Rigidity−Stability Relationship in Interlocked Model Complexes Containing Phenylene-Ethynylene-Based Disubstituted Naphthalene and Benzene

Structural rigidity has been found to be advantageous for molecules if they are to find applications in functioning molecular devices. In the search for an understanding of the relationship between the rigidity and complex stability in mechanically interlocked compounds, the binding abilities of two π-electron-rich model compounds (2 and 4), where rigidity is introduced in the form of phenylacetylene units, toward the π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT^(4+)), were investigated. 1,4-Bis(2-(2-methoxyethoxy)ethoxy)-2,5-bis(2-phenylethynyl)benzene 2 and 1,5-bis(2-(2-methoxyethoxy)ethoxy)- 2,6-bis(2-phenylethynyl)naphthalene 4 were synthesized, respectively, from the appropriate precursor dibromides 1 and 3 of benzene and naphthalene carrying two methoxyethoxyethoxy side chains. The rigid nature of the compounds 2 and 4 is reflected in the reduced stabilities of their 1:1 complexes with CBPQT^(4+). Binding constants for both 2 (100 M^(-1)) and 4 (140 M^(-1)) toward CBPQT^(4+) were obtained by isothermal titration microcalorimetry (ITC) in MeCN at 25 °C. Compounds 1-4 were characterized in the solid state by X-ray crystallography. The stabilization within and beyond these molecules is achieved by a combination of intra- and intermolecular [C-H· · · O], [C-H· · ·π], and [π-π] stacking interactions. The diethyleneglycol chains present in compounds 1-4 are folded as a consequence of both intra- and intermolecular hydrogen bonds. The preorganized structures in both precursors 1 and 3 are repeated in both model compounds 2 and 4. In the structures of compounds 2 and 4, the geometry of the rigid backbone is differentsthe two terminal phenyl groups are twisted with respect to the central benzenoid ring in compound 2 and roughly perpendicular to the plane central naphthalene core in compound 4. To understand the significantly decreased stabilities of these complexes toward rigid guest molecules, relative to more flexible systems, we performed density functional theory (DFT) calculations using the newly developed M06-suite of density functionals. We conclude that the reduced binding abilities are a consequence of electronic and not steric factors, originating from the extended delocalization of the aromatic system

D-π-D chromophores based on dithieno[3,2-b:2′,3'-d]thiophene (DTT) : potential application in the fabrication of solar cell

In this work, four stable dithieno[3,2-b:2′,3'-d]thiophene-based π-extended molecules were designed and synthesized via a Pd-catalysed Sonogashira coupling reaction. The structures of these symmetrical compounds, including dithieno[3,2-b:2′,3'-d]thiophene (DTT) as the π-center and various donor (D) groups, were determined on the basis of NMR spectral data, elemental analysis, and X-ray crystallography. The photo-physical properties of the DTT-based derivatives 2 were fully investigated in both solution and solid state. The notable optical features of their solid-state powders showed significant red-shift in comparison with the luminescence of their dilute dichloromethane solutions. These results combined with the theoretical calculations indicate that they are promising candidates for the several applications in electronic and optoelectronic devices, as well as organic dyes for solar cells

Synthesis of Alkynyl-substituted Camphor Derivatives and their Use in the Preparation of Paclitaxel-related Compounds.

Compounds containing two alkyne groups in close vicinity at the rigid skeleton of camphorsulfonamide show unique reactivities when treated with electrophiles or catalytic amounts of platinum(II), the product structures depending not only on the reagents but also on the substituents attached to the triple bonds. Cycloisomerisations with perfect atom economy lead to polycyclic heterocycles that resemble to some extent the AB ring system of paclitaxel. Herein, we present practical synthetic methods for the selective synthesis of precursor dialkynes bearing different substituents (alkyl, aryl) at the triple bonds, based on ketals or an imine as protecting groups. We show for isomeric dialkynes that the reaction cascade induced by Pt(II) includes ring annulation, sulfur reduction and ring enlargement. One isomeric dialkyne additionally allows for the isolation of a pentacyclic compound lacking the ring enlargement step, which we have proposed as a potential intermediate in the catalytic cycle

1,3,5-Tris(functionalised-phenylethynyl)benzene–metal complexes: synthetic survey of mesoporous coordination polymers and investigation of their carbonisation

A series of multicoordinate 1,3,5-tris(functionalised-phenylethynyl)benzenes (1–9) was synthesised, and coordination polymers were constructed from these organic linkers and copper ions in high yields. The carbonisation of the linkers 1–9 afforded a microporous carbon that shows type I adsorption–desorption isotherm. Although most of the coordination polymers prepared in this study turned out to be low porous materials, the coordination polymer 7e prepared from the reaction of 1,3,5-tris(4-carboxyphenylethynyl)benzene tripotassium salt (K37) and copper(II) nitrate was a microporous material in addition to the mesoporous materials (7c and 7d) prepared from the reaction of K37 with copper(II) acetate and copper(II) chloride, respectively. The carbonisation of the coordination polymers unexceptionally brought about an increase of micropore volume. A stepwise analysis of 7c pyrolysed at 350, 600, and 900 °C revealed that the mesoporosity hardly changed upon heat treatment, which in other words, demonstrates that microporosity could be successfully added to the mesoporous coordination polymer through the carbonisation process

Energy-harvesting materials

It is shown how key features of natural photosynthesis can be emulated in novel materials based on photoactive multichromophore arrays and crystals. A major consideration in the design of such systems is the means of channeling electronic excitation from sites of light absorption to centers where it is stored or released. Storage is often achieved by driving charge separation or, for the longer term, a more complex chemical reaction whilst rapid release is commonly associated with frequency up-converted emission. In each case channeling to the conversion site generally entails a multi-step energy transfer mechanism whose efficiency is determined by the arrangement and electronic properties of the array chromophores or ions, guided in the more complex systems by a spectroscopic gradient that promotes overall directionality. The functional cascade molecules known as photoactive dendrimers are exemplars of this approach. The latest developments involve new mechanisms for concerted excitation transfer in multichromophore systems, leading towards the tailoring and exploitation of optical nonlinearities for high intensity energy pooling applications

Functionalization of Pyrene To Prepare Luminescent Materials—Typical Examples of Synthetic Methodology

Pyrene-based π-conjugated materials are considered to be an ideal organic electro-luminescence material for application in semiconductor devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaics (OPVs), and so forth. However, the great drawback of employing pyrene as an organic luminescence material is the formation of excimer emission, which quenches the efficiency at high concentration or in the solid-state. Thus, in order to obtain highly efficient optical devices, scientists have devoted much effort to tuning the structure of pyrene derivatives in order to realize exploitable properties by employing two strategies, 1) introducing a variety of moieties at the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core. Over the past decades, our group has mainly focused on synthetic methodologies for functionalization of the pyrene core; we have found that formylation/acetylation or bromination of pyrene can selectly lead to functionalization at K-region by Lewis acid catalysis. Herein, this Minireview highlights the direct synthetic approaches (such as formylation, bromination, oxidation, and de-tert-butylation reactions, etc.) to functionalize the pyrene in order to advance research on luminescent materials for organic electronic applications. Further, this article demonstrates that the future direction of pyrene chemistry is asymmetric functionalization of pyrene for organic semiconductor applications and highlights some of the classical asymmetric pyrenes, as well as the latest breakthroughs. In addition, the photophysical properties of pyrene-based molecules are briefly reviewed. To give a current overview of the development of pyrene chemistry, the review selectively covers some of the latest reports and concepts from the period covering late 2011 to the present day

Structural Framework for Flight: NASA's Role in Development of Advanced Composite Materials for Aircraft and Space Structures

This serves as a source of collated information on Composite Research over the past four decades at NASA Langley Research Center, and is a key reference for readers wishing to grasp the underlying principles and challenges associated with developing and applying advanced composite materials to new aerospace vehicle concepts. Second, it identifies the major obstacles encountered in developing and applying composites on advanced flight vehicles, as well as lessons learned in overcoming these obstacles. Third, it points out current barriers and challenges to further application of composites on future vehicles. This is extremely valuable for steering research in the future, when new breakthroughs in materials or processing science may eliminate/minimize some of the barriers that have traditionally blocked the expanded application of composite to new structural or revolutionary vehicle concepts. Finally, a review of past work and identification of future challenges will hopefully inspire new research opportunities and development of revolutionary materials and structural concepts to revolutionize future flight vehicles

Extended π-conjugated pyrene derivatives: structural, photophysical and electrochemical properties

This article presents a set of extended π-conjugated pyrene derivatives, namely 1,3-di(arylethynyl)-7-tert-butylpyrenes, which were synthesized by a Pd-catalyzed Sonogashira coupling reaction of 1,3-dibromo-7-tert-butylpyrenes with the corresponding arylethynyl group in good yields. Despite the presence of the tert-butyl group located at the 7-position of pyrene, X-ray crystallographic analyses show that the planarity of the Y-shaped molecules still exhibits strong face-to-face π-π stacking in the solid state; all of the compounds exhibit blue or green emission with high quantum yields (QYs) in dichloromethane. DFT calculations and electrochemistry revealed that this category of compound possesses hole-transporting characteristics. In addition, with strong electron-donating (-N(CH₃)₂) or electron-withdrawing (-CHO) groups in 2 d or 2 f, these molecules displayed efficient intramolecular charge-transfer (ICT) emissions with solvatochromic shifts from blue to yellow (green) on increasing the solvent polarity. Furthermore, the compounds 2 d and 2 f possess strong CT characteristics