Chromophores molecular probes

Theories behind these methods were primarily developed for the determination of the absolute configurations of single molecules, especially steroids, and consist of derivatizing the molecule by substituting two identical chromophores at predetermined sites. Common substituents used as the molecular probes are para-substituted benzoates and polyacenes, e.g. 

Kmilarly, Sung et al. recently reported the use of azo chromophoric labels as a molecular probe of physical aging in amorphous polymers . By measuring the kinetics of trans cis photoisomerization of azo duomophores covalently bonded to amorphous polyurethanes, they defined a parameter a which corresponds to the fraction of the free volume above a critical size at a given temperature and time of aging. 

The water content in the medium plays a key role to control the colloid formation. The influence of the water content can be studied by using dynamic light scattering (DLS) and UV-vis spectroscopy. DLS indicates that when the water content increases above CWC, the hydrodynamic radius (i b) gradually increases as the water content increases. When the water content is above a certain value, i h starts to decrease as the water content further increases and then stabilizes at the final value. The structure evolution in the process can be better understood from the UV-vis spectroscopic investigation. It is well known that the photoisomerization rate and isomerization degree at the photostationary state are related to the free volume surrounding the azo chromophores (Kumar and Neckers, 1989). For azobenzene-type molecules, the isomerization behavior can be monitored by UV-vis spectroscopy and used as a molecular probe to detect the environmental variation in the systems. 

The application of fluorescence measurements to a large variety of chemical, biochemical, biological and physical problems is extensive. The majority of fluorescence applications involve the use of extrinsic fluorescence probes. These are chromophoric molecules that are attached to or adsorbed onto another molecule and their fluorescence is measured. These molecules probe the properties of the substances to which they are attached. The catalogue and manual published by Molecular Probes (9) is an excellent collection of a large number of different examples of the use of fluorescence, especially as they relate to bio-... 

Noncovalent interactions, such as hydrogen bonds, can qualitatively affect the electronic structure and properties of molecules embedded in molecular environments. Among such properties, electronic excitation energies are of particular interest because of the wide use of organic chromophores as probes in various environments [1 ]. Typically, hydrogen bonding results in shifts in the positions of absorption and emission bands anywhere between a few hundred and about 3,000 cm [5], This means that if one is to use computer modeling for interpretation of experimental data, the errors of the calculated shifts must be very small, on the order of 100 cm or less. 

This account has summarized several of our approaches to the preparation of electric-field-aligned chromophoric polymers for second order NLO applications. Molecular design has been employed wherever possible to arrive at structures that probe particular aspects of the polar orientation issue. The rich variety of accessible organic structures has enabled us to consider the orientation problem from a variety of points of view, and to indicate by example the manner in which multifunctional organic synthesis may play a role in the fabrication of oriented materials. 

Spectroscopic techniques, such as ultra-violet (9), Infrared (25), Nuclear Magnetic Resonance (24), and Fluorescence spectroscopies (5-8), constitute direct probes of specific events occurring at the molecular scale. When a quantitative interpretation is possible, spectroscopy provides very detailed microscopic information. Unfortunately however, the interpretation of spectra in terms of molecular events is often complex. Yet another approach that probes events at the molecular scale involves the use of tracers, such as chromophores (1-225). Again, the complexity of the tracer imposes limitations on the extent to which the data can be interpreted quantitatively. 

One of the challenges to the development of supercritical fluid (SCF) processes is understanding the solution thermodynamics on a molecular scale. Fluorescence spectroscopy has been shown to probe the local environment around chromophores. We now extend its use to SCF systems containing a cosolvent. 

Experimentally, these effects are tested by fluorescence and absorption measurements. These directly probe solvent polarization dynamics on molecular time-scales [100, 101]. For instance, the time resolved fluorescence spectrum of a chromophore, whose excited state dipole moment is subject to interactions with the surrounding solvent molecules, will exhibit fluorescence spectra that are strongly solvent dependent. The solvent molecules attempt to compensate the changes of charge density in the chromophore and, in sum, the fluorescence... 

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