The compositions and structures of the conjugated polymer poly(2,5-bis(3-hexadecylthiophen-2-yl)thienothiophene) (PBTTT-C-16) are quantitatively measured and distinguished for the crystalline and disordered regions, as well as the intermolecular interactions between phenyl-C-71-butyric acid methyl ester (PC71BM) and PBTTT moieties in bulk heterojunctions (BHJs). For PBTTT-C-16, the long-range (>10 nm) crystalline order of lamellae is established by two-dimensional (2D) grazing-incidence small-angle X-ray scattering (GISAXS), while short-range (<1 nm) structures are characterized by using solid-state nuclear magnetic resonance (NMR) spectroscopy. In particular, 2D H-1{H-1} double-quantum and C-13{H-1} heteronuclear correlation NMR spectra reveal distinct intensity correlations for PBTTT-C-16 that provide direct evidence for the presence of regions with well-ordered pi-pi-stacked conjugated backbones and interdigitated alkyl side chains, stacked backbones and disordered side chains, and amorphous regions of PBTTT-C-16. Good agreement is found between the X-ray diffraction (XRD) and solid-state NMR analyses for H-1-H-1 distances between interlayer aromatic moieties (3.7 & Aring; from XRD, 3.6 & Aring; from 2D H-1{H-1} NMR) and for the intermolecular C-H distances between the aromatic hydrogen atoms and terminal methyl carbon atoms (3.3-3.4 & Aring; from XRD, 3.3 & Aring; from 2D C-13{H-1} NMR) in the crystalline regions. A larger mean H-1-H-1 distance of >3.8 & Aring; between interlayer PBTTT backbones in less-ordered and disordered regions is determined by NMR, which is otherwise difficult to assess by XRD analyses alone. Combined solid-state NMR and density functional theory (DFT) results corroborate that the conjugated PBTTT-C-16 backbones adopt nearly coplanar conformations in the ordered regions with a distribution of dihedral angles bisecting the thienothiophene moieties in the amorphous regions. The polar five-membered ring of the C-70 fullerene in the PBTTT-C-16:PC71BM blend was found to interact strongly with the aromatic thienothiophene protons of the semiconducting polymer, causing a strong pi-pi overlap of distinct moieties of the fullerene and polymer chain. The relative displacements of H-1 chemical shifts by local ring currents and measurements of homonuclear H-1 dipole-dipole couplings allow the molecular proximities between specific chemical moieties of the electron-donating PBTTT and the electron-accepting PC71BM species in the bimolecular BHJs to be established.

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both internal and external (i.e., related to interactions with the dielectric layer), especially for n-type materials. Internal dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (<a-few-hundred cm(-1)), which makes it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be external, being controlled by the gate insulator dielectric properties. Here a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory, and simulations is reported. Unambiguous evidence that ad hoc molecular design enables the electron charge carriers to be freed from both internal and external disorder to ultimately reach band-like electron transport is provided.

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both intrinsic and extrinsic, especially for n-type materials. Intrinsic dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be extrinsic, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both intrinsic and extrinsic disorder to ultimately reach band-like electron transport.

Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials.

Poly(3-alkylthiophenes) are one of the most frequently used conjugated polymer classes in organic photovoltaics. Here, a generalized packing model for the polythiophene main chains in the crystalline form I of high molecular weight regioregular poly(3-alkylthiophenes) with extended side chains (pentyl through octyl) is reported. The model is based on structural constraints from solid-state NMR: short internuclear distances of less than 4.0 angstrom of neighboring thiophene protons parallel to the stacking direction and the isotropic chemical shift for the thiophene protons is high-field shifted by 0.9 +/- 0.1 ppm. Nucleus-independent chemical shift calculations show that only the most recent structure for P3HT (space group P2(1)/c) is compatible with these structural constraints. On this basis, a generalized packing model is developed, showing that slipping parallel to the stacked polymer chains of up to 1.5 angstrom is allowed, while out-of-plane tilts perpendicular to the stacked chains are only tolerated up to 20 degrees.

The AIRSS method generates crystal structures for m-aminobenzoic acid; comparison is made to experimental powder X-ray diffraction and MAS NMR.

DPP-DTT adopts a donor-on-acceptor stacking arrangement which is preserved in thin films.

Institut des Sciences Analytiques, Centre de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Department of Chemistry, Lancaster Uni j.griffin@lancaster.ac.uk Department of Chemistry, University of Ca 1EW, UK Optoelectronics Group, Cavendish Laborato Avenue, Cambridge CB3 0HE, UK Laboratory for Chemistry of Novel Materia Materials and Polymers (CIRMAP), Univers 7000 Mons, Belgium Institut des Sciences et Ingénierie Chim Lausanne (EPFL), CH-1015 Lausanne, Switz † Electronic supplementary informa computational and experimental de preparation. See DOI: 10.1039/c7sc00053g Cite this: Chem. Sci., 2017, 8, 3126

Could molecular semiconductors one day compete with their inorganic counterparts? On page 7106, S. Seki, Y. H. Geerts and co-workers unravel, by field-induced time-resolved microwave conductivity measurements, an unprecedentedly high average interfacial mobility of 170 cm2 V−1 s−1 for 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene over short length- and time-scales. Approaching for the first time the hole mobility in single-crystalline silicon, these results hold great promise for the field of organic electronics.

The structural and electronic properties of four isomers of didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT) have been investigated. Results show the strong impact of the molecular packing on charge carrier transport and electronic polarization properties. Field-induced time-resolved microwave conductivity measurements unravel an unprecedented high average interfacial mobility of 170 cm(2) V-1 s(-1) for the 2,7-isomer, holding great promise for the field of organic electronics.

The synthesis and structural characterization of various aromatic–aliphatic polyamides are reported in this study. The polymers are obtained by solution polymerization of p-phenylenediamine with various aliphatic diacid chlorides. The resulting polyamides are labeled PA P-X, where X varies between 5 and 10 and corresponds to the number of carbon atoms of the dicarboxylic acid monomers used in the synthesis. The polyamides are obtained with Mn values of 10 kg/mol or higher, as determined by solution NMR spectroscopy and gel permeation chromatography (GPC). The polymers PA P-5 to PA P-8 degrade prior to melting, whereas only PA P-10 shows melting on heating. The structural changes in the polymers, with increasing methylene segments, are investigated by X-ray diffraction and molecular modeling. Conformational changes as a function of temperature have been studied by solid-state NMR spectroscopy. These studies have been illustrative in following the phase transformations in the aromatic–aliphatic polymers. Fo...

Pervasive in Nature, the propane unit is an essential component of numerous bioactive molecules. These range from acyclic systems, such as the neurotransmitter γ-aminobutyric acid, through to the bicyclic nuclei of various chromanes and dihydrobenzofurans. In the latter case, cyclisation via cyclic ether formation ensures a highly pre-organised structure, whilst linear scaffolds display more dynamic conformational behaviour resulting from rotation about the two internal C(sp3 )-C(sp3 ) bonds. In this study, the replacement of -[CH2 ]- units by -[CHF]- centres is evaluated as a strategy to achieve acyclic conformational control by hindering these internal rotations. Reinforcing, non-covalent fluorine interactions are validated as powerful design features that result in programmable conformational behaviours: These are encoded by the relative configuration of each centre. By exploiting cooperative neighbouring stereoelectronic effects in a multi-vicinal fluoroalkane it is possible to emulate the overall conformation of the dihydrobenzofuran scaffold found in a variety of natural products with an acyclic mimic. This is described as a function of two bond vectors at the chain termini and validated by combined theoretical, crystallographic and spectroscopic analyses. In view of the favourable physicochemical properties associated with fluorine introduction, this approach to bioactive scaffold design may prove to be expansive.

The polymerization of alkoxy-substituted [2.2]paracyclophane-1,9-dienes via ring-opening metathesis polymerization (ROMP) to obtain soluble poly(p-phenylenevinylene)s is a versatile method due to its living nature which enables the possibility of block copolymerization and end group modification. However, detailed studies on the reactivity behavior and the polymerization process of alkoxy-substituted [2.2]paracyclophane-1,9-dienes have not been reported so far. Herein we present a detailed study on the varying tendencies of the four isomers of dimethoxy-(2-ethylhexyloxy)-[2.2]paracyclophane-1,9-diene to undergo ROMP. Therefore, we carried out polymerization combining all individual isomers with five different metathesis catalysts and collected initiation and propagation kinetics for various combinations. Furthermore, we revealed a specific coordination of the monomer repeating unit to the catalyst during the polymerization process and succeeded to polymerize not only the pseudogeminal isomers but also one of the pseudo-ortho isomers.

As part of our ongoing study investigating isohexide-based polyamides, we have synthesized isosorbide(bis(propan-1-amine)) (DAPIS) and studied its reactivity in the polymerization towards fully biobased polyamides.

Modern ab initio calculations predict ionic and superionic states in highly compressed water and ammonia. The prediction apparently contradicts state-of-the-art experimentally established phase diagrams overwhelmingly dominated by molecular phases. Here we present experimental evidence that the threshold pressure of ~120 GPa induces in molecular ammonia the process of autoionization to yet experimentally unknown ionic compound—ammonium amide. Our supplementary theoretical simulations provide valuable insight into the mechanism of autoionization showing no hydrogen bond symmetrization along the transformation path, a remarkably small energy barrier between competing phases and the impact of structural rearrangement contribution on the overall conversion rate. This discovery is bridging theory and experiment thus opening new possibilities for studying molecular interactions in hydrogen-bonded systems. Experimental knowledge on this novel ionic phase of ammonia also provides strong motivation for reconsideration of the theory of molecular ice layers formation and dynamics in giant gas planets. Ionization of highly compressed ammonia has previously been predicted by computation. Here, the authors provide experimental evidence for this autoionization process at high pressures, showing the transformation of molecular ammonia into ammonium amide.

A new approach towards polyolefin-like copolyesters is introduced based on a single set of reaction conditions. The delicate balance between steric hindrance and monomer reactivity determines whether random or block copolymers are formed.

Discotic hydrazone molecules are of particular interest as they form discotic phases where the discs are rigidified by intramolecular hydrogen bonds. Here, we investigate the thermotropic behavior and solid-state organizations of three discotic hydrazone derivatives with dendritic groups attached to their outer peripheries, containing six, eight, and ten carbons of linear alkoxy chains. On the basis of two-dimensional wide angle X-ray scattering (2DWAXS), the elevated temperature liquid crystalline (LC) phases were assigned to a hexagonal columnar (Colh) organization with nontilted hydrazone discs for all three compounds. With WAXS, advanced solid-state nuclear magnetic resonance (SSNMR) techniques, and ab initio computations, the compounds with six and ten carbons of achiral alkoxy side chains were further subjected to studies at 25 °C, revealing complex crystalline phases with rigid columns and flexible side chains. This combined approach led to models of coexisting helical columnar stacking morphologies for both systems with two different tilt/pitch angles between successive hydrazone molecules. The differences in tilt/pitch angles between the two compounds illustrate that the columns with short alkoxy chains (six carbons) are more influenced by the presence of other stacks in their vicinity, while those with long side chains are less tilted due to a larger alkoxy (ten carbons) buffer zone. The formation of different packing morphologies in the crystalline phase of a columnar LC has rarely been reported so far, which suggests the possibility of complex stacking structures of similar organic LC systems, utilizing small molecules as potential materials for applications in organic electronics.