess charge to embed into the interior segments of these wires. Proton translocation energy landscapes for imidazole-based wires are sensitive to the imidazole attachment point (head or feet) and to wire architecture (linear or interdigitated). Linear imidazole wires with head-attachment exhibit low barriers for intrawire proton motion, rivaling proton diffusion in liquid imidazole. Excess charge relaxation from the edge of wires is found to be dominated by long-range Grotthuss shuttling for distances as long as 42 Å, especially for interdigitated wires. For imidazole, we predict that proton translocation is controlled by the energetics of desorption from the proton wire, even for relatively long wires (600 imidazole units). Proton desorption energies show no correlation with functional group properties, suggesting that proton desorption is a collective process in proton wires.

π-Conjugated moieties are often attached to conjugated polymers to systematically alter their electronic properties. Herein, we report the synthesis and properties of a thiophene polymer bearing a triazole moiety in the third position. Through NMR-based quenching studies, we show that the placement of the triazole moiety alters reaction pathway of the Ni(0)-mediated Grignard metathesis polymerization possibly through chelation. When compared with a triazole on the main chain, the pendant triazole moiety acts as an electron donor and lowers the band gap of the polymer. The triazole moiety also does not hinder the packing of the conjugated backbone. We also show that the fluorescence of this polymer is quenched with PCBM, indicating its potential as a candidate for organic photovoltaic devices.

What are the stumbling blocks for achieving high-efficiency organic photovoltaic devices? This question is examined from a molecular architecture and molecular packing perspective. The intermolecular interaction between the electron donor and electron acceptor influences the charge separation. The packing of electron donors and acceptors influences the charge transport. Therefore, there is a need to strike a balance between the charge-transfer interactions and packing interactions and obtain nanoscale segregated morphologies for efficient charge separation and charge transport. Molecular architecture is key toward striking this balance and, therefore, its impact on charge-transfer interactions and packing interactions; thus, the active-layer morphology and photovoltaic metrics are examined. A variety of molecular architectures for the packing of π-conjugated organic molecules to structures relevant for photovoltaic devices is also discussed.

The hydroboration of phenyl vinyl sulfide with catecholborane (HBcat) and pinacolborane (HBpin) has been examined with a number of rhodium complexes, all of which proceed with excellent regiocontrol in favour of the branched product PhSCH(B(OR)2)CH3. The corresponding linear product can be obtained exclusively in reactions employing [Cp*IrCl2]2 and HBcat. Catalysed hydroborations of (E)-2-(p-toluenethio)styrene with HBcat using Rh(acac)(dppp) gave predominant formation of one product while reactions using HBpin afforded several products arising from a competing C–S bond cleavage (acac = acetylacetonato, dppp = 1,3-bis(diphenylphosphino)propane). Although reactions of phenyl vinyl sulfoxide were complicated by a competing deoxygenation reaction, hydroborations of phenyl vinyl sulfone using HBcat once again gave regioselective formation of either the branched or linear products, depending on the choice of catalyst used to effect this transformation. Catalysed hydroborations of phenyl vinyl sulfonate were less chemo- and regioselective, yielding hydrogenation and diboration products in addition to the two hydroboration product isomers. © 2007 Elsevier B.V. All rights reserved.

Nanoporous polymer thin films produced from ordered block copolymer precursors have received considerable attention, because they can be used in many applications including templating, separation, catalysis, and sensors. Since 1988, various block copolymers have been used to prepare nanoporous thin films via the selective removal of degradable minor components from self-assembled block copolymers. For cylinder-forming block copolymers, selective etching of the cylindrical microdomain in an ordered block copolymer results in the formation of nanoscopic channels. Specially, if the etchable cylinders are orientated normal to the film surface, removal of the cylinders will lead to the nanolithographic masks used in block-copolymer lithography. Currently, the generation of nanoporous materials from ordered block copolymers relies on a selective etching protocol that does not compromise the integrity of the matrix material. Ozonolysis, UV degradation, reactive ion etching (RIE), and chemical etching are the methods that are commonly used for the removal of minor components to create nanopores. However, the number of polymers that can be degraded under mild reaction conditions in the thin-film state is limited. The preparation of nanoporous thin films from block copolymers without a degradable component requires a rational design of the polymer. In principle, to generate nanopores from self-assembled block copolymers, it is not necessary to degrade the backbone bonds in the minor component; rather, a cleavage of the juncture between two immiscible blocks is sufficient. Therefore, if one could put a cleavable juncture into a block copolymer; the cleavage will not depend on the chemical nature of the minor component and should be applicable to a much larger variety of block copolymers. Cleavage of the juncture point of block copolymer in the ordered state followed by removal of the minor component via selective solvents is therefore a very promising strategy for the generation of nanoporous structures. For most of the nanoporous polymer thin films prepared to date, one of the major problems is the lack of long-range order in the nanopore array, which prevents them from being used in applications where addressability is required (e.g., magnetic storage devices). Long-range order in thin films of the precursor block copolymers is a prerequisite for obtaining nanoporous materials with well-ordered pores. We have recently demonstrated that the solvent-annealing of thin films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers leads to highly ordered arrays of PEO cylinders oriented normal to the film surface. The long-range lateral order and the orientation in the annealed PS-b-PEO thin films arise from the strong nonfavorable interactions between PS and PEO, enhanced mobility caused by the presence of solvent, as well as the directionality of solvent evaporation. The subsequent removal of the PEO domain will lead to nanoporous films with identical long-range order. However, the poor degradability of PEO prevents the direct generation of nanopores from ordinary PS-b-PEO. Mao and Hillmyer recently reported the successful use of hydroiodic acid to degrade PEO in the bulk sample of PS-b-PEO, but the harsh reaction conditions they used are not applicable to thin films. To impart the degradability to the PS-b-PEO system, we recently synthesized a triblock copolymer, polystyrene-bpoly(methyl methacrylate)-b-poly(ethylene oxide) (PS-bPMMA-b-PEO), where PS is the major component and PMMA and PEO are minor components. By taking the advantage of the photodegradability of the PMMA mid-block, nanoporous thin films with excellent long-range order suitable for block copolymer lithography were prepared. In this method, the degradation efficiency depends critically on the molecular weight and phase behavior of the PMMA block, and only when PMMA formed a distinct microdomain did efficient degradation occur. In this paper, we show that by placing a cleavable juncture, a triphenylmethyl (trityl) ether linkage, between PS and PEO, C O M M U N IC A IO N

Solar cells fabricated using alkyl ammonium metal halides as light absorbers have the right combination of high power conversion efficiency and ease of fabrication to realize inexpensive but efficient thin film solar cells. However, they degrade under prolonged exposure to sunlight. Herein, we show that this degradation is quasi-reversible, and that it can be greatly lessened by simple modifications of the solar cell operating conditions. We studied perovskite devices using electrochemical impedance spectroscopy (EIS) with methylammonium (MA)-, formamidinium (FA)-, and MA(x)FA(1-x) lead triiodide as active layers. From variable temperature EIS studies, we found that the diffusion coefficient using MA ions was greater than when using FA ions. Structural studies using powder X-ray diffraction (PXRD) show that for MAPbI3 a structural change and lattice expansion occurs at device operating temperatures. On the basis of EIS and PXRD studies, we postulate that in MAPbI3 the predominant mechanism of accelerated device degradation under sunlight involves thermally activated fast ion transport coupled with a lattice-expanding phase transition, both of which are facilitated by absorption of the infrared component of the solar spectrum. Using these findings, we show that the devices show greatly improved operation lifetimes and stability under white-light emitting diodes, or under a solar simulator with an infrared cutoff filter or with cooling.

Solar cells constructed of organic materials are becoming increasingly efficient due to the discovery of the bulk heterojunction concept. This review provides an overview of organic solar cells. Topics covered include: a brief history of organic solar cell development; device construction, definitions, and characteristics; and heterojunction morphology and its relation to device efficiency in conjugated polymer/fullerene systems. The aim of this article is to show that researchers are developing a better understanding of how material structure relates to function and that they are applying this knowledge to build more efficient light-harvesting devices.

A two-term model is proposed for hydrocarbon and N-containing pi-radicals which are in close contact with one another. The first term is attractive (due to partially occupied frontier pi-orbitals), and the second, repulsive (due to hard-core repulsion between close-lying atoms). This model is applied to dimers where intermolecular contacts are closer than0.95 x the sum of the atomic van der Waals radii. The maximin principle is proposed. The maximin principle states that the lowest energy conformation maximizes overlap of the frontier orbitals while simultaneously minimizing intermolecular contacts. A Hückel Hamiltonian, the mu(2)-Hamiltonian, which contains the above attractive and repulsive terms, is applied. The interaction surfaces of two pi-hydrocarbon radical cations were calculated for the three systems known crystallographically to contain cations in close contact: naphthalene, fluoranthene, and pyrene. The global minima of these surfaces correspond to the experimentally determined structures. The mu(2)-Hamiltonian energy surfaces of the naphthalene cation dimer are qualitatively similar to those calculated at the RHF/6-311G(d,p) and MP2/6-311G(d,p) levels. The maximin principle is applied to N-containing pi-radicals. Except in the case of tetracyanoethene, the maximin principle correctly predicts the most common dimer crystal packing. (MgPc)(NO(3)).0.5THF and (MgPc)(ReO(4)).1.5THF (Pc = phthalocyanine) were prepared: both new crystal structures follow the maximin principle. The maximin principle is used to suggest the dimer cation ground state of oligoacenes, cations important as organic hole-based semiconductors.

Synthetic protocols using copper(I) catalysts for the for- mation of diaryl acetylenes, 1,3-enynes, benzofurans and indoles are described. The acetylenic moiety is an important unit found in many compounds that are of pharmaceutical, biological and ma- terial interests. 1 Aryl acetylenes are constituent units in important conjugated polymers. 1c 1,3-Enynes are found in many biologically and pharmaceutically interesting com- pounds. Compounds containing carbon-acetylene bonds are intermediates for the synthesis of heterocycles. For ex- ample, 2-arylethynylphenols are intermediates for the synthesis of 2-arylbenzo(b)furans whereas 2-arylethynyl- anilines are intermediates for the synthesis of 2-arylin- doles; benzofurans and indoles are prevalent in many compounds and natural products that have important bio

A chiral Zn(II)–salen complex tethered with poly(ethylene glycol) (PEG) was synthesized. This soluble polymer-supported complex was found to catalyze the asymmetric addition of diethylzinc to a series of aromatic aldehydes in good yields and with good enantiomeric ratio (er). The PEG-supported catalyst could be recycled and reused up to three times. The reactivity and selectivity of the catalyst was dependent on the nature of the linker between the polymer and the complex.