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Journal ArticleDOI

Elastic and bendable caffeine cocrystals: implications for the design of flexible organic materials.

08 Oct 2012-Angewandte Chemie (WILEY‐VCH Verlag)-Vol. 51, Iss: 41, pp 10319-10323
TL;DR: A remarkably flexible, elastically bendable cocrystal solvate 1 is reported, formed from caffeine, 4-chloro-3-nitrobenzoic acid, and methanol in a 1:1:< 1 ratio (Figure 1).
Abstract: Molecular crystals are among the most ancient and highly investigated materials in chemistry. However, mechanical properties of these materials have remained relatively unexplored despite their unique applications in optoelectronics, mechanical actuators, artificial muscles, pharmaceuticals, and explosives. Conserving the orientational order of molecules and bonds is important for efficient charge transport and for the lifetime of organic light-emitting diodes, transistors, and solar cells. Hence, the realization of high-performance materials with excellent self-healing capabilities or efficient stress dissipating behaviors is attractive. For this reason, the remarkable properties displayed by natural fibres such as spider silk, muscle protein titin, cytoskeleton microtubules, etc. have recently sparked tremendous interest in establishing a reliable structure–property correlation to guide the design of their mimics for various applications. A good starting point for achieving such a goal is to study much simpler and easy-to-characterize organic crystals, which selfassemble through the same noncovalent interactions. It remains a challenge to simultaneously achieve both flexibility and crystallinity in organic materials because crystallinity positively correlates with brittleness. For example, compared to highly ordered molecular crystals, liquid crystals show greater flexibility, but are less crystalline. Desiraju and co-workers showed irreversible mechanical bending in organic crystals as mediated by the movement of molecular sheets through weak interactions between them. The plastic deformation disrupts the long-range order permanently. It was also shown that reversible molecular movements in organic crystals (e.g., in photomechanical bending), can perform work in devices. Herein we report a remarkably flexible, elastically bendable cocrystal solvate 1, formed from caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB), and methanol in a 1:1:< 1 ratio (Figure 1). The cocrystal solvate 1 retains a high internal order through an efficient stress dissipation mechanism, and hence is important in the context of crystal engineering and for the design of flexible organic materials. The single crystals of 1 could be obtained from a 1:1 molar solution of CAF and CNB in methanol by using a slow evaporation method (Figure 1). H NMR and thermogravimetric (TG) analyses have confirmed the presence of CAF, CNB, and methanol molecules in a 1:1:< 1 ratio within the lattice (see Figures S1 and S2 in the Supporting Information). The typically long needle crystals of 1 grow along the a axis (Figure 1 and Figure S4). When a straight crystal, having about a 0.1 mm thickness and 5 mm length, was pushed with a metal pin while being held with a pair of forceps (tweezers) from the opposite end, it transformed into a bent shape without breaking (Figure 2a–d and Figure S5). Further, it could be made into a loop by joining the two ends with a smooth curve (see Videos S1–S3 in the Supporting Information). Upon withdrawal of the force, the crystal quickly Figure 1. Single-crystal preparation of the cocrystal solvate 1 from a methanol solution of caffeine and 4-chloro-3-nitrobenzoic acid.
Citations
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Journal ArticleDOI
TL;DR: This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design.
Abstract: How do molecules aggregate in solution, and how do these aggregates consolidate themselves in crystals? What is the relationship between the structure of a molecule and the structure of the crystal it forms? Why do some molecules adopt more than one crystal structure? Why do some crystal structures contain solvent? How does one design a crystal structure with a specified topology of molecules, or a specified coordination of molecules and/or ions, or with a specified property? What are the relationships between crystal structures and properties for molecular crystals? These are some of the questions that are being addressed today by the crystal engineering community, a group that draws from the larger communities of organic, inorganic, and physical chemists, crystallographers, and solid state scientists. This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design. It also provides a look to the future from the viewpoint of the author, and indicates some directions in which this field might be moving.

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Cites background from "Elastic and bendable caffeine cocry..."

  • ...The most extreme example of elastic cocrystal behaviour was seen in the caffeine·4-chloro-3-nitrobenzoic acid methanol solvate [140]....

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Journal ArticleDOI
TL;DR: Through nanoindentation it is possible to correlate molecular-level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid-state reactivity.
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References
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TL;DR: With properly chosen parameters, the model provides a remarkably accurate ``roadmap'' of nanotube behavior beyond Hooke's law.
Abstract: Carbon nanotubes subject to large deformations reversibly switch into different morphological patterns. Each shape change corresponds to an abrupt release of energy and a singularity in the stress-strain curve. These transformations, simulated using a realistic many-body potential, are explained by a continuum shell model. With properly chosen parameters, the model provides a remarkably accurate ``roadmap'' of nanotube behavior beyond Hooke's law.

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Journal ArticleDOI
10 Aug 2001-Science
TL;DR: Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes, demonstrating that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.
Abstract: Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes. The discotic liquid crystal hexa-peri-hexabenzocoronene was used in combination with a perylene dye to produce thin films with vertically segregated perylene and hexabenzocoronene, with large interfacial surface area. When incorporated into diode structures, these films show photovoltaic response with external quantum efficiencies of more than 34 percent near 490 nanometers. These efficiencies result from efficient photoinduced charge transfer between the hexabenzocoronene and perylene, as well as from effective transport of charges through vertically segregated perylene and hexabenzocoronene pi systems. This development demonstrates that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.

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Journal ArticleDOI
TL;DR: In this article, a review of π-conjugated polymeric semiconductors for organic thin-film (or field effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.
Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.

2,076 citations

Journal Article
TL;DR: The Atom-Atom Potential Method and the Close-Packing Model for Molecular Crystals as mentioned in this paper have been used to predict the crystal structures of organic molecules using the Kitaigorodskii model.
Abstract: 1 Molecular Crystals and Crystal Engineering Crystal engineering Why design crystal structures of organic molecules? Some extensions Conclusions 2 The Atom-Atom Potential Method and the Close-Packing Model for Molecular Crystals Intermolecular forces in crystals The atom-atom potential method The close-packing model of Kitaigorodskii Crystal structure prediction Conclusions 3 Crystallographic Databases and the Recognition of Intermolecular Patterns The nature and growth of crystallographic information The Cambridge structural database Intermolecular patterns in crystals Conclusions 4 Structures Based Mostly on van der Waals Forces Non-bonded interactions involving carbon and hydrogen atoms Effects of van der Waals forces on crystal packing Occupied and unoccupied volumes in crystals Conclusions 5 Some Structures Based on Hydrogen Bonding Introduction Rationalisation of hydrogen bonding patterns The role of C-HO interactions in determining crystal structures Other types of hydrogen bonding in crystals Conclusions 6 Structures Based on Intermolecular Contacts to Halogen Atoms The nature of halogenhalogen forces The geometry of halogenhalogen interactions Design of halogenhalogen stabilised crystal structures Contacts between halogen and non-halogen atoms Conclusions 7 Structures Based on Intermolecular Contacts to Sulphur The nature of sulphurheteroatom contacts Crystal design and engineering Conclusion 8 Designing Non-Centrosymmetric Crystals Introduction Some properties and applications of non-centrosymmetric crystals Methods of crystal design Non-centrosymmetry in other organised media Conclusions 9 Structures Based on Interactions Between Distinct Molecular Species: Solid Solutions, Donor-Acceptor Complexes and Clathrates Design of crystal structures of molecular complexes 10 Polymorphism - The Nemesis of Crystal Design? Polymorphism and crystal structure design 11 Conclusions Index

1,529 citations


"Elastic and bendable caffeine cocry..." refers background in this paper

  • ...The cocrystal solvate 1 retains a high internal order through an efficient stress dissipation mechanism, and hence is important in the context of crystal engineering([9]) and for the design of flexible organic materials....

    [...]

Journal ArticleDOI
TL;DR: Among the topics discussed are the nature of intermolecular interactions and their role in crystal design, the sometimes diverging perceptions of the geometrical and chemical models for a molecular crystal, the relationship of these models to polymorphism, knowledge-based computational prediction of crystal structures, and efforts at mapping the pathway of the crystallization reaction.
Abstract: Crystal engineering, the design of molecular solids, is the synthesis of functional solid-state structures from neutral or ionic building blocks, using intermolecular interactions in the design strategy. Hydrogen bonds, coordination bonds, and other less directed interactions define substructural patterns, referred to in the literature as supramolecular synthons and secondary building units. Crystal engineering has considerable overlap with supramolecular chemistry, X-ray crystallography, materials science, and solid-state chemistry and yet it is a distinct discipline in itself. The subject goes beyond the traditional divisions of organic, inorganic, and physical chemistry, and this makes for a very eclectic blend of ideas and techniques. The purpose of this Review is to highlight some current challenges in this rapidly evolving subject. Among the topics discussed are the nature of intermolecular interactions and their role in crystal design, the sometimes diverging perceptions of the geometrical and chemical models for a molecular crystal, the relationship of these models to polymorphism, knowledge-based computational prediction of crystal structures, and efforts at mapping the pathway of the crystallization reaction.

1,227 citations