Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes.

The use of NHCs for generating homoenolate species has gained widespread popularity in recent years. A number of highly stereoselective processes of NHC-homoenolates have emerged. Homoenolate reactions have also been employed as key steps in the total synthesis of a number of natural products. The use of compatible co-catalysts, improved NHC-catalyst design and the use of novel precursors for homoenolate generation are among the major developments in this area that were disclosed recently. This tutorial review organises and presents the advancements in this rapidly growing area of catalysis and in the process updates a previous account published in 2011 in this journal.

Recent advances in employing homoenolates generated by N-heterocyclic carbene (NHC) catalysis in carbon–carbon bond-forming reactions

Highly polarized compounds exhibiting intramolecular charge transfer (ICT) are used widely as nonlinear optical (NLO) materials and red emitters and in organic light emitting diodes. Low-molecular-weight donor/acceptor (D/A)-substituted ICT compounds are ideal candidates for use as the building blocks of hierarchically structured, multifunctional self-assembled supramolecular systems. This Account describes our recent studies into the development of functional molecular systems with well-defined self-assembled structures based on charge-transfer (CT) interactions. From solution (sensors) to the solid state (assembled structures), we have fully utilized intrinsic and stimulus-induced CT interactions to construct these functional molecular systems. We have designed some organic molecules capable of ICT, with diversity and tailorability, that can be used to develop novel self-assembled materials. These ICT organic molecules are based on a variety of simple structures such as perylene bisimide, benzothiadiazole, tetracyanobutadiene, fluorenone, isoxazolone, BODIPY, and their derivatives. The degree of ICT is influenced by the nature of both the bridge and the substituents. We have developed new methods to synthesize ICT compounds through the introduction of heterocycles or heteroatoms to the π-conjugated systems or through extending the conjugation of diverse aromatic systems via another aromatic ring. Combining these ICT compounds featuring different D/A units and different degrees of conjugation with phase transfer methodologies and solvent-vapor techniques, we have self-assembled various organic nanostructures, including hollow nanospheres, wires, tubes, and ribbonlike architectures, with controllable morphologies and sizes. For example, we obtained a noncentrosymmetric microfiber structure that possessed a permanent dipole along its fibers' long axis and a transition dipole perpendicular to it; the independent NLO responses of this material can be separated and tuned spectroscopically and spatially. The ready processability and intrinsically high NLO efficiency of these microfibers offer great opportunities for applications in photonic devices. We have also designed molecular sensors based on changes in the efficiency of the ICT process upon complexation of an analyte with the D or A moieties in the ICT compounds. Such sensors, which display evident Stokes shifts or changes in quantum yields or fluorescence lifetimes, have promise for applications in chemical and biological recognition and sensing. In this Account, we shed light on the structure-function relationships of these functional molecular systems with well-defined self-assembled structures based on ICT interactions. The encouraging results that we have obtained suggest that such self-assembled ICT molecular materials can guide the design of new nanostructures and materials from organic systems, and that these materials, across a range of compositions, sizes, shapes, and functionalities, can potentially be applied in the fields of electronics, optics, and optoelectronics.

Self-assembly of intramolecular charge-transfer compounds into functional molecular systems.

Acenes represent a series of molecules with intriguing physical and chemical properties for applications in organic electronics. Nevertheless, the stability and solubility issues associated with longer acenes are two major obstacles for their applications. In this Perspective, we summarize the major design principles for stabilizing acenes. A variety of stable acene based derivatives are included for discussion. Finally, we highlight some research areas where breakthroughs will be critical for the further development of acene based molecules and materials.

Recent Highlights and Perspectives on Acene Based Molecules and Materials

Synthesis and Structure Characterization of a Stable Nonatwistacene

A novel compound, 5,7,14,16-tetraphenyl-8:9,12:13-bisbenzo-hexatwistacene (TBH), has been successfully synthesized through a retro-Diels-Alder reaction. Single-crystal structure analysis indicated that TBH has a twisted configuration with a torsion angle of 27.34°. The HOMO-LUMO gap of TBH calculated from the difference between the half-wave redox potentials (E(1/2) (ox) =+0.40 eV and E(1/2)(red) =-1.78 eV) is 2.18 eV, which is in good agreement with the band gap (2.19 eV) derived from the UV/Vis absorption data. In addition, organic light-emitting devices using TBH as emitter have been fabricated. The results revealed that TBH is a promising red light-emitting candidate for applications in organic light-emitting diodes.

Synthesis, structure, and physical properties of 5,7,14,16-tetraphenyl-8:9,12:13-bisbenzo-hexatwistacene.

The title reaction employs catalytic amounts of N-heterocyclic carbene precursors and transforms a broad range of nitroalkenes, such as nitrodienes, nitroenynes, and nitrostyrenes, through reaction with a broad range of enals, into δ-nitroesters.

N‐Heterocyclic Carbene Catalyzed Homoenolate‐Addition Reaction of Enals and Nitroalkenes: Asymmetric Synthesis of 5‐Carbon‐Synthon δ‐Nitroesters

Organic nanowires of 9,10-dibromoanthracene (DBA) and 9,10-dicyanoanthracene (DCNA) were obtained by adding the THF solution of DBA/DCNA into water containing P123 surfactants. The as-prepared nanowires were characterized by UV-vis, fluorescence spectra, Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). We found that DBA and DCNA nanowires emitted green light rather than blue light for molecules in THF solution. The red-shift UV and fluorescent spectra of DBA and DCNA nanowires implied that these nanowires were formed through J-aggregation. The photoconducting study of DBA/DCNA nanowire-based network on rGO/SiO2/Si shows different photocurrent behaviors upon irradiation, which displayed that electron transfer from DCNA nanowire to rGO was stronger than that of DBA nanowires to rGO.

Li Ji

Papers

Synthesis and Structure Characterization of a Stable Nonatwistacene

Synthesis, structure, and physical properties of 5,7,14,16-tetraphenyl-8:9,12:13-bisbenzo-hexatwistacene.

N‐Heterocyclic Carbene Catalyzed Homoenolate‐Addition Reaction of Enals and Nitroalkenes: Asymmetric Synthesis of 5‐Carbon‐Synthon δ‐Nitroesters

Preparation, characterization, physical properties, and photoconducting behaviour of anthracene derivative nanowires.

A short and highly efficient synthesis of L-ristosamine and L-epi-daunosamine glycosides.