A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

Synthetic molecular motors and mechanical machines.

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.

Photoinduced motions in azo-containing polymers.

Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Analogues of mechanical devices that operate on the molecular level, such as shuttles, brakes, ratchets, turnstiles and unidirectional spinning motors, are current targets of both synthetic chemistry and nanotechnology. These structures are designed to restrict the degrees of freedom of submolecular components such that they can only move with respect to each other in a predetermined manner, ideally under the influence of some external stimuli. Alternating-current (a.c.) electric fields are commonly used to probe electronic structure, but can also change the orientation of molecules (a phenomenon exploited in liquid crystal displays), or interact with large-scale molecular motions, such as the backbone fluctuations of semi-rigid polymers. Here we show that modest a.c. fields can be used to monitor and influence the relative motion within certain rotaxanes, molecules comprising a ring that rotates around a linear 'thread' carrying bulky 'stoppers' at each end. We observe strong birefringence at frequencies that correspond to the rate at which the molecular ring pirouettes about the thread, with the frequency of maximum birefringence, and by inference also the rate of ring pirouetting giving rise to it, changing as the electric field strength is varied. Computer simulations and nuclear magnetic resonance spectroscopy show the ring rotation to be the only dynamic process occurring on a timescale corresponding to the frequency of maximum birefringence, thus confirming that mechanical motion within the rotaxanes can be addressed, and to some extent controlled, by oscillating electric fields.

Influencing intramolecular motion with an alternating electric field

A Switchable NLO Organic-Inorganic Compound Based on Conformationally Chiral Disulfide Molecules and Bi(III)I5 Iodobismuthate Networks

Towards the Calculations of Polarizabilities of Infinite Polymeric Chains.- Conjugated Polymers: On the Parallel Between the Electrical Conduction Mechanism and the Nonlinear Optical Response..- On the Calculation of the Hyperpolarizabilities of Organic Molecules by the Sum Over Virtual Excited States Method.- Impact of Electron Quantum Confinement on Optical Nonlinearities.- Structural and Electronic Properties of Push-Pull Conjugated Molecules: A Theoretical Investigation of p-Amino-p' Nitrodiphenylacetylene Compounds.- Polar and Non-Polar Organic Molecules, Crystals and Langmuir-Blodgett Films for Quadratic Nonlinear Optics.- Design Considerations for Multi Component Molecular-Polymeric Nonlinear Optical Materials.- Empirical Systematics of Molecular Quadratic Optical Polarizability.- Surface and Adsorbate Analysis by Second-Harmonic Generation.- New Molecular Design for Noncentrosymmetric Crystal Structures: Lambda shape Molecules for Frequency Doubling.- Study of Novel Class of Second Order Nonlinear Optical (NLO) Polyurethanes.- EFISH Studies of Stilbene- and Thiophene-Derivatives.- Surface Second Harmonic Generation in Total Reflection.- Second Order Hyperpolarisabilities and Conformations of Functionalized Copolymers.- NPNN: A New Ferromagnetic Optically Nonlinear Organic Compound.- Second Harmonic Generation from Amphiphilic Dyes at the Air-Water Interface.- Strategy for Optimization of Molecular Materials for Nonlinear Optics and Photonics.- Excited State Nonlinear Optics.- Influence of Conformation on Two-Photon Spectra of Polyalkylthiophene.- Advances in the Synthesis of Electroactive Materials and in the Characterisation of Mechanisms of NLO Activity..- Thiophene Based Conjugated Polymers: THG Spectroscopy and Transient Photogenerated Polaron Enhancement of Cubic Optical Nonlinearity.- Electronic Properties of Conjugated Polymers with Aromatic or Hetero-Aromatic Cycle.- Oriented Conjugated Polymers for Nonlinear Optics: Properties of a Liquid Crystalline Polyacetylene. Epitaxial Growth of a Polydiacetylene PDCH.- Third Order Nonlinear Optical Effects in Conjugated Polymers and Dye Systems.- Phase Conjugation under Picosecond Two-Photon Absorption in Polydiacetylenes.- Relaxation of One- and Two-Photon Excitations in a Polydiacetylene Red Form: Frequency and Phase Resolved Analysis.- Excited State Absorption and Optical Limiting in Solutions of Metallophthalocyanines.- Third Order Optical Nonlinearities in Metal Dithiolate Complexes.- Nonlinear Optical Studies of Transition Metal Containing Conjugated Organic Monomeric and Polymeric Systems.- Organic Thin Films for Quadratic Optics.- Poled Epoxy Polymers for Optoelectronics.- Poled Glassy Polymers and Metallated Macrocycles for Nonlinear Optics.- Electrooptic Organic Waveguides: Optical Characterization.- Optoelectronic Devices with Nonlinear Polymers.- Two-Photon Absorption in Polydiacetylene Based Waveguides: Its Origin and Its Consequences..- Second Harmonic Generation from Langmuir Layers and Langmuir-Blodgett Films.- An Adaptation of the Prism-Film Coupler Method Used to Study PVA/Chrysoidin Non-linear Waveguides.

Organic molecules for nonlinear optics and photonics

The permanent all-optical poling of an azo-aromatic acrylic copolymer is experimentally demonstrated by seeding preparation in a backward phase-conjugation geometry. The microscopic mechanism involves an orientational hole burning followed by orientational redistribution caused by trans-to-cis isomerization of the azo-dye chromophores. The characteristic kinetics of growth and decay of the noncentrosymmetry grating is monitored by second-harmonic generation.

Francois Kajzar

Papers

Influencing intramolecular motion with an alternating electric field

A Switchable NLO Organic-Inorganic Compound Based on Conformationally Chiral Disulfide Molecules and Bi(III)I5 Iodobismuthate Networks

Organic molecules for nonlinear optics and photonics

Light-induced second-harmonic generation in azo-dye polymers.

Conglomerate‐to‐True‐Racemate Reversible Solid‐State Transition in Crystals of an Organic Disulfide‐Based Iodoplumbate