Preferred Formation of Minority Concomitant Polymorphs in 2D Self‐Assembly under Lateral Nanoconfinement

Control over polymorph formation in the crystallization of organic molecules remains a huge scientific challenge. Now, preferential formation is presented of one polymorph, formed by chiral molecules, in controlled two‐dimensional (2D) nanoconfinement conditions at a liquid–solid interface. So‐called nanocorrals to control concomitant polymorph formation were created in situ via a nanoshaving protocol at the interface between 1‐phenyloctane and covalently modified highly‐oriented pyrolytic graphite (HOPG). The preferentially formed polymorphs, which were less stable in the large‐scale monolayers, could be selected simply by varying the orientation of the square nanocorrals with respect to the HOPG lattice

Enhancing singlet oxygen generation by self-assembly of a porphyrin entrapped in supramolecular fibres

Singlet oxygen (SO) is one of the reactive oxygen species that is effective in various uses, including performing chemical reactions, treating water impurities, and aiding in medicinal therapy. The generation of SO is often efficient in solution, although generation from the solid phase in nanomaterials is less reliable. Here, we report the preparation of hybrid supramolecular materials that incorporate a photosensitizer within their nanostructured fibers and demonstrate their high efficiency in promoting SO formation. The incorporation of tetrakis(4-carboxyphenyl)porphyrin within the nanofibers of a bis-imidazolium gelator was proved by various techniques, including super-resolution radial fluctuations (SRRF) microscopy, which shows the location of the chromophore precisely. SO is generated from the dispersed nanofibers far more efficiently than the dissolved porphyrin; a 14-fold higher rate is observed initially. These results point to an effective approach to the generation of SO for several applications, from optimizing synthetic protocols to photomedicine

Functional supramolecular tetrathiafulvalene-based films with mixed valences states

Tetrathiafulvalene molecules substituted with a carboxylic acid group (TTFCOOH) were bound as redox-active moieties into a poly(4-vinyl pyridine) (P4VP) skeleton through non-covalent interactions (hydrogen bonds). The aspect of the resulting P4VP-TTFCOOH films showed a uniform and smooth morphology. Moreover, the redox function of TTFCOOH in P4VP-TTFCOOH was demonstrated using tetrachloroauric acid, iron(III) perchlorate and iodine vapors as doping agents. The oxidized states of TTFCOOH as well as the mixed valance state TTFCOOH0-TTFCOOH+• were generated in a controlled manner in solid state, resulting in an organic film capable of charge transport. The charge transport along the organic donor molecules hydrogen bonded to the polymer matrix was demonstrated employing Electrostatic Force Microscopy (EFM)Postprint (author's final draft

Crystal structure analyses facilitate understanding of synthesis protocols in the preparation of 6,6′-dibromo-substituted BINOL compounds

A combination of crystallographic and spectroscopic techniques has been used in order to address thorough purification protocols for a series of atropisomeric 1,1′-binaphthalene-2,2′-diol (BINOL) derivatives to be used as building blocks for chiral nanoscale constructs

Enhancing Singlet Oxygen Generation by Self-Assembly of a Porphyrin Entrapped in Supramolecular Fibers

Singlet oxygen (SO) is one of the reactive oxygen species that is effective in various uses, including performing chemical reactions, treating water impurities, and aiding in medicinal therapy. The generation of SO is often efficient in solution, although generation from the solid phase in nanomaterials is less reliable. Here, we report the preparation of hybrid supramolecular materials that incorporate a photosensitizer within their nanostructured fibers and demonstrate their high efficiency in promoting SO formation. The incorporation of tetrakis(4-carboxyphenyl)porphyrin within the nanofibers of a bis-imidazolium gelator was proved by various techniques, including super-resolution radial fluctuations (SRRF) microscopy, which shows the location of the chromophore precisely. SO is generated from the dispersed nanofibers far more efficiently than the dissolved porphyrin; a 14-fold higher rate is observed initially. These results point to an effective approach to the generation of SO for several applications, from optimizing synthetic protocols to photomedicine

Stereochemistry and Twisted Crystals

This review article discusses a link between stereochemistry and structural and morphological chirality. We present the remarkably frequent, but less often reported, growth of twisted crystals and discuss the reasons for their formation and ways to favor their growth. The more commonly encountered conglomerates and racemic compounds can be formed by achiral molecules, but the emergence of morphological chirality is often not considered in this context and perhaps deserves attention. Twisted crystals are known for a wide variety of materials, molecular and macromolecular, complexes and oxides, and so on. In growing crystals, twisting of lamellae because of strain generated during growth eventually unwinds in larger objects, and may not be detected. This kind of chiral morphology arising from low symmetry growth, and the challenges and opportunities for research in the area, are highlighted. In particular, the link between structural bending in supramolecular aggregates in solution or at interfaces, chiral nanofilaments in liquid crystals, and chiral polymers, is discussed

Supramolecular block copolymers incorporating chiral and achiral chromophores for the bottom-up assembly of nanomaterials

The coordination of the chiral metalloporphyrin ([5,10,15,20-[4-(R,R,R,R)-2-N-octadecylamidoethyloxiphenyl]porphyrin] zinc (II)) and an achiral homologue to an amphiphilic block copolymer of poly(styrene-b-4-vinyl pyridine) (PS-b-P4VP) have been studied in solution and as cast material. The resulting chiral dye-polymer hybrid material has been accomplished via axial coordination between the zinc (II) metal ion in the core of the porphyrin ring and the pyridyl units of the block-copolymer in a non-coordinative solvent. The supramolecular organization and possible chirality transfer to the hybrid material have been studied in solution by UV-visible absorption spectroscopy, fluorescence spectroscopy, Nuclear Magnetic Resonance and Circular Dichroism. The morphology of the chiral and achiral doped polymers has been studied in solid state by Transmission Electron Microscopy and Atomic Force Microscopy. We show that the nanostructures formed depend greatly upon the nature of the side-chains on the porphyrins, where a chiral group leads to a very homogeneous phase-separated material, perhaps indicating that chiral side groups are useful for the preparation of this type of supramolecular hybridPostprint (author's final draft

Quantification of energy of activation to supramolecular nanofibre formation reveals enthalpic and entropic effects and morphological consequence

We show a self-assembly process leading to fibres from a system that starts far from equilibrium because of fast solvent – anti-solvent mixing and analyse the activation energies associated with the aggregation. It is in some ways reminiscent of diverse natural fibrous materials that have kinetic behaviour dominated by a rate limiting induction period followed by rapid growth. A full thermodynamic rationale for these systems and related synthetic ones is required for a full understanding of the driving force of their non-equilibrium self-assembly. Here we determine quantitatively the enthalpy and entropy of activation for the processes leading to the growth of fibres of this type, that contrasts with analysis of other systems where final energetic states are analysed. A dramatic effect is revealed whereby comparatively small changes in temperature or solvent composition (the ratio of water to ethanol) lead to alterations in the relative importance of enthalpy and entropy of activation and massive changes in the speed of fibre formation. The characteristics of the kinetic model adopted show a correlation with the fibre morphology of the self-assembled materials, which are isostructural according to diffraction experiments: The control of growth can lead to fibres only two bilayers thick. The crossover in behaviour is characteristic of the solvent mixture and the thermodynamic analysis points to the origins of this effect where different assembly routes are viable under only marginally different conditions

Solid state supramolecular structure of diketopyrrolopyrrole chromophores: correlating stacking geometry with visible light absorption

Mono- and di-alkylated 1,4-diketo-3,6-dithiophenylpyrrolo[3-4-c]pyrrole derivatives (TDPPs) have been synthesised and their solid state packing and absorption properties have been correlated. In this library of compounds the bulkier substituents distort the geometry of the chromophores and shift the lowest energy absorption band as a consequence of reduced π–π stacking and inter-chromophore overlap. Longitudinal displacement of the conjugated core is affected by donor–acceptor intermolecular interactions and twisting of the thiophene ring out of the plane of the DPP core, whereas lateral displacement was correlated to distortion of the NLactam–C(R) bond out of the plane of the DPP core. The di-substituted TDPP with hexyl units exhibit high molecular planarity, strong close packing of the conjugated core and significant red shift of the maximum of absorption in the solid, whereas the mono-substituted compounds with hexyl and ethyl acetate units are the least distorted of the series because of strong intermolecular hydrogen bonding that increases the molecular overlap and planarity of the chromophores. Therefore the family of mono-substituted TDPPs and more specifically the ones with ethyl acetate substituents show good potential for modulating the molecular geometry and optimizing the charge transport in materials for organic electronic applications

Towards more sustainable synthesis of diketopyrrolopyrroles

The alkylation of 1,4-diketo-3,6-arylpyrrolo[3,4-c]pyrroles (ArDPP) is one of the most important steps in the synthesis of soluble materials based on these molecules and the polymers derived from them (that are employed widely in putative organic solar cells). Here we report an improvement in their method of synthesis replacing habitual solvent and base. Compared with more usual conditions, we employed acetonitrile as solvent to give higher or similar yields, with less toxic and hazardous waste, lower reaction time and temperature, and allows recycling of unreacted starting materials. Unlike dimethylformamide and N-methylpyrrolidone, which are the most commonly employed solvents. Our reaction conditions have been tested on three different ArDPPs (Ar = thiophene, phenyl and 4-methoxyphenyl) with a variety of linear and branched alkyl reagents. The results show similar and improved results in comparison with the published reports while reducing the waste and hazard of the reaction, as well as simplifying the purification of the products in many cases. Overall this method has lower environmental impact, is more cost effective and requires neither the use of dry solvent nor inert atmosphere