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Conjugated rod-coil diblock copolymers self-assemble due to a balance of liquid crystalline (rod-rod) and enthalpic (rod-coil) interactions. Previous work has shown that while classical block copolymers self-assemble into a wide variety of nanostructures, when rod-rod interactions dominate self-assembly in rod-coil block copolymers, lamellar structures are preferred. Here, it is demonstrated that other, potentially more useful, nanostructures can be formed when these two interactions are more closely balanced. In particular, hexagonally packed polylactide (PLA) cylinders embedded in a semiconducting poly(3-alkylthiophene) (P3AT) matrix can be formed. This microstructure has been long-sought as it provides an opportunity to incorporate additional functionalities into a majority phase nanostructured conjugated polymer, for example in organic photovoltaic applications. Previous efforts to generate this phase in polythiophene-based block copolymers have failed due to the high driving force for P3AT crystallization. Here, we demonstrate that careful design of the P3AT moiety allows for a balance between crystallization and microphase separation due to chemical dissimilarity between copolymer blocks. In addition to hexagonally packed cylinders, P3AT-PLA block copolymers form nanostructures with long-range order at all block copolymer compositions. Importantly, the conjugated moiety of the P3AT-PLA block copolymers retains the crystalline packing structure and characteristic high time-of-flight charge transport of the homopolymer polythiophene (μh∼ 10-4 cm2 V-1 s-1) in the confined geometry of the block copolymer domains. [ABSTRACT FROM AUTHOR]

Inelastic light scattering spectroscopy has, since its first discovery, been an indispensable tool in physical science for probing elementary excitations, such as phonons, magnons and plasmons in both bulk and nanoscale materials. In the quantum mechanical picture of inelastic light scattering, incident photons first excite a set of intermediate electronic states, which then generate crystal elementary excitations and radiate energy-shifted photons. The intermediate electronic excitations therefore have a crucial role as quantum pathways in inelastic light scattering, and this is exemplified by resonant Raman scattering and Raman interference. The ability to control these excitation pathways can open up new opportunities to probe, manipulate and utilize inelastic light scattering. Here we achieve excitation pathway control in graphene with electrostatic doping. Our study reveals quantum interference between different Raman pathways in graphene: when some of the pathways are blocked, the one-phonon Raman intensity does not diminish, as commonly expected, but increases dramatically. This discovery sheds new light on the understanding of resonance Raman scattering in graphene. In addition, we demonstrate hot-electron luminescence in graphene as the Fermi energy approaches half the laser excitation energy. This hot luminescence, which is another form of inelastic light scattering, results from excited-state relaxation channels that become available only in heavily doped graphene. [ABSTRACT FROM AUTHOR]

The aqueous self-assembly of a sequence-specific bioinspired peptoid diblock copolymer into monodisperse superhelices is demonstrated to be the result of a hierarchical process, strongly dependent on the charging level of the molecule. The partially charged amphiphilic diblock copolypeptoid 30-mer, [N-(2-phenethyl)glycine]15-[N-(2-carboxyethyl)glycine]15, forms superhelices in high yields, with diameters of 624 ± 69 nm and lengths ranging from 2 to 20 μm. Chemical analogs coupled with X-ray scattering and crystallography of a model compound have been used to develop a hierarchical model of self-assembly. Lamellar stacks roll up to form a supramolecular double helical structure with the internal ordering of the stacks being mediated by crystalline aromatic side chain-side chain interactions within the hydrophobic block. The role of electrostatic and hydrogen bonding interactions in the hydrophilic block is also investigated and found to be important in the self-assembly process. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid devices built from organic and inorganic moieties are being actively researched as replacements for inorganic electronics, thermoelectrics, and photovoltaics. However, energy transport and conversion, at the organic–inorganic interface is not well understood. One approach to study this interface is to look at the smallest hybrid building block – the heterojunction of a single organic molecule with inorganic contacts. We present a review of this work, focused on fundamental transport properties of metal–molecule–metal junctions that are related to thermoelectric energy conversion, i.e., electronic conductance, thermopower, and thermal conductance. We describe the motives, strategies, and future directions for considering heterojunctions as building blocks for thermoelectric materials. [Copyright &y& Elsevier]

The heterogeneous microstructure of semicrystalline polymers complicates the relationship between their electrical conductivity and carrier concentration. Charge transport models typically describe conductivity with an assumption of uniform doping throughout the material. Here, the evolution in morphology and optoelectronic properties of poly(3‐hexylthiophene) (P3HT) is reported as a function of carrier concentration in an organic electrochemical transistor using a polymeric ionic liquid (PIL) as the gate insulator. Operando grazing incidence X‐ray scattering reveals that negatively charged ions from the dielectric first infiltrate the amorphous regions of the semiconductor, and then penetrate the crystalline regions at a critical carrier density of 4 × 1020 cm−3. Upon infiltration, the crystallites expand by 12% in the alkyl stacking direction and compress by 4% in the π–π stacking direction. The change in crystal structure of P3HT correlates with a sharply increasing effective carrier mobility. UV–visible spectroscopy reveals that holes induced in P3HT first reside in the crystalline regions of the polymer, which verifies that a charge carrier need not be in the same physical domain as its associated counterion. The dopant‐induced morphological changes of P3HT rationalize the dependence of mobility on carrier concentration, suggesting a phase transition of crystalline regions at high carrier concentration. Operando grazing incidence X‐ray scattering reveals structural changes during electrochemical gating of poly(3‐hexylthiophene) transistors using a polymeric ionic liquid gate dielectric. [ABSTRACT FROM AUTHOR]

Charge transport in semiconducting polymers is inextricably linked to their microstructure, making the characterization of polymer morphology at all length‐scales essential for understanding the factors that limit mobility in these materials. Indeed, charge transport depends both on the ability of polarons to delocalize at the approximately nanometer length‐scale and navigate a complex energetic and morphological mesoscale landscape. While characterization of the mesoscale morphology of polymers is well‐established, studies of the local chain packing and nanoscale disorder, which affect delocalization, can be significantly more difficult to carry out. Through infrared charge modulation spectroscopy and theoretical modeling, the effect of the local chain environment on polaron delocalization is directly measured and quantified. Using a series of polymers based on the model system, poly(3‐hexylthiophene), the link between disorder and polaron localization is systematically explored. Polaron delocalization is correlated with known trends in mobility, revealing that while charge delocalization is always beneficial, the formation of tie‐chains is necessary to reach the highest mobilities in semicrystalline polymers. The results provide direct evidence for the importance of both nanoscale (charge carrier delocalization) and mesoscale (tie‐chains) orders, demonstrating the need to distinguish the key length‐scale limiting charge transport in the design of new, high mobility polymers. Quantitative infrared studies of polaron absorption combined with a vigorous and complete theoretical model reveal rich information about the local, nanoscale packing of a series of polymers based on poly(3‐hexylthiophene). Correlating these insights to independent studies of carrier mobility, direct evidence for the effect of charge localization and crystallite connectivity on charge transport is shown. [ABSTRACT FROM AUTHOR]