2.2. MOFs with Metal Active Sites 4614 2.2.1. Early Studies 4614 2.2.2. Hydrogenation Reactions 4618 2.2.3. Oxidation of Organic Substrates 4620 2.2.4. CO Oxidation to CO2 4626 2.2.5. Phototocatalysis by MOFs 4627 2.2.6. Carbonyl Cyanosilylation 4630 2.2.7. Hydrodesulfurization 4631 2.2.8. Other Reactions 4632 2.3. MOFs with Reactive Functional Groups 4634 2.4. MOFs as Host Matrices or Nanometric Reaction Cavities 4636

Engineering Metal Organic Frameworks for Heterogeneous Catalysis

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Hyperbranched polymers: from synthesis to applications

Advanced polyimide materials: Syntheses, physical properties and applications

The widespread use of molecular machines in biology has long suggested that great rewards could come from bridging the gap between synthetic molecular systems and the machines of the macroscopic world. In the last two decades, it has proved possible to design synthetic molecular systems with architectures where triggered large amplitude positional changes of submolecular components occur. Perhaps the best way to appreciate the technological potential of controlled molecular-level motion is to recognize that nanomotors and molecular-level machines lie at the heart of every significant biological process. Over billions of years of evolution, nature has not repeatedly chosen this solution for performing complex tasks without good reason. When mankind learns how to build artificial structures that can control and exploit molecular level motion and interface their effects directly with other molecular-level substructures and the outside world, it will potentially impact on every aspect of functional molecule and materials design. An improved understanding of physics and biology will surely follow.

The first steps on the long path to the invention of artificial molecular machines were arguably taken in 1827 when the Scottish botanist Robert Brown observed the haphazard motion of tiny particles under his microscope.1,2 The explanation for Brownian motion, that it is caused by bombardment of the particles by molecules as a consequence of the kinetic theory of matter, was later provided by Einstein, followed by experimental verification by Perrin.3,4 The random thermal motion of molecules and its implications for the laws of thermodynamics in turn inspired Gedankenexperiments (“thought experiments”) that explored the interplay (and apparent paradoxes) of Brownian motion and the Second Law of Thermodynamics. Richard Feynman’s famous 1959 lecture “There’s plenty of room at the bottom” outlined some of the promise that manmade molecular machines might hold.5,6 However, Feynman’s talk came at a time before chemists had the necessary synthetic and analytical tools to make molecular machines. While interest among synthetic chemists began to grow in the 1970s and 1980s, progress accelerated in the 1990s, particularly with the invention of methods to make mechanically interlocked molecular systems (catenanes and rotaxanes) and control and switch the relative positions of their components.7−24

Here, we review triggered large-amplitude motions in molecular structures and the changes in properties these can produce. We concentrate on conformational and configurational changes in wholly covalently bonded molecules and on catenanes and rotaxanes in which switching is brought about by various stimuli (light, electrochemistry, pH, heat, solvent polarity, cation or anion binding, allosteric effects, temperature, reversible covalent bond formation, etc.). Finally, we discuss the latest generations of sophisticated synthetic molecular machine systems in which the controlled motion of subcomponents is used to perform complex tasks, paving the way to applications and the realization of a new era of “molecular nanotechnology”.

1.1. The Language Used To Describe Molecular Machines
Terminology needs to be properly and appropriately defined and these meanings used consistently to effectively convey scientific concepts. Nowhere is the need for accurate scientific language more apparent than in the field of molecular machines. Much of the terminology used to describe molecular-level machines has its origins in observations made by biologists and physicists, and their findings and descriptions have often been misinterpreted and misunderstood by chemists. In 2007 we formalized definitions of some common terms used in the field (e.g., “machine”, “switch”, “motor”, “ratchet”, etc.) so that chemists could use them in a manner consistent with the meanings understood by biologists and physicists who study molecular-level machines.14

The word “machine” implies a mechanical movement that accomplishes a useful task. This Review concentrates on systems where a stimulus triggers the controlled, relatively large amplitude (or directional) motion of one molecular or submolecular component relative to another that can potentially result in a net task being performed. Molecular machines can be further categorized into various classes such as “motors” and “switches” whose behavior differs significantly.14 For example, in a rotaxane-based “switch”, the change in position of a macrocycle on the thread of the rotaxane influences the system only as a function of state. Returning the components of a molecular switch to their original position undoes any work done, and so a switch cannot be used repetitively and progressively to do work. A “motor”, on the other hand, influences a system as a function of trajectory, meaning that when the components of a molecular motor return to their original positions, for example, after a 360° directional rotation, any work that has been done is not undone unless the motor is subsequently rotated by 360° in the reverse direction. This difference in behavior is significant; no “switch-based” molecular machine can be used to progressively perform work in the way that biological motors can, such as those from the kinesin, myosin, and dynein superfamilies, unless the switch is part of a larger ratchet mechanism.14

Artificial Molecular Machines

Considerable progress has been made in organic photorefractive materials, since the first observation of photorefractive phenomena from organic materials. Within recent years, a large number of organic photorefractive materials, especially amorphous materials, have been developed based on polymeric composites, fully functional polymers and the multifunctional chromophore approach. Among these organic photorefractive materials, some of them containing carbazole components as a charge transporting function have been demonstrated to exhibit high performance photorefractive effects. The carbazole building blocks with charge transporting functionality or multifunctions play a very important role in photorefraction and have been widely used in the molecular design approach to new organic photorefractive materials. Based on carbazole functional building blocks, amorphous multifunctional chromophores, amorphous monolithic chromophores and amorphous dendrimers have also been developed as new types of organic photorefractive materials. This paper reviews the recent progress of organic photorefractive materials, especially organic photorefractive materials containing carbazole functional components.

Carbazole photorefractive materials

Department of Chemistry, Australian National UniVersityCanberra, ACT 0200, AustraliaPhotonics CooperatiVe Research Centre, Laser Physics CentreResearch School of Physical Sciences and EngineeringAustralian National UniVersityCanberra, ACT 0200, AustraliaFrontier Research ProgramThe Institute of Physical and Chemical Research (RIKEN)Hirosawa 2-1, Wako-shiSaitama 351-01, JapanCentre for Research on Molecular Electronics and PhotonicsLaboratory of Chemical and Biological DynamicsUniVersity of LeuVen, Celestijnenlaan 200DB-3001 LeuVen, BelgiumReceiVed August 18, 1998There has been considerable interest recently in the quadraticnonlinear optical (NLO) properties of molecules that possessoctopolar symmetry.

Organometallic Complexes for Nonlinear Optics 16. Second and Third Order Optical Nonlinearities of Octopolar Alkynylruthenium Complexes

New microporous coordination polymer affording guest-coordination sites at channel walls

Polymers containing in the chain backbone carbazoles substituted with two acceptor groups as nonlinear optical chromophores have been synthesized from 3,6-diformyl-9-heptylcarbazole and bis(cyanoac...

Synthesis and Characterization of Polymers Containing in the Chain Backbone Carbazoles Substituted with Two Acceptor Groups as Nonlinear Optical Chromophores

A novel organic nonlinear optical crystal, l‐pyrrolidone‐2‐carboxylic acid (l‐PCA), has been found to be phase matchable for second‐harmonic generation (SHG) and sum‐frequency mixing down to the UV range at room temperature Tunable radiation down to 266 nm was obtained The nonlinear coefficient d14 of l‐PCA for the fundamental wavelength of 532 nm was determined to be 032 pm/V The angular acceptance (the full width at half‐maximum) of the type II phase‐matched SHG has also been measured to be 303 mrad cm which agreed with the calculated value This value is much larger than that of the type I phase‐matched SHG in β‐BBO

Tatsuo Wada

Papers

Carbazole photorefractive materials

Organometallic Complexes for Nonlinear Optics 16. Second and Third Order Optical Nonlinearities of Octopolar Alkynylruthenium Complexes

New microporous coordination polymer affording guest-coordination sites at channel walls

Synthesis and Characterization of Polymers Containing in the Chain Backbone Carbazoles Substituted with Two Acceptor Groups as Nonlinear Optical Chromophores

Ultraviolet generation at 266 nm in a novel organic nonlinear optical crystal: l‐pyrrolidone‐2‐carboxylic acid