Polymer thin films that emit and absorb circularly polarised light have been demonstrated with the promise of achieving important technological advances; from efficient, high-performance displays, to ...3D imaging and all-organic spintronic devices. However, the origin of the large chiroptical effects in such films has, until now, remained elusive. We investigate the emergence of such phenomena in achiral polymers blended with a chiral small-molecule additive (1-aza6helicene) and intrinsically chiral-sidechain polymers using a combination of spectroscopic methods and structural probes. We show that - under conditions relevant for device fabrication - the large chiroptical effects are caused by magneto-electric coupling (natural optical activity), not structural chirality as previously assumed, and may occur because of local order in a cylinder blue phase-type organisation. This disruptive mechanistic insight into chiral polymer thin films will offer new approaches towards chiroptical materials development after almost three decades of research in this area.
Real-space images of polymers with sub-molecular resolution could provide valuable insights into the relationship between morphology and functionality of polymer optoelectronic devices, but their ...acquisition is problematic due to perceived limitations in atomic force microscopy (AFM). We show that individual thiophene units and the lattice of semicrystalline spin-coated films of polythiophenes (PTs) may be resolved using AFM under ambient conditions through the low-amplitude (≤ 1 nm) excitation of higher eigenmodes of a cantilever. PT strands are adsorbed on hexagonal boron nitride near-parallel to the surface in islands with lateral dimensions ~10 nm. On the surface of a spin-coated PT thin film, in which the thiophene groups are perpendicular to the interface, we resolve terminal CH
-groups in a square arrangement with a lattice constant 0.55 nm from which we can identify abrupt boundaries and also regions with more slowly varying disorder, which allow comparison with proposed models of PT domains.
One of the great challenges in stereochemistry is the explanation of why some molecules resolve spontaneously while others do not. In this critical review the recent advances in the creation of ...chiral systems from achiral and racemic compounds in three-, two- and one-dimensional systems are discussed. There are some groups of molecules in some systems that do tend to display conglomerates, which may suggest that there are enantiophobic and enantiophilic molecules whose assembly is guided by the structural and thermodynamic properties of the systems in question.
A terbium double‐decker phthalocyanine complex has been prepared and characterized. The mesomorphism of the liquid‐crystalline complex is used as a tool to reversibly adjust its magnetic properties, ...thus allowing the coexistence of two different relaxation processes, which can be reversibly modified by simple thermal treatments, to be observed.
Stereochemistry and Twisted Crystals Killalea, Catherine E.; Amabilino, David B.
Israel journal of chemistry,
October 2021, Letnik:
61, Številka:
9-10
Journal Article
Recenzirano
Odprti dostop
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.
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.
Nanocorrals created in situ can selectively induce the formation of one of two concomitant polymorphs, which otherwise appear simultaneously at the interface of 1‐phenyloctane/highly‐oriented pyrolytic graphite.
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