Fluorescence spectroscopy intermolecular interactions

A short excursion into the physics and spectroscopy of intermolecular interactions is intended to illustrate the effects of fluorescence spectra change on the transition of dye molecules from liquid solvents to solid environments, on the change of polarity and hydration in these environments, and on the formation of excited-state complexes (excimers and exciplexes). 

Substantial evidence suggests that in highly asymmetric supercritical mixtures the local and bulk environment of a solute molecule differ appreciably. The concept of a local density enhancement around a solute molecule is supported by spectroscopic, theoretical, and computational investigations of intermolecular interactions in supercritical solutions. Here we make for the first time direct comparison between local density enhancements determined for the system pyrene in CO2 by two very different methods-fluorescence spectroscopy and molecular dynamics simulation. The qualitative agreement is quite satisfactory, and the results show great promise for an improved understanding at a molecular level of supercritical fluid solutions. 

Angus, S. Armstrong, B. de Reuck, K. M. eds., International Thermodynamic Tables of the Fluid State Carbon Dioxide. Pergamon Press, Oxford, 1976. Brennecke, J. F. Intermolecular Interactions in Supercritical Fluid Solutions from Fluorescence Spectroscopy. PhD Thesis, University of Illinois, Urbana, 1989. Brennecke, J. F. Eckert, C. A. AIChE J.. 1989, 35(9), 1409-1427. 

Bidimensional fluorescence spectra are commonly obtained in the three modes of emission, excitation, and synchronous-scan excitation, whereas tridimensional fluorescence (or total luminescence) spectra are obtained in the form of excitation-emission matrix (EEM) plots by measuring the fluorescence intensity emitted as a function of the wavelength over a range of excitation wavelengths. This technique allows to obtain more detailed information than that obtained by using conventional monodimensional fluorescence (Mobed et al., 1996). Fluorescence spectroscopy has provided valuable information on the molecular structure, functionalities, conformation, and intramolecular and intermolecular interactions of HS from organic amendments and unamended and amended soils (Senesi et al., 1990,1996, 2007 Mobed et al., 1996 Chen et al., 2003 Senesi and Plaza, 2007). 

In 1964, the spin echo experiment was extended to the optical regime by the development of the photon echo experiment (3,4). The photon echo began the application of coherent pulse techniques in the visible and ultraviolet portions of the electromagnetic spectrum. Since its development, the photon echo and related pulse sequences have been applied to a wide variety of problems including dynamics and intermolecular interactions in crystals, glasses, proteins, and liquids (5-8). Like the spin echo, the photon echo and other optical coherent pulse sequences provide information that is not available from absorption or fluorescence spectroscopies. 

Fluorescence Spectroscopy Studies of Intermolecular Interactions in Supercritical Fluids... 

Excimer fluorescence of pyrene attached to synthetic polymer chains can be used to study polymer conformation in solution and on particle surfaces. In this case, fluorescence spectroscopy involves the measurement of the emission intensity of monomer (/ , observed at 375 mn) and excimer (/ at 480 nm). The ratio of f to I is related to coiling/stretching behavior of a labeled polymer and we have called it the coiling index. In the absence of intermolecular interactions (the polymer concentration used is usually below this limit), a high value of IJI can be considered the result of a coiled conformation whereas a low value is associated with a stretched conformation. 

In normal Raman spectroscopy, the exciting frequency lies in the region where the compound has no electronic absorption band. In resonance Raman spectroscopy, the exciting frequency falls within the electronic band (Sec. 1.2). In the gaseous phase, this tends to cause resonance fluorescence since the rotational-vibrational levels are discrete. In the liquid and solid states, however, these levels are no longer discrete because of molecular collisions and/or intermolecular interactions. If such a broad vibronic bands is excited, it tends to give resonance Raman rather than resonance fluorescence spectra [101,102]. 

X HE CONFIGURATIONAL PROPERTIES OF WATER-SOLUBLE POLYMERS and their interactions with other polymers and with colloidal particles are relevant to understanding the intermolecular interactions in associative thickeners and steric stabilization of colloidal particles. We used fluorescence spectroscopy to study both the dynamic and the static equilibrium properties... 

Various tools may be used to probe intramolecular and intermolecular interactions and to study molecular packing in self-assembled fibers infrared or UV/Vis absorption spectroscopy fluorescence spectroscopy NMR spectroscopy X-ray diffraction and X-ray scattering etc. In this section we focus on the techniques that may provide information related to chirality. 

JF Brennecke, CA Eckert. Fluorescence spectroscopy studies of intermolecular interactions in supercritical fluids. ACS Symp Series 14 406, 1989. 

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