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

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Mechanofluorochromic materials, which are dependent on changes in physical molecular packing modes, have attracted considerable interest over the past ten years. In this review, recent progress in the area of pure organic mechanofluorochromism is summarized, and majority of the reported organic mechanofluorochromic systems are discussed, along with their derived structure–property relationships. The existence of a structural relationship between aggregation-induced emission compounds and mechanofluorochromism is recognized based on our recent results, which considered aggregation-induced emission compounds as a well of mechanofluorochromic materials. The established structure–property relationship will guide researchers in identifying and synthesizing more mechanofluorochromic materials.

Recent advances in organic mechanofluorochromic materials

Functional π-Gelators and Their Applications

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

A novel design principle for materials showing piezochromic luminescence is proposed. Amide-substituted tetraphenylpyrene C6TPPy, composed of a planar fluorescent core and multiple hydrogen-binding sites, displays a remarkable change and restoration of its luminescence color by pressing with a spatula and heating, respectively.

Material design for piezochromic luminescence: hydrogen-bond-directed assemblies of a pyrene derivative.

Nucleobases are nitrogenous heterocyclic compounds and have high ability to form directionally controlled multiple intermolecular interaction, i.e., in-plane multiple hydrogen-bonding interactions and stacking interactions perpendicular to the plane. Here the recent development of nucleobase-containing low molecular mass gelators in aqueous and organic systems is reviewed, and the self-assemblies of nucleobase-containing small molecules and their arrangement within the gel are discussed from the molecular, and mesoscopic to the macroscopic level in regard to becoming a macroscale three-dimensional network. Brief overview of the nucleoside-containing supramolecular materials are also presented.

Nucleobase-containing gelators.

The isomerization behaviors of 2-(phenylazo)imidazole (Pai-H) and 1-N-methyl-2-(phenylazo)imidazole (Pai-Me) have been investigated. The crystal structure of trans-Pai-Me was determined, revealing that key structures around the azo group are nearly identical among azobenzene, Pai-H, and Pai-Me. Pai-Me undergoes reversible cis/trans photoisomerization, whereas Pai-H responds poorly to irradiation. The quantum yields of trans-to-cis isomerization of Pai-Me on 454 and 355 nm excitation are 0.35 ± 0.03 and 0.25 ± 0.03, respectively, in toluene. The wavelength-dependent isomerization quantum yield is well-known for azobenzene, but these values are substantially higher than those of azobenzene. The activation energy of thermal cis-to-trans isomerization of Pai-Me in toluene is 79.0 ± 3.5 kJ mol-1, which is lower than that of azobenzene by 15 kJ mol-1. The thermal cis-to-trans isomerization of Pai-H is even faster. Density functional theory calculations were performed, revealing that the energy gaps between the ...

Photochromism of 2-(Phenylazo)imidazoles

A series of amide and ester derivatives of 1,3,6,8-tetraphenylpyrene (TPPy) were prepared, and their solid-state luminescence, molecular packing, and piezochromic responses were studied in order to improve and refine the design concept of piezochromic luminescent materials based on the use of multiple hydrogen bonds and close packing of disk-shaped aromatic cores as competing factors in the control of molecular packing. The amide derivative of TPPy having hexyl side chains (1b) showed a sensitive luminescence response at a relatively low applied pressure, which was ascribed to the hydrogen bond-directed H-type columnar packing. Application of higher pressure induced considerable destruction of the hydrogen bond-directed structure, leading to the state where close packing was the overriding factor directing the molecular assembly and showed similar piezochromic response to that of the ester derivative. Based on the results, the role of the amide hydrogen bonds and the side chains was discussed in detail.

Isao Yoshikawa

Papers

Material design for piezochromic luminescence: hydrogen-bond-directed assemblies of a pyrene derivative.

Nucleobase-containing gelators.

Photochromism of 2-(Phenylazo)imidazoles

Piezochromic luminescence of amide and ester derivatives of tetraphenylpyrene—role of amide hydrogen bonds in sensitive piezochromic response

Highly Stable Giant Supramolecular Vesicles Composed of 2D Hydrogen-Bonded Sheet Structures of Guanosine Derivatives