Signaling Recognition Events with Fluorescent Sensors and Switches.

Diarylethenes for Memories and Switches

The miniaturization of components used in the construction of working devices is being pursued currently by the large-downward (top-down) fabrication. This approach, however, which obliges solid-state physicists and electronic engineers to manipulate progressively smaller and smaller pieces of matter, has its intrinsic limitations. An alternative approach is a small-upward (bottom-up) one, starting from the smallest compositions of matter that have distinct shapes and unique properties-namely molecules. In the context of this particular challenge, chemists have been extending the concept of a macroscopic machine to the molecular level. A molecular-level machine can be defined as an assembly of a distinct number of molecular components that are designed to perform machinelike movements (output) as a result of an appropriate external stimulation (input). In common with their macroscopic counterparts, a molecular machine is characterized by 1) the kind of energy input supplied to make it work, 2) the nature of the movements of its component parts, 3) the way in which its operation can be monitored and controlled, 4) the ability to make it repeat its operation in a cyclic fashion, 5) the timescale needed to complete a full cycle of movements, and 6) the purpose of its operation. Undoubtedly, the best energy inputs to make molecular machines work are photons or electrons. Indeed, with appropriately chosen photochemically and electrochemically driven reactions, it is possible to design and synthesize molecular machines that do work. Moreover, the dramatic increase in our fundamental understanding of self-assembly and self-organizational processes in chemical synthesis has aided and abetted the construction of artificial molecular machines through the development of new methods of noncovalent synthesis and the emergence of supramolecular assistance to covalent synthesis as a uniquely powerful synthetic tool. The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives. After analyzing a few important examples of natural molecular machines, the most significant developments in the field of artificial molecular machines are highlighted. The systems reviewed include 1) chemical rotors, 2) photochemically and electrochemically induced molecular (conformational) rearrangements, and 3) chemically, photochemically, and electrochemically controllable (co-conformational) motions in interlocked molecules (catenanes and rotaxanes), as well as in coordination and supramolecular complexes, including pseudorotaxanes. Artificial molecular machines based on biomolecules and interfacing artificial molecular machines with surfaces and solid supports are amongst some of the cutting-edge topics featured in this review. The extension of the concept of a machine to the molecular level is of interest not only for the sake of basic research, but also for the growth of nanoscience and the subsequent development of nanotechnology.

Artificial Molecular Machines.

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators

Spectroscopic properties and design of highly luminescent lanthanide coordination complexes

Thermally irreversible photochromic systems. Reversible photocyclization of 1,2-bis(thiazolyl)perfluorocyclopentenes

This review article covers recent topics of a calixarene family concerning their stereochemistry, complexation with metal ions and organic guests, and other topics As stereochemistry of calixarenes, the restriction of flipping motions of the composed benzene units of calix[4]-, [5]-, [6]arenes is summarized In Recognition of Calixarenes, the selective recognition of alkali metal cations utilizing calixcrowns is a main subject in metal cation recognition Concerning with recognition of metal cations and organic molecules, the ‘reading-out’ systems of recognition phenomena are summarized The complexation of calix[8]arene with fullerene, which was discovered as serendipity and will be very useful as a new fullerene purification method is also reported

Recent Topics on Functionalization and Recognition Ability of Calixarenes: The ‘Third Host Molecule’

The effect of inclusion of diarylethenes in cyclodextrin cavities on cyclization quantum yields and on circular dichroism (CD) spectral changes by photoirradiation was studied. The addition of β- and γ-cyclodextrins to an aqueous solution of the open-ring form of 2,2‘-dimethyl-3,3‘-(perfluorocyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a) increased the ratio of the antiparallel conformation. The enrichment of antiparallel conformation caused an increase in the photocyclization quantum yield of 1a. The CD spectral intensity of the mixtures of 1a or 2,2‘,4,4‘-tetramethyl-3,3‘-(perfluorocyclopentene-1,2-diyl)bis(thiophen-5-yl-(phenyl-4-sulfonate)) (2a) and cyclodextrins in aqueous solution increased with the increasing concentration of cyclodextrins. The induced CD spectrum of 1 in β-cyclodextrin reversibly changed from negative to positive by UV irradiation. The spectral change was attributed to the change in the direction of transition moment of 1 in the cavity.

Photochromism of Dithienylethenes Included in Cyclodextrins

Alkali metal ion extraction was carried out using photochromic dithienylethene having two benzo-12-crown-4 ethers (1), benzo-15-crown-5 ethers (2), or benzo-18-crown-6 ethers moieties (3) and bis(benzothienyl)ethene having two benzo-18-crown-6 ether moieties (4) Two crown ether moieties of the open-ring form captured large metal ions cooperatively like tweezers, while the photogenerated closed-ring form released the ions The reduced affinities for metal picrates were fully recovered by irradiation with visible light (>480 nm) The 1H NMR spectrum measurement of the solutions (CDCl3/CD3CN: 5/1) containing both alkali metal picrates and 2 or 3 confirmed that the large alkali metal ions were captured by the two intramolecular crown ethers

Photoresponsive Tweezers for Alkali Metal Ions. Photochromic Diarylethenes Having Two Crown Ether Moieties

Syntheses and ion selectivities of tri-amide derivatives of hexahomotrioxacalix[3]arene. Remarkably large metal template effect on the ratio of cone vs. Partial-cone conformers

Michinori Takeshita

Papers

Thermally irreversible photochromic systems. Reversible photocyclization of 1,2-bis(thiazolyl)perfluorocyclopentenes

Recent Topics on Functionalization and Recognition Ability of Calixarenes: The ‘Third Host Molecule’

Photochromism of Dithienylethenes Included in Cyclodextrins

Photoresponsive Tweezers for Alkali Metal Ions. Photochromic Diarylethenes Having Two Crown Ether Moieties

Syntheses and ion selectivities of tri-amide derivatives of hexahomotrioxacalix[3]arene. Remarkably large metal template effect on the ratio of cone vs. Partial-cone conformers