Sussman B.J.,NRC Steacie Institute for Molecular Sciences
American Journal of Physics | Year: 2011
The dynamic Stark effect is the quasistatic shift in energy levels due to the application of optical fields. The effect is in many ways similar to the static Stark effect. However, the dynamic Stark effect can be applied on rapid time scales and with high energies, comparable to those of atoms and molecules themselves. The dynamic Stark effect due to nonresonant laser fields is used in a myriad of contemporary experiments to hold and align molecules, to shape potential energy surfaces, and to make rapid transient birefringence. Five approaches of increasing sophistication are used to describe the dynamic Stark effect. One application, molecular alignment, is summarized and a comparison is made between the dynamic Stark effect and Stokes light generation in a Raman scattering process. © 2011 American Association of Physics Teachers.
O'Dell L.A.,NRC Steacie Institute for Molecular Sciences
Progress in Nuclear Magnetic Resonance Spectroscopy | Year: 2011
Highlights: Experimental methods for the direct detection of 14N are surveyed. Advantages, disadvantages and practicalities of each technique are discussed. Includes single-crystal, ultra-wideline, MAS and overtone spectroscopy. © 2011 Published by Elsevier B.V. All rights reserved.
McKellar A.R.W.,NRC Steacie Institute for Molecular Sciences
Journal of Molecular Spectroscopy | Year: 2010
Most applications of synchrotron radiation lie in the ultraviolet and X-ray region, but it also serves as a valuable continuum source of infrared (IR) light which is much brighter (i.e. more highly directional) than that from normal thermal sources. The synchrotron brightness advantage was originally exploited for high spatial resolution spectroscopy of condensed-phase samples. But it is also valuable for high spectral resolution of gas-phase samples, particularly in the difficult far-IR (terahertz) range (1/λ ≈ 10-1000 cm -1). Essentially, the synchrotron replaces the usual thermal source in a Fourier transform IR spectrometer, giving a increase of up to two (or even more) orders of magnitude in signal at very high-resolution. Following up on pioneering work in Sweden (MAX-lab) and France (LURE), a number of new facilities have recently been constructed for high-resolution gas-phase IR spectroscopy. In the present paper, this new field is reviewed. The advantages and difficulties associated with synchrotron IR spectroscopy are outlined, current and new facilities are described, and past, present, and future spectroscopic results are summarized. Crown Copyright © 2010 Published by Elsevier Inc. All rights reserved.
Lofgreen J.E.,University of Toronto |
Moudrakovski I.L.,NRC Steacie Institute for Molecular Sciences |
Ozin G.A.,University of Toronto
ACS Nano | Year: 2011
We have prepared molecularly imprinted mesoporous organosilica (MIMO) using a semicovalent imprinting technique. A thermally reversible covalent bond was used to link a bisphenol A (BPA) imprint molecule to a functional alkoxysilane monomer at two points to generate a covalently bound imprint precursor. This precursor was incorporated into a cross-linked periodic mesoporous silica matrix via a typical acid-catalyzed, triblock copolymer-templated, sol-gel synthesis. Evidence of imprint sites buried in the pore walls was found through careful characterization of the imprinted material and its comparison to similarly prepared non-imprinted mesoporous organosilica (NIMO) and pure periodic mesoporous silica (PMS). After thermal treatment, the imprinted material (MIMO-ir) removed more than 90% of appropriately sized bisphenol species from water, yet showed significantly lower binding for both smaller and larger molecules containing phenol moieties. Identically treated NIMO-ir showed much poorer retention behavior than MIMO-ir for the same bisphenol species and behaved only slightly better than PMS-ir. © 2011 American Chemical Society.
Zgierski M.Z.,NRC Steacie Institute for Molecular Sciences |
Fujiwara T.,University of Akron |
Lim E.C.,University of Akron
Accounts of Chemical Research | Year: 2010
Photosynthesis, which depends on light-driven energy and electron transfer in assemblies of porphyrins, chlorophylls, and carotenoids, is just one example of the many complex natural systems of photobiology. A fuller understanding of the spectroscopy and photophysics of simple aromatic molecules is central to elucidating photochemical processes in the more sophisticated assemblies of photobiology. Moreover, developing a better grasp of the photophysics of simple aromatic molecules will also enhance our ability to create and improve practical applications in photochemical energy conversion, molecular nanophotonics, and molecular electronics. In this Account, we present a concerted experimental and theoretical study of aromatic ethynes, aromatic nitriles, and fluorinated benzenes, illustrating the important roles that the low-lying πσ* state plays in the electronic relaxation of these aromatic compounds. Diphenylacetylene, 4-dialkylaminobenzonitriles, 4-dialkylaminobenzethynes, and fluorinated benzenes exhibit fluorescence that strongly quenches as the excitation energy is increased for gas-phase systems and at elevated temperatures in solution. Much of this interesting photophysical behavior can be attributed to the presence of a dark intermediate state that crosses the fluorescent ππ* state. Our quantum chemistry calculations, as well as time-resolved laser spectroscopies, indicate that this dark intermediate state is the πσ* state that arises from the promotion of an electron from the π orbital of the phenyl ring to the σ* orbital localized in the C - X group (where X is CH and N) or on the C - X group (where X is a halogen). These crossings not only lead to the strong excitation energy and temperature dependence of fluorescence but also induce highly interesting πσ-mediated intramolecular charge transfer in 4- dialkylaminobenzonitriles. Most previous studies on the excited-state dynamics of organic molecules have examined aromatic hydrocarbons, nitrogen heterocycles, aromatic carbonyl compounds, and polyenes, which have low-lying excited states of ππ* character (hydrocarbons and polyenes) or nπ* and ππ* character (carbonyls and N-heterocycles). These studies have revealed important involvement of selection rules (promoting vibrational modes and spin-orbit coupling) and Franck-Condon factors for radiationless transitions, which have important effects on photophysical properties. The recent experimental and time-dependent density functional theory (TDDFT) calculations of aromatic ethynes, nitriles, and perfluorinated benzenes described in this Account demonstrate the importance of the bound excited state of a πσ* configuration in these molecules. © 2010 American Chemical Society.