Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c‐axes) of the crystal are contracted upon elongation along the long axis (a‐axis). Moreover, we found that the Poisson's ratios along the b‐axis and c‐axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c‐axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other. 相似文献
Colloidal particles may be considered as building blocks for materials, just like atoms are the bricks of molecules, macromolecules, and crystals. Periodic arrays of colloids (colloidal crystals) have attracted much interest over the last two decades, largely because of their unique photonic properties. The archetype opal structures are based on close-packed arrays of spheres of submicrometer diameter. Interest in structuring materials at this length scale, but with more complex features and ideally by self-assembly processes, has led to much progress in controlling features of both building blocks and assemblies. The necessary ingredients include colloids, colloidal clusters, and colloidal \"molecules\" which have special shapes and the ability to bind directionally, the control over short-range and long-range interactions, and the capability to place and orientate these bricks. This Review highlights recent experimental and theoretical progress in the assembly of colloids larger than 50 nm. 相似文献
Systematic variation of the molecular symmetry in a photochromic system based on a 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene group, connected by decyl spacers to two cyanobiphenyl groups as mesogens, allows for a systematic investigation of the correlations between molecular shape and symmetry, electronic effects, photochromic conversion and liquid-crystalline properties. 相似文献
A series of modular mesogenic salts based on the combination of anionic 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (F‐BODIPY) 2,6‐disulfonate dyes and trialkoxybenzyl‐functionalised imidazolium cations has been designed and synthesised. Each salt contains a rigid dianionic BODIPY core associated with two imidazolium cations functionalised by 1,2,3‐trialkoxybenzyl (alkyl=n‐C8, n‐C12 or n‐C16) units or, in one case, with imidazolium cations functionalised by a trialkylgallate (3,4,5‐trialkoxybenzoate) unit in which the 3,5‐dialkyl groups are terminated with a polymerisable acrylate entity. All these compounds were highly fluorescent in solution with quantum yields ranging from 54 to 62 %. In the solid state, the width of the emission band observed at around 650 nm is a clear signature of aggregation. With the trialkoxybenzylimidazolium cations, polarised optical microscopy (POM) and X‐ray scattering experiments showed that columnar mesophases were formed. Differential scanning calorimetry (DSC) studies confirmed the mesomorphic behaviour from room temperature to about 130 °C for salts with alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of the BODIPY unit was maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The salt containing the gallate‐functionalised imidazolium cations showed no mesomorphism but the acrylate terminal units could be used to engender photoinitiated polymerisation thereby allowing the material to be immobilised on glass plates. The polymerisation process was followed by FTIR spectroscopy and the fixed and patterned films were highly fluorescent with a solid‐state emission close to that of the complex in the solid state. 相似文献
Always on the move : Molecular dynamics of perylene cores in columnar structures influences the processability and self‐healing of these materials. A combination of X‐ray scattering and advanced solid‐state NMR methods show that these systems have restricted angular mobility of the cores even in the frozen phase, and a cooperative spiral type of motion in the liquid crystalline phase (see picture).
Molecular crystals of π-conjugated molecules are of great interest as the highly ordered dense packing offers superior charge and exciton transport compared with its amorphous counterparts. However, integration into optoelectronic devices remains a major challenge owing to its inherently brittle nature. Herein, control over the mechanical conformity in single crystals of pyridine-appended thiazolothiazole derivatives is reported by modulating the molecular packing through interaction engineering. Two polymorphs were prepared by achieving control over the thermodynamic/kinetic factors of crystallization; one of the polymorphs exhibits elastic bending whereas the other is brittle. The control over the bending ability was achieved by forming co-crystals with hydrogen/halogen bond donors. A seamless extended crisscross pattern with respect to the bend plane through a ditopic hydrogen-bonding motif showed the highest compliance towards mechanical bending, whereas the co-crystals with a layered crisscross arrangement with segregated layers of co-formers exhibit slightly lower bending conformity. These results update the rationale behind the plastic/elastic bending in molecular crystals. The co-crystals of ditopic halogen bond co-assemblies are particularly appealing for waveguiding applications as the co-crystals blend high mechanical flexibility and luminescence properties. The hydrogen bonded co-crystals are non-emissive in nature owing to excited state proton transfer dynamics. The rationale behind the fluorescence properties of these materials was also established from DFT calculations in a quantum mechanics/molecular mechanics (QM/MM) framework. 相似文献
Self‐assembly has been relied upon for molecular alignment in many advanced technological applications. However, although effective, it is inherently limited in its capability for optimization. Despite the potential benefits, the seemingly fundamental strategy of external orientation control has yet to be realized. Herein we demonstrate an approach that allows control of the orientation of small molecules covalently bound to a surface. The method exploits an alignment relay technique, passing alignment information through a liquid‐crystal medium to small molecules to control surface functionalization events. The method is technically simple and can be carried out on a bench top without the need for specialized equipment. Moreover, we demonstrate the utility of the resulting surfaces to address two long‐standing problems in nanoscience: the sorting and alignment of single‐walled carbon nanotubes. This new method enabled significant alignment of the nanotubes as well as length and diameter sorting. 相似文献
This paper describes the polyfunctional intermediates for the preparation of various anisotropic and liquid-crystalline compounds with different combinations of cyclic, bridge, terminal fragments and lateral substituents. Both chiral and nonchiral nematic, smectic mesomorphic and anisotropic compounds can be prepared by the transformations of the corresponding 3,6-disubstituted cyclohex-2-enones, trans-2,5-disubstituted cyclohexanones, 3,5-disubstitiuted 2-isoxazolines, substituted cyclohex-2-enonyl 2-isoxazolines, 1,2-disubstitiuted cyclopropanols and substituted unsaturated epoxyketones. 相似文献
Elastic metal–organic materials (MOMs) capable of multiple stimuli-responsiveness based on dual-stress and thermally responsive triple-helix coordination polymers are presented. The strong metal-coordination linkage and the flexibility of organic linkers in these MOMs, rather than the 4 Å stacking interactions observed in organic crystals, causes the helical chain to act like a molecular spring and thus accounts for their macroscopic elasticity. The thermosalient effect of elastic MOMs is reported for the first time. Crystal structure analyses at different temperatures reveal that this thermoresponsiveness is achieved by adaptive regulation of the triple-helix chains by fine-tuning the opening angle of flexible V-shaped organic linkers and rotation of its lateral conjugated groups to resist possible expansion, thus demonstrating the vital role of adaptive reorganization of triple-helix metal–organic chains as a molecular spring-like motif in crystal jumping. 相似文献
