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Nanoscale patterning of inorganics is crucial for the fabrication of advanced electronic, photonic, and energy devices. The emerging sequential infiltration synthesis (SIS) method fabricates nanofeatures by block-selective vapor-phase growth in block copolymer templates with tunable patterns. Yet, SIS has been demonstrated mainly for Al2O3 and a few other metal oxides, while deriving metal nanostructures from a single SIS process is a challenge. Here, we present SIS of the Ru metal in polystyrene-block-polymethyl methacrylate (PS-b-PMMA) templates without any pretreatment, using alternating infiltration of RuO4 and H-2. RuO4 interacts selectively and strongly with the aromatic C=C and C-H groups in PS, leaving the PMMA domains inert. Density functional theory calculations corroborate that the PS-RuO4 interaction is energetically favorable, with a calculated interaction energy of -1.65 eV, whereas for PMMA-RuO4, the calculated energy of -0.05 eV indicates an unfavorable interaction. Morphological analysis on the di-BCP after the RuO4-H-2 process indicates an increase in contrast as a function of SIS cycles and templated Ru incorporation. The crystalline nature of the Ru deposits is confirmed using grazing incidence wide-angle X-ray scattering. Plasma-aided removal of the organic components yields Ru nanolines with lateral dimensions of ca 20 nm. We further highlight the broad potential of RuO4 as a reactant for SIS by generating RuO2 nanopatterns via alternating RuO4 and methanol infiltration.

Printed electrical gas sensors are a low-cost, lightweight, low-power, and potentially disposable alternative to gas sensors manufactured using conventional methods such as photolithography, etching, and chemical vapor deposition. The growing interest in Internet-of-Things, smart homes, wearable devices, and point-of-need sensors has been the main driver fueling the development of new classes of printed electrical gas sensors. In this Perspective, we provide an insight into the current research related to printed electrical gas sensors including materials, methods of fabrication, and applications in monitoring food quality, air quality, diagnosis of diseases, and detection of hazardous gases. We further describe the challenges and future opportunities for this emerging technology.

Porous carbon films, attributed to their superior thermal and chemical robustness, are attractive for a number of applications. In the context of molecular separation, a major focus has been on films where the effective pore diameter is lower than 1 nm, e.g., carbon molecular sieves. Only a handful of reports are available on carbon films hosting 2-3 nm size pore channels where gas transport mainly takes place by Knudsen diffusion in contrast to activated transport. Recently, we reported nanoporous carbon (NPC) films, by the pyrolysis of phase-separated blockcopolymer/turanose films, as a gas-permeable mechanical reinforcement for crack-free synthesis of single-layer graphene membranes. However, a dedicated study on the nanostructure and transport properties of the standalone NPC film has been missing. Herein, we show that the NPC film has a perforated lamellar (PL) nanostructure where molecular transport is limited by an interlamellar spacing of similar to 2 nm. The unique PL nanostructure of the NPC film originates from its precursor, i.e., a block-copolymer stabilized by hydrogen bonding with a carbohydrate additive, where the latter also acts as the main carbon-forming agent. This nanostructure is highly sensitive to the carbohydrate/block-copolymer ratio and gives way to a lacey structure below a ratio of 2:1. The transport of gases through the interlamellar spacing takes place predominantly in the Knudsen regime, determined by their molecular mass. Attributed to a thickness of 100 nm, the film yields extremely rapid gas transport with a H-2 permeance over two million gas permeation units (GPU) and H-2/CO2 selectivity over 4.5 in a temperature range of 25-300 degrees C. These properties make the NPC film a promising membrane support and a good choice for the mechanical reinforcement for high-permeance twodimensional membranes for gas separation.

Wrinkling instabilities in polymeric bilayers have been exploited as optical phase gratings with tunable performance. Here, we report strain modulated 1D and 2D phase gratings fabricated by the ubiquitous process of plasma-oxidation of polydimethylsiloxane (PDMS). While surface oxidation provides a remarkably facile glassy skin formation approach, minimizing delamination and debonding, it inherently results in a gradient conversion profile emanating from the top film interface. We examine and quantitatively model the consequences of this gradient layer on the optical properties of the resulting strain-tunable phase gratings. Diffraction efficiencies up to 48% are demonstrated. We then develop and validate a surface reconstruction methodology based on the diffraction pattern of our sinusoidal gratings and our model, which we extend to the high deformation regimes and to 2D gratings, obtained by superposition of two wrinkling generations, where both amplitudes and wavelengths can be independently tuned. Overall, this approach provides a rapid, robust and predictive framework for the design and fabrication of tunable, single, and multiaxial surface gratings.

Superhydrophobic surfaces are important parts of many applications in cleaning and protective coatings. Such surfaces can be realized by controlling the surface chemistry and nanoscale structure. Elongated ZnO nanostructures, called nanowires, are often used in superhydrophobic applications due to their intrinsic characteristic advantages and simple synthesis control. This review presents a critical overview of the latest research activities focused on the ZnO nanowire superhydrophobic surfaces. A wettability mechanism background is introduced with the overlay of the crystal structure fundamentals adapted for ZnO nanowires to gain insights into the multifunction application of superhydrophobic ZnO nanowires. Moreover, the latest achievements in application of ZnO superhydrophobic nanowires or reversible wettability for self-cleaning, separation, antifogging, antibacterial, and other applications are outlined. Finally, a brief outlook on the issues and emerging perspectives of ZnO nanowire wettability research is summarized. Keywords

The physicochemical nature of the change in the effective work function (EWF) of aluminum doped TiN (using TiN/TiAl/TiN laminate structure) was studied by X-ray photoelectron spectroscopy with high...

Novel area-selective molecular layer deposition (AS-MLD) of polyimide (PI) on Cu versus native SiO2 was studied. By use of 1,6-diaminohexane (DAH) and pyromellitic dianhydride (PMDA) as precursors, PI films can be selectively deposited on the Cu surface at 200-210 degrees C with a rate around 7.8 A/cycle while negligible growth takes place on SiO2. The selectivity was successfully demonstrated also on Cu/SiO2 patterns at 200 degrees C; after 180 MLD cycles, around 140 nm thick PI was deposited on Cu regions while

When imaged by scanning tunneling microscopy (STM) at constant current under nontopographic conditions, nanosized MgO islands grown on Ag(100) may show a fractal dark internal structure and/or appear embedded in the surface. On the contrary, when imaged under topographic conditions, the same islands appear as nearly flat plateaus. Islands showing different contrast and a different contrast dependence on sample bias have been often reported in the literature, but a thorough explanation is still missing. Here we demonstrate, on the basis of of experimental data and computational results, that such structure is due to the accumulation of oxygen at the MgO islands-substrate interface. Interestingly, interfacial oxygen concentrates at the center of the islands.

Searching for novel materials and controlling their nanostructuration into electronic devices is a challenging task ahead of chemists and chemical engineers. Even more so when this new application requires an exquisite control over the morphology, crystallinity, roughness and orientation of the films produced. In this context, it is of critical importance to analyze the influence of the chemical composition of perspective materials on their properties at the nanoscale. We report the fabrication of ultrathin films (thickness < 30 nm) of a family of FeII Hofmann-like coordination polymers by using an optimized liquid phase epitaxy (LPE) set-up. The series [Fe(L)2{Pt(CN)4}] (L = pyridine, pyrimidine and isoquinoline) conform an ideal platform for correlating the effect of the axial nitrogenated ligand with changes to their structural response to guests or electrical resistance. All film properties relevant to device integration have been thoroughly analyzed with complementary surface techniques for a meaningful comparison. Our results reveal that changes to this ligand can hinder the structural transformation triggered by the absorption of guest molecules previously reported for the pyridine phase. Also important, it can substantially hinder vertical charge transport across the layers, even at the ultrathin film limit.

The structural phase behavior of high-quality single crystals of methylammonium lead iodide (CH3NH3PbI3 or MAPbI3) was revisited by combining Raman scattering and photoluminescence (PL) measurements under high hydrostatic pressure up to ca. 10 GPa. The single crystals were specially grown with the final thickness needed for pressure experiments, retaining their high quality due to a less invasive preparation procedure, which avoids sample thinning. Both PL and Raman spectra show simultaneous changes in their profiles that indicate the occurrence of three phase transitions subsequently at around 0.4, 2.7, and 3.3 GPa. At the second phase transition, the Raman spectra exhibit a pronounced reduction in the line width of the phonon modes of the inorganic cage, similar to the changes observed at the tetragonal-to-orthorhombic phase transition occurring at around 160 K but ambient pressure. This behavior is interpreted as evidence for the locking of the organic cations in the cage voids above 2.7 GPa due to the reduced volume and symmetry of the unit cell. At the third phase transition, reported here for the first time, the PL is greatly affected, whereas the Raman spectrum experiences only subtle changes related to a splitting of some of the peaks. This behavior may indicate a change mostly in the electronic structure with little effect on the crystal structure. Strikingly, the sharp Raman features observed at high pressures do not support amorphization of MAPbI3 with onset at 3 GPa, as claimed by most of the high-pressure (X-ray) literature. We interpret this apparent discrepancy in terms of the degree of disorder introduced at different length scales in the perovskite lattice by the pressure-induced freeze-out of the methylammonium cation motion., The Spanish Ministerio de Economí a, Industria y Competitividad, is gratefully acknowledged for its support through Grant No. SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence program and through Grants MAT2015-70850-P (HIBRI2) and CSD2010-00044 (Consolider NANOTHERM). A.F.-L. acknowledges a FPI fellowship from the Spanish Ministerio co-financed by the European Social Fund. B.C. and O.J.W. thank the EPSRC for Ph.D. studentship funding via the CSCT CDT (EP/ G03768X/1, EP/L016354/1). Financial support is also acknowledged from the European Research Council through project ERC CoG648901.

Lead halide perovskites are mixed electron–ion conductors that support high rates of solid-state ion transport at room temperature, in addition to conventional electron and hole conduction. Mass transport mediated by charged defects is responsible for unusual phenomena such as current–voltage hysteresis in photovoltaic devices, anomalous above-bandgap photovoltages, light-induced lattice expansion and phase separation, self-healing, and rapid chemical conversion between halides. We outline the principles that govern ion transport in perovskite solar cells including intrinsic (point and extended defects) and extrinsic (light, heat, electrical fields, and chemical gradients) factors. These microscopic processes underpin a wide range of reported observations, including photoionic conductivity, and offer valuable directions for both limiting ion transport, where required, and harnessing it to enable new functionality.

One major advantage of organic electronics is their superior processability relative to traditional silicon-based materials. However, most high-performing polymer semiconductors exhibit poor solubility and require toxic chlorinated solvents coupled with inefficient coating methods such as spin-coating for device fabrication. Therefore, developing polymer semiconductors that are processable in environmentally benign solvents and compatible with effective printing techniques while maintaining good charge transport properties is crucial for the industrialization of low-cost and lightweight plastic electronics. In this study, alkyl flexible linkers with branched tertiary carbon atoms are inserted to a high-mobility diketopyrrolopyrrole-based polymer backbone to suppress polymer aggregation in solution, decrease crystallinity, and increase free volume. The polymer readily dissolves in industrial solvents and shows a 70-fold increase in solubility compared to its fully conjugated counterpart. Furthermore, due t...

Composite polymer films incorporating luminescent copper nanoclusters are conveniently fabricated by solution processing of a precursor mixture of polyvinylpyrrolidone, poly(vinyl alcohol), a Cu2+ salt, and glutathione in water. The formation of Cu nanoclusters takes place through chemical reactions of the precursors in a hydrogel network, whose dehydration during the subsequent aging process leads to aggregation-induced emission enhancement. Large-area (25 cm × 32 cm), flexible, transparent, thermally stable, bright-orange-emitting films are realized, with the photoluminescence quantum yield reaching 30%. The emission of the films is attributed to a phosphorescence mechanism, taking place through ligand-to-metal charge transfer followed by a radiative relaxation over a triplet state. Cu-nanocluster-based composite films are employed as a light-emitting layer for down-conversion orange light-emitting diodes. Refereed/Peer-reviewed

International audience; Although TiO2, ZrO2, and HfO2 nanocrystals are often synthesized in tri-n-octylphosphine oxide (TOPO), it is unclear whether TOPO also serves as ligand. Using liquid and solid state 1H and 31P nuclear magnetic resonance spectroscopy and X-ray fluorescence spectroscopy, we show that the nanocrystal surface is capped by several derivatives of TOPO. In the 31P NMR spectrum, di-n-octylphosphinate (δ = 57 ppm) and P,P′-(di-n-octyl) pyrophosphonate (δ = 20 ppm) are found coordinated to the nanocrystal. In addition, hydrogen chloride associates with the metal oxide nanocrystal surface and protonates TOPO. The resulting hydroxyl-tri-n-octylphosphonium, [HO-PR3]+, is tightly associated with the nanocrystal surface (δ(31P) = 73 ppm) due to electrostatic interactions and hydrogen bonding. To simplify the complex surface composition, we exchange the original surface species for carboxylate or phosphonate ligands. The protonation of TOPO is an unexpected example of lyophilic ion pairing between an acidic metal oxide nanocrystal and a weakly basic ligand molecule that is formed in nonpolar solution. Our results contrast with the classically envisaged L-type binding motif of TOPO to surface metal ions. The generality of this stabilization mode and its relevance to catalysis is discussed.

The performance of organic photovoltaic blend devices is critically dependent on the polymer:fullerene interface. These interfaces are expected to impact the structural and thermal properties of the polymer with regards to the conjugated backbone planarity and transition temperatures during annealing/cooling processes. Here, we report the impact of fullerene intercalation on structural and thermal properties of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT), a highly stable material known to exhibit liquid crystalline behavior. We undertake a detailed systematic study of the extent of intercalation in the PBTTT:fullerene blend, considering the use of four different fullerene derivatives and also varying the loading ratios. Resonant Raman spectroscopy allows direct observation of the interface morphology in situ during controlled heating and cooling. We find that small fullerene molecules readily intercalate into PBTTT crystallites, resulting in a planarization of the polymer backbone, but high fullerene loading ratios or larger fullerenes result in nonintercalated domains. During cooling from melt, nonintercalated blend films are found to return to their original morphology and reproduce all thermal transitions on cooling with minimal hysteresis. Intercalated blend films show significant hysteresis on cooling due to the crystallized fullerene attempting to reintercalate. The strongest hysteresis is for intercalated blend films with excess fullerene loading ratio, which form a distinct nanoribbon morphology and exhibit a reduced geminate recombination rate. These results reveal that careful consideration should be taken during device fabrication, as postdeposition thermal treatments significantly impact the charge generation and recombination dynamics.

Polycrystalline diamond films (similar to 10 mu m thick) were grown on five different silicon (Si) substrate orientations by microwave plasma chemical vapor deposition. The selected Si substrates had a range of f(theta): 0.18-0.65. It is to be noted that f(theta) scales inversely with the packing density of the interface. As f(theta) decreased, three changes in the polycrystalline diamond microstructures were observed. (i) At the film surface -fiber texture increased but -fiber dropped. (ii) A novel reconstruction technique was proposed and tested for faceted microstructures. The reconstructed microstructures revealed that the observed texture changes, with a decrease in f(theta), was accompanied by elimination of very fine facets. (iii) Noticeable differences in Raman estimated stress gradients were also observed: the lowest stress gradients for more closed packed substrates.

As-cast and slowly crystallized films of conjugated, polymers can contain (partially) ordered and less ordered (amorphous) regions with structural defects. Crystallization allows to generate chains with highly planarized backbones, embedded in structures exhibiting long-range order. In the present study, we used spatially resolved optical spectroscopy to quantify differences in the degree of order of a bulky substituted poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT). In particular,, we compared absorption and photoluminescence (PL) measurements from large spherulitic crystals, and the same region rapidly recrystallized after melting, which allowed to identify characteristic features of ordered and less ordered regions. In addition, on the basis of temperature-dependent absorbance and PL measurements, we followed in situ melting and recrystallization processes, i.e., transitions between ordered and disordered phases. A multipeak analysis of absorption and PL spectra based on a modified Franck-Condon progression showed changes in for example the relative intensities of each peak, the excitonic bandwidth, and the vibronic energy as a function of temperature. Most importantly; at the phase transition temperature, a clear change in the positions of the peaks (i.e., their wavelengths, corresponding to the energy of the emitted photons) was detected. In particular, the relative absorption and PL intensities depended sensitively on the extent of order within PDOPT samples. Furthermore, on the basis of a comparison with calorimetric measurements, we have confirmed correlations between changes in the relative absorbance and PL intensities with variations in order/disorder occurring during melting and recrystallization.

Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime. Therefore, we present here an innovative exploration, of the crystallization kinetics of Ge2Sb2Te5 (GST) nanoparticles (NPs) exploiting differential scanning calorimetry with ultrafast heating up to 40 000 K s(-1). Our results demonstrate that the non-Arrhenius thermal dependence of viscosity at high temperature becomes an Arrhenius-like behavior when the glass transition is approached, indicating a fragile-to-strong (FS) crossover in the as-deposited amorphous GST NPs. The overall crystal growth rate of the GST NPs is unraveled as well. This unique feature of the FS crossover is favorable for memory applications as it is correlated to improved data retention. Furthermore, we show that methane incorporation during NP production enhances the stability of the amorphous NP phase (and thereby data retention), while a comparable maximum crystal growth rate is still observed. These results offer deep 'insight into the crystallization kinetics of nanostructured GST, paving the way for designing nonvolatile memories with PCM dimensions smaller than 20 nm.

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response., J.M. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant, agreement No. 654682. A.A. and A.I. acknowledge financial support from the Spanish Ministry Ministerio de Economia y Competitividad (MINECO) (code: MAT2015-63704-P (MINECO/FEDER, UE)) and the Eusko Jaurlaritza (Basque Government) (code: IT-654-13). A.C. would like to acknowledge the financial support of the EPSRC (EP/M014142/1). A.N., T.A.E., and C.M. acknowledge financial support from MINECO (codes: MAT2014-59187-R, MAT2015-66443-C02-1-R, and MAT2014-53437-C2-1P, respectively). N.S. is in addition grateful for support from a European Research Council ERC Starting Independent Research Fellowship under the grant agreement No. 279587.

Polycrystalline diamond films were synthesized, by microwave plasma chemical vapor deposition. Films were mechanically stable until 30 mu m thickness, while further deposition led to catastrophic film delamination and rupture. This coincided with fracture of the single-crystal silicon substrate, creating polycrystalline silicon with clear shear markings. Films grown to 12, 18, 21, and 30 mu m were subjected to detailed investigations. Larger film thickness modified intrinsic stresses (estimated from Raman shift) from mildly compressive to strongly tensile. However, normal in-plane residual stresses and dislocation densities, as estimated from X-ray diffraction, dropped. Film growth enhanced anisotropies in crystallographic texture brought changes to grain morphology and significantly increased out-of-plane residual shear stress. Though different models of film delamination/rupture were deliberated, they fail to assimilate all aspects of experimental observations. Shear anisotropy-induced lateral stresses, on the other hand, can explain film rupture and relate the same with substrate/film microstructural developments.

Low intrinsic toxicity, high solubility, and stability are important and necessary features of gold nanoparticles to be used in the biomedical field. In this context, charged nanoparticles proved to be very versatile, and among them charged mixed-monolayer gold nanoparticles, displaying monolayers with well-defined morphologies, represent a paradigm. By using mixtures of hydrogenated and fluorinated thiols, the formation of monolayer domains may be brought to an extreme because of the immiscibility of fluorinated and hydrogenated chains. Following this rationale, mixed monolayer gold nanoparticles featuring ammonium, sulfonate, or carboxylic groups on their surface were prepared by using amphiphilic hydrogenated thiols and 1H,1H,2H,2H-perfluoro-alkanethiols. The toxicity of these systems was assessed in HeLa cells and was found to be, in general, low even for the cationic nanoparticles which usually show a high cytotoxicity and is comparable to that of homoligand gold nanoparticles displaying amphiphilic-charge neutral-hydrogenated or fluorinated thiolates in their monolayer. These properties make the mixed ligand monolayer gold nanoparticles an interesting new candidate for medical application.

International audience; A combined X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the adsorbate interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 × 1 surface. Large molecule–substrate adsorption energies are computed and are found to compete with the molecule–molecule interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.

Copper(I) iodide (CuI) thin films are employed as a structural templating layer for the growth of metal-free phthalocyanine (H2Pc) thin films. Structural polymorphs are observed in X-ray diffraction patterns when microcrystalline CuI films exhibiting copper and iodine terminated grains are used. Each polymorph is nucleated from a single termination, and distinctive crystallite morphologies are observed for each.\ud

This work reports on the unprecedented magnetron sputtering deposition of submicrometric hollow cones of bioactive glass at low temperature in the absence of any template or catalyst. The influence of sputtering conditions on the formation and development of bioglass cones was studied. It was shown that larger populations of well-developed cones could be achieved by increasing the argon sputtering pressure. A mechanism describing the growth of bioglass hollow cones is presented, offering the links for process control and reproducibility of the cone features. The composition, structure, and morphology of the as-synthesized hollow cones were investigated by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), grazing incidence geometry X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)-selected area electron diffraction (SAED). The in vitro biological performance, assessed by degradation tests (ISO 10993-14) and cytocompatibility assays (ISO 10993-5) in endothelial cell cultures, was excellent. This allied with resorbability and the unique morphological features make the submicrometer hollow cones interesting candidate material devices for focal transitory permeabilization of the blood-brain barrier in the treatment of carcinoma and neurodegenerative disorders.

International audience; Precession electron diffraction has been used to provide accurate deformation maps of a device structure showing that this technique can provide a spatial resolution of better than 2 nm and a precision of better than 0.02%. The deformation maps have been fitted to simulations that account for thin specimen relaxation. By combining the experimental deformation maps and simulations, we have been able to separate the effects of the stressor and recessed sources and drains and show that the Si3N4 stressor increases the in-plane deformation in the silicon channel from 0.92 to 1.52 +/- 0.02%. In addition, the stress in the deposited Si3N4 film has been calculated from the simulations, which is an important parameter for device design.

Fast photoswitching of wetting properties is important for the development of micro/nanofluidic systems and lab-on-a-chip devices. Here, we show how structuring the surface amplifies photoswitching properties. Atomic layer-deposited titanium dioxide (TiO2) has phototunable hydrophilic properties due to its surface chemistry, but microscale overhang pillars and additional nanoscale topography can override the chemistry and make the surface superhydrophobic. Three switching processes are achieved simply by controlling the UV exposure time: from (1) rolling superhydrophobic to sticky superhydrophobic (Cassie-Baxter to Wenzel), (2) superhydrophobic to hydrophilic, and (3) superhydrophobic to superhydrophilic after 1, 5, and 10 min of UV exposure, respectively. We report the fastest reversible switching to date: 1 min of UV exposure is enough to promote a rolling-to-sticky transition, and mild heating (30 min at 60 °C) is sufficient for recovery. This performance is caused by a combination of the photoswitching properties of TiO2, the micropillar overhang geometry, and surface nanostructuring. We demonstrate that the switching also can be performed locally by introducing microwriting under a water droplet.

Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (i) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using “solvent engineering”, single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3·H2O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water molecules along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially Jsc ≈ 19 mA cm–2 and Voc ≈ 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and ∼200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current–voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations, we suggest that irreversible decomposition of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase.

Although [Ni(S2CNBu2i)(2)] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145 degrees C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120 degrees C a mixture of Ni3S4 (polydymite) and NiS results. A combined experimental and theoretical study gives mechanistic insight into the decomposition process and can be used to account for the observed differences. Upon dissolution in the primary amine, octahedral trans-[Ni(S2CNBu2i)(2)(RNH2)(2)] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90-100 degrees C leads to changes consistent with the formation of amide-exchange products, [Ni(S2CNBu(2)(i)){S2CN(H)R}] and/or [Ni{S2CN(H)R}(2)]. DFT modeling shows that exchange occurs via nucleophilic attack of the primary amine at the backbone carbon of the dithiocarbamate ligand(s). With hexylamine, amide-exchange is facile and significant amounts of [Ni{S2CN(H)Hex}(2)] are formed prior to decomposition, but with oleylamine, exchange is slower and [Ni(S2CNBu2i){S2CN(H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100 degrees C to afford nickel sulfides, even in the absence of primary amine, as shown from thermal decomposition studies of [Ni{S2CN(H)Hex}(2)]. DFT modeling of [Ni{S2CN(H)R}(2)] shows that proton migration from nitrogen to sulfur leads to formation of a dithiocarbimate (S2C-NR) which loses isothiocyanate (RNCS) to give dimeric nickel thiolate complexes [Ni{S2CN(H)R}(mu-SH)](2). These intermediates can either lose dithiocarbamate(s) or extrude further isothiocyanate to afford (probably amine-stabilized) nickel thiolate building blocks, which aggregate to give the observed nickel sulfide nanoparticles. Decomposition of the single or double amide-exchange products can be differentiated, and thus it is the different rates of amide-exchange that account primarily for the formation of the observed nanoparticulate nickel sulfides.

Highly oriented hybrid thin films composed of rod-shaped CdSe nanocrystals and poly(3-hexylthiophene) are prepared by mechanical rubbing. The orientation distribution of both CdSe nanorods and crystalline P3HT domains is determined by a combination of transmission electron microscopy (electron diffraction, low dose high-resolution TEM, and tomography), grazing incidence X-ray diffraction measurements, and UV-vis spectroscopy. After rubbing, P3HT crystalline domains show a preferential face-on orientation ((010) contact plane) and the chains align parallel to the rubbing direction. CdSe nanorods also align parallel to the rubbing direction, but the level of alignment is a function of their concentration in the polymer matrix: the lower their concentration, the higher the level of in-plane orientation of both the nanorods and the polymer chains. GIXD and electron diffraction suggest that CdSe nanorods adopt a preferential contact plane on the substrate after rubbing. The high in-plane alignment of the nanorods is mainly due to the orientation of the surrounding P3HT matrix. In particular, low dose HR-TEM shows that the local orientation of individual NRs matches the orientation of the surrounding pi-stacked P3HT chains. For a high NR concentration, bundling of NRs into larger aggregates prevents their efficient alignment by rubbing.

This work reports an extensive study about the effects of thermal treatments on the performance of TiO2-based dye-sensitized solar cells. The morphologic, structural, luminescence, and electrical properties of the as-prepared TiO2 electrode are first analyzed by using several diagnostic techniques. In particular, by extensive cathodoluminescence and photocurrent measurements it is possible to determine the energy band diagram of the material intragap levels and to observe their influence in both radiative and photoinduced transport properties. The TiO2 electrodes have been annealed at 500 degrees C for 1, 4, and 8 h in argon or in oxygen environment and then used to develop different DSSCs. The oxygen annealed solar cells show a monotonic increase in the efficiency from 6.75 up to 7.30; meanwhile, the argon-annealed solar cells have an efficiency that remains slightly constant around 6.85. By comparing the behavior of all cells parameters with the CL properties of the annealed TiO2 electrodes, it is possible to determine a correspondence between the short circuit current densities of the DSSCs and the variation of the intragap states in the semiconductor layer induced by annealing.

The various phases of tin sulfide have been studied as semiconductors since the 1960s and are now being investigated as potential earth-abundant photovoltaic and photocatalytic materials. Of particular note is the recent isolation of zincblende SnS in particles and thin-films. Herein, first-principles calculations are employed to better understand this novel geometry and its place within the tin sulfide multiphasic system. We report the enthalpies of formation for the known phases of SnS, SnS2, and Sn2S3, with good agreement between theory and experiment for the ground-state structures of each. While theoretical X-ray diffraction patterns do agree with the assignment of the zincblende phase demonstrated in the literature, the structure is not stable close to the lattice parameters observed experimentally, exhibiting an unfeasibly large pressure and a formation enthalpy much higher than any other phase. Ab initio molecular dynamics simulations reveal spontaneous degradation to an amorphous phase much lower in energy, as Sn(II) is inherently unstable in a regular tetrahedral environment. We conclude that the known rocksalt phase of SnS has been mis-assigned as zincblende in the recent literature.

The double gyroid network morphology has been the focus of extensive research efforts as one of the most appealing block copolymer structures for practical applications. We performed an extensive study of the phase behavior of the supramolecular complex PS-b-P4VP(PDP)(x) to develop a systematic route to its double gyroid morphology. The morphological characterization of complexes was accomplished by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Several compositions with the cubic Ia(3)over bard symmetry were found in a narrow region between the lamellar and the cylindrical phase. Experimental TEM images were compared to computer simulations of projections through multiple gyroid planes. Typical gyroid patterns "double wave" and "wagon wheel" were regularly found. The size of the gyroid unit cell was calculated from the SAXS data. The lattice parameter could be varied (from ca. 70 to 125 nm) by altering the molar mass of the block copolymer precursors. A number of complexes were found to exhibit characteristic biphasic morphologies coexisting lamellar and gyroid phase or gyroid and cylindrical phase. Finally, gyroid complexes with different relative PDP ratios were obtained which provides the opportunity to generate nanoporous structures with tunable porosities by dissolving the amphiphiles.

The athermal equilibrium and growth crystal shapes of a series of oligoacenes, namely, naphthalene, anthracene, and pentacene, were simulated, in a vacuum, by using three different sets of empirical potentials (UNI, UFF, and MM3 force fields). By applying the Hartman-Perdok method of the periodic bond chains (PBC), the surface profiles were obtained, providing the specific surface and attachment energy values, both for ideal and relaxed surfaces. Very good agreement among the three force fields employed was observed. From calculations, it ensues that surface relaxation only weakly affects surface and, even more, attachment energies of these semiconductor molecular crystals. It is noteworthy to point out that both equilibrium and growth shapes of these crystals are quite similar when concerning phases belonging to the same point group.

We present the formation, under ultrahigh vacuum conditions, of a three-dimensional organic architecture on a Au(111) surface based on the NH(2)-COOH interaction. The surface is first functionalized with a self-assembled monolayer (SAM) of an amine-terminated molecule (cysteamine, CA); then, a layer of benzoic acid (BA) is grown on top. We characterized this self-assembled structure by means of X-ray photoemission and absorption spectroscopy. The formation of a hydrogen bond between the two molecular species anchors the BA molecules to the CA. The structure is homogeneous in terms of its morphology and chemical properties. We also show that the structure (molecular orientation) of the BA SAM formed on the CA SAM is different from that of the BA SAM on the bare Au surface. The chemical recognition and molecular ordering nature of the BA-CA self-assembly makes it a promising candidate for the bottom-up parallel fabrication of hierarchically assembled nanodevices starting from fimctionalized building blocks.

The athermal equilibrium and growth shapes of tetracene crystal were calculated, in a vacuum, by using computer codes (CSEHP, GULP, and TINKER) along with three different sets of empirical potentials (UNI, UFF, and MM3 force fields). The surface profiles were obtained by applying the Hartman-Perdok method of the periodic bond chains (PBC). The specific surface and attachment energy values were calculated, both for ideal and relaxed surface profiles. From calculations, it follows that the equilibrium shape of tetracene shows a nearly barrel habit: one form, the (001}, rules over the other ones, and several faces roughly belong to the zone axis perpendicular to the dominant form. Concerning the growth morphology, a plate like habit with the dominant pinacoid is obtained. An excellent agreement among the three force fields employed was observed. A relevant result emerging from this work is the observation that surface relaxation in general weakly affects surface and attachment energies of molecular crystals

Great effort is being devoted to the fabrication of electronic devices based on rubrene thin films, because its outstanding charge transport properties make it one of the most promising organic semiconducting materials. Nonetheless, charge transport is strongly affected by the degree of crystallinity and degradation by photo-oxidation of rubrene. In the present work, in order to understand the dynamics of oxidation of rubrene when in the crystalline thin-film form, a combination of scanning probe techniques, such as Kelvin probe, phase contrast, and surface morphology atomic force microscopy, is used to study the oxidation process under ambient conditions of rubrene crystalline ultrathin films grown by organic molecular beam epitaxy on tetracene substrates. These films have a thickness of one or two molecular layers and consist of separated, island-like, epitaxial domains, whose orientation is determined by organic epitaxy. Theoretical calculations of the rubrene peroxide molecular dipole and structural data of rubrene and of purposely grown rubrene peroxide crystals, are exploited to determine the oxidation dynamics of such thin films and its connection with morphological, structural, and dielectric properties of the films. We demonstrate the formation of a native crystalline rubrene peroxide layer on top of the pristine rubrene crystalline domains. © 2011 American Chemical Society.

We report on the fabrication of Cu(x)O-TiO(2) (x = 1, 2) nanomaterials by an unprecedented vapor-phase approach. The adopted strategy involves the growth of porous Cu(x)O matrices by means of chemical vapor deposition (CVD), followed by the controlled dispersion of TiO(2) nanoparticles. The syntheses are performed on Si(100) substrates at temperatures of 400-550 °C under wet oxygen atmospheres, adopting Cu(hfa)(2)·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine) and Ti(O-(i)Pr)(2)(dpm)(2) (O-(i)Pr = isopropoxy; dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) as copper and titanium precursors, respectively. Subsequently, finely dispersed gold nanoparticles are introduced in the as-prepared systems via radio frequency (RF)-sputtering under mild conditions. The synthesis process results in the formation of systems with chemical composition and nano-organization strongly dependent on the nature of the initial Cu(x)O matrix and on the deposited TiO(2) amount. The decoration with low-size gold clusters paves the way to the engineering of hierarchically organized nanomaterials.

The behavior of cells in terms of cell-substrate and cell-cell interaction is dramatically affected by topographical characteristics as shape, height, and distance, encountered in their physiological environment. The combination of chemistry and topography of a biomaterial surface influences in turns, important biological responses as inflammatory events at tissue-implant interface, angiogenesis, and differentiation of cells. By disentangling the effect of material chemistry from the topographical one, the possibility of controlling the cell behavior can be provided. In this paper, surfaces with different roughness and morphology were produced by radiofrequency (RF, 13.56 MHz) glow discharges, fed with hexafluoropropylene oxide (C(3)F(6)O), in a single process. Coatings with different micro/nanopatterns and the same uppermost chemical composition were produced by combining two plasma deposition processes, with C(3)F(6)O and tetrafluoroethylene (C(2)F(4)), respectively. The behavior of osteoblast-like cells toward these substrates clearly shows a strict dependence of cell adhesion and proliferation on surface roughness and morphology.

Herein, we report the optical and magnetic properties of Mn- and Co-doped ZnO nanorods fabricated via a simple one-step aqueous-based chemical method. Interestingly, SEM results reveal a uniform size distribution of the nanorods throughout the substrate. The UV emission band of doped ZnO nanorods reveals a red shift from 382 to 384.5 nm, indicating a band-edge bending due to the dopants. The defect-related band centered at 600 urn is suppressed (I(D)/I(UV) = 1-0.35) considerably in doped nanorods, revealing the quenching of surface defects present in the nanostructures. XRD, XPS, Raman spectra, and EDS data demonstrate a successful incorporation of TM dopants in ZnO nanorods. Localized SAED patterns taken using nanoprobe size reveals that the nanorods are single crystals, grown along the c-axis [0002] direction. A systematic evalution of the enhancement in ferromagnetism (M = 0.15 x 10(-2) to 1.3 x 10(-2) emu/g) is found in modified doped ZnO nanorods.

The polymorphism of titanyl phthalocyanine films, grown on atomically flat mica substrates, has been systematically studied by micro-Raman spectroscopy, correlating structure and optical properties. Different growth regimes, using hyperthermal seeded supersonic beams, have been explored as a function of the substrate temperature. Specific signatures in micro-Raman spectra, correlated to different phases, are identified and discussed. We demonstrate the unprecedented ability to grow crystalline films at low temperature, with improved structural order, and we show that different regimes lead to grain dimensions in a range from the nanometric to the micrometric scale. The local micro-Raman analysis, carried out on crystallites with regular shapes, allows discriminating different structural phases of the single crystalline grains. We provide evidence that different growth regimes are achieved and controlled, paving the way to phase selection, which is envisaged as a key feature to improve device performance.

Thin-film blends or bilayers of donor- and acceptor-type organic semiconductors form the core of heterojunction organic photovoltaic cells. Researchers measure the quality of photovoltaic cells based on their power conversion efficiency, the ratio of the electrical power that can be generated versus the power of incident solar radiation. The efficiency of organic solar cells has increased steadily in the last decade, currently reaching up to 6%. Understanding and combating the various loss mechanisms that occur in processes from optical excitation to charge collection should lead to efficiencies on the order of 10% in the near future. In organic heterojunction solar cells, the generation of photocurrent is a cascade of four steps: generation of excitons (electrically neutral bound electron-hole pairs) by photon absorption, diffusion of excitons to the heterojunction, dissociation of the excitons into free charge carriers, and transport of these carriers to the contacts. In this Account, we review our recent contributions to the understanding of the mechanisms that govern these steps. Starting from archetype donor-acceptor systems of planar small-molecule heterojunctions and solution-processed bulk heterojunctions, we outline our search for alternative materials and device architectures. We show that non-planar phthalocynanines have appealing absorption characteristics but also have reduced charge carrier transport. As a result, the donor layer needs to be ultrathin, and all layers of the device have to be tuned to account for optical interference effects. Using these optimization techniques, we illustrate cells with 3.1% efficiency for the non-planar chloroboron subphthalocyanine donor. Molecules offering a better compromise between absorption and carrier mobility should allow for further improvements. We also propose a method for increasing the exciton diffusion length by converting singlet excitons into long-lived triplets. By doping a polymer with a phosphorescent molecule, we demonstrate an increase in the exciton diffusion length of a polymer from 4 to 9 nm. If researchers can identify suitable phosphorescent dopants, this method could be employed with other materials. The carrier transport from the junction to the contacts is markedly different for a bulk heterojunction cell than for planar junction cells. Unlike for bulk heterojunction cells, the open-circuit voltage of planar-junction cells is independent of the contact work functions, as a consequence of the balance of drift and diffusion currents in these systems. This understanding helps to guide the development of new materials (particularly donor materials) that can further boost the efficiency of single-junction cells to 10%. With multijunction architectures, we expect that efficiencies of 12-16% could be attained, at which point organic photovoltaic cells could become an important renewable energy source.

The effect of block copolymer chain connectivity on the structure formation in binary blends comprising block copolymer hosts and enthalpically neutralized particle filters is investigated for linear diblock (AB) and triblock (ABA and BAB) as well as four-arm star copolymer architectures (AB(3) and A(3)B). For particles with approximately constant effective size (defined here as the ratio of filler particle diameter to host polymer radius of gyration), miscibility was observed only within diblock copolymers and within the domains formed by the end blocks of triblock copolymers. The limitation of particle miscibility within the triblock mid-domain is interpreted as a consequence of the entropy loss associated with particle deposition due to the stretched configuration of bridged midblock chains. Particle aggregation was observed in both star copolymer samples irrespective of the architecture of the particle-loaded polymer domain. In the case of particle loading of the branched copolymer domain, this is rationalized as a consequence of the increased effective particle size, whereas the incompatibility of particle fillers in the linear block. domain of miktoarm copolymer hosts is interpreted as a result of the coupling of dimensional changes within the microstructure along with the reduced axial compressibility of the particle-free branched domain. The sensitive dependence of the particle compatibility oil the chain architecture of the polymer host illustrates a yet unexplored parameter space that will need to be taken into account if particle blends are to be designed with branched or multiblock host copolymer architectures. Macromolecules

Polymer-fullerene bilayer heterostructures are suited to study excitonic processes in conjugated polymers. Excitons are efficiently quenched at the polymer-fullerene interface, whereas the polymer-vacuum interface is often considered as an exciton-reflecting interface. Here, we report about efficient exciton quenching close to the polymer-vacuum interface of spin-coated MDMO-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene]) films. The quenching efficiency is estimated to be as high as that of the polymer-fullerene interface. This efficient quenching is consistent with enhanced intermolecular interactions close to the polymer-vacuum interface due to the formation of a "skin layer" during the spin-coating procedure. In the skin layer, the polymer density is higher; that is, the intermolecular distances are shorter than in the rest of the film. The effect of exciton quenching at the polymer-vacuum interface should be taken into account when the thickness of the polymer film is on the order of the exciton diffusion length; in particular, in the determination of the exciton diffusion length. © 2009 American Chemical Society.

The relation between the morphology, optical, and photoconductive properties of thin-film bulk heterojunctions of poly(3-hexylthiophene) (P3HT) with a series of electron-accepting siloxanes with a different number (x = 2, 4, 5) of pendant naphthalene diimide (NDIS) moieties is reported. All NDIS siloxanes show good electronaccepting properties, when blended with P3HT. Interestingly, the film (nano)morphology can be controlled by relatively small changes in the molecular structure of the NDIS siloxanes. Spin-coating from orthodichlorobenzene (ODCB) yields complex film (nano)morphologies, being correlated with the weight ratios of P3HT and NDIS siloxanes, and the molecular structure of the latter. On the other hand, all blends spincoated from chloroform (CHCl3) show good mixing of the components at the molecular level. It is inferred that the nanomorphology of the blends can greatly influence their photoconductive properties: samples spincoated from ODCB invariably display a higher photoconductance than corresponding samples spin-coated from CHCl3. This is explained in terms of a higher mobility of holes in samples spin-coated from ODCB, as measured by time-resolved microwave conductivity measurements. These data are useful to delineate the conditions for the research in strives for efficient organic photovoltaics. © 2009 American Chemical Society.

Water-soluble sulfonated monomer based on 3,4-propylenedioxythiophene (ProDOT-sultone) was synthesized and characterized for the first time via the O-alkylation of the corresponding unreactive beta,beta-disubstituted hydroxyl group with propane sultone in the presence of a catalytic amount of 1,4-diazabicyclo[2.2.2]octane (DABCO). This new monomer was oxidatively polymerized to produce regioregular water-soluble conjugated anionic polyelectrolyte, which was then used for the fabrication of solid-state electrochromic devices using the layer-by-layer (LbL) deposition method. These solid-state devices were found to exhibit better electrochromic properties in terms of color contrast, switching time, coloration efficiency (CE), surface control electroactivity, and conductivity in thin films compared with the corresponding water-soluble regiorandom 3,4-ethylenedioxythiophene (EDOT) derivative. For the 40 and 80 bilayer solid-state electrochromic devices, the electrochemical contrast was observed to be 31 and 40% at 570 nm with fast solid-state switching times of 100 and 220 ins, respectively, indicating faster movement of the ions in and out of the films. Furthermore, the CE was found to be as high as 250 cm(2)/C for the 80 bilayer device and was independent of the device thickness, indicating the full accessibility of all of the ionic sites, even in thicker films. Four-point probe conductivity of the LbL and in situ conductivity of solution cast films were found to be in the range of 10(-4) and 10(-3) S/cm, respectively.

Nitrogen-doped TiO2 materials were successfully prepared following three different preparation routes (sol−gel, mechanochemistry, and oxidation of TiN) and characterized by X-ray diffraction, electron microscopy, and various spectroscopic techniques. All samples absorb visible light, and the one obtained via sol−gel, showing the anatase structure, is the most active in the decomposition of organic compounds under visible light. Various nitrogen-containing species have been observed in the materials, whose presence and abundances depends on the preparative route. Ammonium NH4+ ions are residual of the synthesis using ammonium salts (sol−gel, mechanochemistry) and are quite easily eliminated, as shown by the parallel behavior of both NMR and XPS spectra. Cyanide CN− ions form at high temperature in parallel with the phase transition of the solid to rutile. Molecular nitric oxide forms in the case of materials exhibiting close porosity. The already reported bulk radical species, Nb•, is the only paramagnetic...

The well-established ability of copolymer micelles to encapsulate and release hydrophobic molecules has been investigated following their adsorption onto silica particles. Here, a pH-responsive copolymer, poly(2-(dimethylamino)ethyl methacrylate)- b-poly(2-(diethylamino)ethyl methacrylate) (PDMA(106)- b-PDEA(25)), has been used to study the formation and dissociation of adsorbed micelles through pH variation. This copolymer behaves as free unimers in aqueous solutions below pH 8 and forms micelles 29 nm in hydrodynamic diameter above this pH. Encapsulation and release of a model hydrophobic compound (pyrene) by in situ adjustment of the solution pH has been compared for both free and adsorbed micelles using fluorescence spectrophotometry, epifluorescence microscopy, and zeta potential measurements. At basic pH values, pyrene is solubilized within the cores of micelles adsorbed on silica particles: addition of acid leads to micelle dissociation and release of the pyrene into the bulk aqueous solution. Micelle adsorption does not appear to hinder the extent of pyrene uptake/release. Moreover, this pH-responsive behavior is both reversible and reproducible over multiple pH cycles.

A series of chiral, substituted conjugated polymers containing the cyclopenta[2,1-b:3,47b']dithiophene unit were synthesized: poly(cyclopenta[2, 1-b:3,4-b']dithiophene)s, poly(thieno[3,2-b]thiophene-alt-cyclopenta[2,1-b:3,4-b']dithiophene)s and poly(thiophene-alt-cyclopenta[2,1-b:3,4-b']dithiophene)s. The polymers were prepared by a Stille-coupling reaction and their (chir)optical properties were investigated in solution as well as in film. UV-vis and fluorescence spectroscopy indicated that the polymers are present as rigid, highly conjugated strands in solution. Although the homopolymers (poly(cyclopenta[2, 1-b:3,4-b']dithiophene)s) do not self-assemble in solution as well as in film, the alternating copolymers (chirally) stack upon transition to nonsolvents and solid state. The (chir)optical properties in film appeared to depend on the annealing conditions: initially, the chiroptical response increases, but at higher temperatures, the Cotton effects irreversibly disappear. Moreover, the CD spectra of films of poly(thieno[3,2-b]thiophene-alt-cyclopenta[2,1-b:3,4-b']dithiophene)s with chiral substituents on the thieno[3,2-b]thiophene moiety appeared to be a superposition of two effects, which had a different annealing dependency. In poly(thiophene-alt-cyclopenta[2, 1-b:3,4-b']dithiophene)s, only chiral exciton coupling was found to be present. ispartof: Macromolecules vol:41 issue:3 pages:591-598 status: published

A series of chiral 3,6-substituted poly(thieno[3,2-b]thiophene)s (PTTs) were synthesized: 3,6-dialkoxy-substituted PTTs, 3,6-dialkylthio-substituted PTTs, and alternating copolymers of 3,6-dialkoxythieno-[3,2-b]thiophenes and 3,6-dialkylthieno[3,2-b]thiophenes. The polymers were prepared by a Stille-coupling reaction and their (chir)optical properties were investigated in solution as well as in film. The substituent appeared to play a decisive role in the polymer's macromolecular structure and supramolecular organization. The very small steric hindrance between the substituents and the polymer backbone of dialkoxy-substituted PTTs, in addition to the strong chalcogen-chalcogen attractions, allows these polymers to adopt a rigid rod-like conformation in good solvents. Upon transition to nonsolvents and film, the polymer strands chirally stack but no macroscopic order could be obtained. If the steric hindrance between adjacent monomer units is increased and the strength of the chalcogen-chalcogen attraction is decreased, as is the case in dialkylthio-substituted PTTs and the alternating copolymers, the polymers are present as random coils in solution. In films or in poor solvents, they planarize and stack and macroscopic order is present. Very large Cotton effects in both poor solvents and film were observed. In film, the CD spectra of some of the (semi-crystalline) polymers is a combination of "real" CD and other contributions. ispartof: Macromolecules vol:41 issue:3 pages:568-578 status: published