Single molecule emission spectroscopy

One interesting new field in the area of optical spectroscopy is near-field scaiming optical microscopy, a teclmique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [, M]- Wlien applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a polymer film, illustrated in figure Bl.22,11 [82], Absorption and emission spectra of individual molecules can be obtamed with this teclmique as well, and time-dependent measurements can be used to follow the dynamics of surface processes. 

Optical properties of dendrimers bearing eight chromophores have been examined by single molecule spectroscopy techniques. It is especially exciting that variations in the spectra are recorded if one of these dendrimers is observed for a period of time under continuous irradiation.1481 The fluorescence intensity of the dendrimer nanoparticle also jumps between discrete emissive levels. All these findings suggest the existence of strong electronic interactions between several perylene imide chromophores within one dendrimer and provide new... 

The use of tunable lasers as sources in electronic absorption and emission spectroscopy has made possible a very considerable increase in resolution and precision. Electronic spectra are often difficult to analyze because of the many transitions involved. However, with a tunable laser source, one can tune the laser frequency to a specific absorption frequency of the molecule under study and thus populate a single excited electronic vibration-rotation energy level the resulting fluorescence emission spectrum is then simple, and easy to analyze. 

TNP-ATP complex obtained by the single-molecule time-resolved spectroscopy, together with a fluorescence decay curve of TNP-ATP obtained by a bulk measurement. Both curves were well fitted to biexponential functions. The instrument-response function in 195-ps fwhm is also displayed. (B) Representative fluorescence spectrums of two individual enzyme-TNP-ATP complexes showing different emission peaks. A fluorescence spectrum of TNP-ATP obtained from a bulk measurement is also displayed for comparison. All spectrums were normalized to unity at their maximum. (From Ref. 18.)... 

Reading the electronic state of the switch is often performed by use of optical transient absorption and fluorescence emission spectroscopy. Fluorescence is a much more sensitive technique, and can be done even at the single molecule level. 

The vertical ionization potential for a solvated chemical species can be the measure of its reactivity in the solution phase, especially for a single electron transfer reaction. It has been reported that the ionization potentials of anions in solution are conelated with the kinetic parameter for nucleophilic substitution reaction. This implies that an important aspect of the activation process of the reaction is a single electron transfer from anion to substrate. The ionization potential for solvated species has been available as the threshold energy E by photoeiectron emission spectroscopy for solution (PEES). This spectroscopic technique is able to provide the , values of almost any solvated species, such as organic, inorganic, cations, anions and neutral molecules in aqueous and nonaqueous solutions. 

The electronic state of the switch is often read by using optical transient absorption and fluorescence emission spectroscopies. Fluorescence is a much more sensitive technique, and can be used even at the single molecule level. It also requires a much smaller density of photons to provide a stable signal however, very few charge-separated ion pair states exhibit radiative charge recombination. In these cases transient absorption is often used because it allows direct nondestructive observation of a molecule s electronic configuration. Problems with this technique... 

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