Paul Rochon

Bio: Paul Rochon is an academic researcher from Royal Military College of Canada. The author has contributed to research in topics: Azobenzene & Diffraction grating. The author has an hindex of 45, co-authored 137 publications receiving 10051 citations. Previous affiliations of Paul Rochon include Helsinki University of Technology & Queen's University.

Optically induced surface gratings on azoaromatic polymer films

Abstract: The surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings. The gratings obtained are stable but can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed. Multiple gratings can be simultaneously written and gratings can be overwritten. Atomic force microscopy was used to investigate the gratings produced on the surfaces. Possible mechanisms responsible for the surface alteration are discussed.

Recent Developments in Aromatic Azo Polymers Research

Abstract: : The photochemical and thermal cis to trans isomerization of aromatic azo groups covalently bonded within polymers and its practical consequences as well as some other recent applications are reviewed. The kinetics and mechanism of the isomerization of azo polymers are briefly presented and then several recent developments in azo polymers research are discussed. They include liquid crystallinity, nonlinear optical properties, monolayer assemblies and the light induced birefringence and dichroism. Some of the phase transitions of liquid crystalline azo polymers can be induced photochemically by the azo groups isomerization. Second order optical nonlinearity can be obtained in polymers with donor and acceptor substituted azo groups. Using the Langmuir-Blodgett technique, azo polymer monolayers can be built and used as 'command surfaces' of liquid crystal films. The light induced birefringence is a reorientation phenonmenon which is a consequence of the trans-cis-trans isomerization. Future possible applications for a variety of practical devices, such as display devices, optical modulators, optical waveguides, holography, and reversible optical storage are mentioned. Azo polymers, Review, Optoelectronic and photonic applications

Mechanism of Optically Inscribed High-Efficiency Diffraction Gratings in Azo Polymer Films

Abstract: A series of amorphous azobenzene-containing polymers were cast as thin films and shown to produce both reversible volume diffraction gratings and high-efficiency surface gratings by laser irradiation at an absorbing wavelength. The latter process involves localized mass transport of the polymer chains to a high degree, as atomic force microscopy reveals surface profile depths near that of the original film thickness. A mechanism for this phenomenon is proposed which involves pressure gradients as a driving force, present due to different photochemical behaviors of the azo chromophores at different regions of the interference pattern. The phase addition of the two beams in the interference pattern leads to regions of high trans-cis-trans isomerization by the absorbing azo groups, bordered by regions of low isomerization. As the geometrical isomerization requires free volume in excess of that available in the cast films, the photochemical reaction in these areas produces a laser-induced internal pressure ab...

Model of laser-driven mass transport in thin films of dye-functionalized polymers

Abstract: Based on Newtonian fluid dynamic relations, a model is constructed to describe laser-induced mass transport in thin films of polymers containing isomerizable azobenzene chromophores, in which surface profile diffraction gratings can be inscribed with an interference pattern of coherent light. The Navier–Stokes equations for laminar flow of a viscous fluid are developed to relate velocity components in the film to pressure gradients in the polymer film, by definition of boundary layer conditions. This general laminar flow model is applicable to the formation of surface gratings through a variety of mechanisms. Considering the mechanism of an isomerization-driven free volume expansion to produce internal pressure gradients, a specific model is developed to describe polymer flow resulting from laser-induced isomerization of the bulky chromophores. This yields an expression relating the time evolution of the surface gratings to properties which could be varied experimentally, such as those of the irradiating ...

The Halogen Bond

Abstract: The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Synthetic molecular motors and mechanical machines.

Abstract: 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.

Artificial Molecular Machines

Abstract: 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