Fluorescence Phenomena

Macromolecules may or may not fluoresce. Those that do are considered to contain intrinsic fluors. The common intrinsic fluors for proteins are tryptophan, tyrosine, and phenylalanine (the same three groups that absorb UV radiation). Macromolecules that have no intrinsic fluors can be made fluorescent by adding an extrinsic fluor to them. This is done by the process of chemical coupling or sample binding. The most common extrinsic fluors for proteins are l-aniline-8-naphthalene sulfonate, l-dimethylaminonaphthalene-5-sulfonate, dansyl chloride, 2-p-toluidyl-naphthalene-6-sulfonate, rhodamine, and fluorescein. The most common extrinsic fluor for nucleic acids are various acridienes (acridine orange, proflavin, acriflavin) and ethidium bromide. 

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The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

Sensitivity impacts upon the limit of detection and resolution of the device, making it a key performance parameter. Recently, several strategies have been developed in order to provide sensitivity enhancements for optical sensor platforms based on both optical absorption and fluorescence phenomena. These strategies are the result of rigorous theoretical analyses of the relevant systems and, combined with polymer processing technology and planar fabrication protocols, provide a viable route for the development of low-cost, efficient optical sensor platforms. 

Some rare-earth-activated materials do show strong fluorescence phenomena at temperatures even up to IOOO°C with a lifetime long enough to be detected without particular difficulties, as demonstrated in the cases of neodymium yttrium-aluminum-garnet(Nd YAG) andScPC>4 Eu3+ by Grattan etal.m and Bugos etal.,m respectively. 

R. K. Selli, Fibre optic temperature sensors using fluorescent phenomena, Ph.D. thesis, City... 

In recent years luminescence nomenclature has become confusing within the literature and in practice. Luminescence involves both phosphorescence and fluorescence phenomena. While luminescence is the appropriate term when the specific photochemical mechanism is unknown, fluorescence is far more prevalent in practice. Moreover, the acronym LIE has historically inferred laser -induced fluorescence however, in recent years it has evolved to the more general term light -induced fluorescence due to the various light sources found within laboratory and real-time instruments. Within this chapter fluorescence and LIE are interchangeable terms. 

Koch U, Fojtik A, Weller H, Henglein A (1985) Photochemistry of semiconductor colloids preparation of extremely small ZnO particles, fluorescence phenomena and size quantization effects. Chem Phys Lett 122 507-510... 

As mentioned at the beginning of this chapter, besides thermal energy to produce atoms, there are chemical methods for obtaining atomic or molecular vapors that are readily atomizable. The atoms generated from these vapors interact with electromagnetic radiation, and the resulting atomic absorption or fluorescence phenomena can be monitored or else they can be excited and their... 

This spatial inhomogeneity may also help explain observed fluorescence phenomena. Mandal et al. [143] reported evidence of a red edge effect (REE) [144] in the fluorescence spectra of chromophores solvated in a series of imidazolium-based ILs. In this phenomenon, the emission spectrum is observed... 

The three types of fluorescence phenomena described above are usually treated as separate phenomena. We shall show in this Review, however, that a unified approach can be given in which the sole parameter is the ratio of tire relaxation time of the excited molecule to the relaxation time... 

Figure 7.1 (A) Sdiematic representation of the Metal-Enhanced Fluorescence phenomena (B) FDTD calculations for two silver nanoparticle arrays...

Figure 7.1 (A) Schematic representation of the Metal-Enhanced Fluorescence phenomena (B) FDTD calculations for two silver nanoparticle arrays (d = 100 nm). (C) Wavelength-dependent calculated Ej maximum intensity for silver nanoparticle arrays (d = 100 nm). Geometries and incident field polarization [p-polarized) and propagation direction are shown in the insets. The gap between the nanopaiticles was assumed to be 2 nm in the calculations. (D) Calculated field enhancement as a function of distance for a single silver nanoparticle (d = 100 nm).The inset shows these results as an FDTD E image above the nanoparticle.

In the example just described, excited nitrogen dioxide is certainly a reaction intermediate, although perhaps not in the usual sense. However, if we are to admit to the scope of this discussion excited species which do not react further, then we should include also all fluorescence phenomena. Fluorescence studies do indeed... 

Visser, S. A. (1983b). Fluorescence phenomena of humic matter of aquatic origin and microbial cultures. In Aquatic and Terrestrial Humic Materials (R. F. Christman and E. T. Gjessing, eds.), Ann Arbor Science, Ann Arbor, MI, 183-202. 

In the case of polymeric dye assemblies, one observes several complex, ill-understood fluorescence phenomena. Very often it is observed that monomeric and dimeric aromatic dyes fluoresce strongly, whereas the fluorescence in large... 

Application of Raman spectroscopy to zeolite research was, for a long time, hampered by severe problems due to fluorescence phenomena. These could be overcome during the recent past (cf. Sect. 4.4 and [229]). Meanwhile, IR and Raman results of zeolite investigation, as reported in the literature are so muner-ous that an exhaustive overview would be beyond the frame of the present chapter [compare, therefore, also earlier reviews such as those by Yates [230], Ward [231], Baker et al. [232] (especially for Fourier transform far-infrared spectroscopy), Foerster [233] and Karge et al. [234]. However, in the following subsections many examples will be provided which are meant to demonstrate the high potential of IR, Raman spectroscopy and INS for the characterization of zeofites and related systems. 

The aim of this feature article is to outline our application of fluorescence techniques to polymer self-assembly smdies. We do not intend to give a complete survey of the use of fluorescence in polymer chemistry. We focus only on techniques that we have been using within the POLYAMPHI network. We start with a description of the principles of fluorescence phenomena and an explanation of the role of processes that influence the rates of transition and the spectroscopic characteristics. Then we discuss several examples of our experimental studies, in which we applied different variants of time-resolved measurements. Finally, we show how computer modeling can be used to support the interpretation of data on complex systems. 

Exciplexes are complexes of two different molecules usually of 1 1 stoichiometry. Their fluorescence phenomena are similar to those described for excimers, but their formation is not restricted to aromatic systems. If the sum of effective rate constants of the non radiative processes is so high such that the lifetime of emission is undetectable, these molecules do not necessarily luminesce. In contrast to the excimers, which are non polar, the exciplexes are polar entities. It was shown by Beens and co-workers [13] that exciplexes from aromatic hydrocarbons and aromatic tertiary amines demonstrate the charge-transfer character of the complexes as reported by Knibbe and co-workers [14], and their dipole moments were greater than 3.3 x 10 C m (10 D). 

Densitometric methods. In situ densitometry is an often-used technique for lipid quantitation and has been extensively reviewed by Prosek and Pukl (1996). Lipids are generally sprayed with reagent and their absorption or fluorescence can be measured under UV or visible light by means of a densitometer. The method needs to be standardized and suitable calibration curves need to be constructed to avoid errors. There are several models of densitometer available and some of them are highly automated and coupled to computer systems. Apart from these the use of CCD (charge-coupled device) cameras and colour printers have further improved the densitometric capabilities for accurate quantitations (Prosek and Pukl, 1996). A recent review by Ebel (1996) compares quantitative analysis in TLC with that in HPTLC, including factors that can effect quantitation, the need for careful calibration and errors in quantitative HPTLC analyses. Ebel is of the opinion that as both HPTLC and HPLC are based on the same absorption and fluorescence phenomena they should obtain similar results with respect to quantitation. 

Fig. 7 Chemical functionalities of the bioluminescence phenomenon (a), neutral and ionic forms of the firefly oxyluciferin molecule (b) and main differences of the chemiluminescence and fluorescence phenomena of a model coelenteramide based on mechanisms and geometrical...

Figure 2.14 Schematic description of the excitation and fluorescence phenomena.

Calcium, magnesium and aluminum compounds can be detected in qualitative filter papers by exposing the samples to oxine vapors fluorescent oxine compounds or complexes are formed. This test can be made at room temperatures if a piece of the paper is suspended over a crucible containing solid oxine. After a few minutes, a weak yellow-green fluorescence can be seen under an ultraviolet lamp and its intensity increases with longer exposure. If the vessel containing the oxine is warmed, the oxine (m.p. 79° C) volatilizes more rapidly and the fluorescence appears more quickly. The action of the oxine vapors cannot be satisfactorily explained by assuming that there is a transformation of the mineral constituents into the respective oxinates. A more probable explanation is that the oxine is chemically adsorbed (lake-formation ) and that this product exhibits the same fluorescence phenomena as those shown by the real inner complex metal oxinates. ... 

In the next section we show that, in the simplest cases, this scheme accounts for the observed relations between the concentration of the quenching solute and the intensity and lifetime of fluorescence. In subsequent sections we introduce additional processes, such as complex-formation or proton-transfer, in which the product may itself be a fluorophore, so that there are two excited states to be considered. This two-state model covers a variety of fluorescence phenomena. We discuss also the physical mechanisms of the various processes and the ways in which excited molecules lose their excitation energy. 

UV absorption and emission studies on SPS films have shown that fluorescence phenomena are essentially additive when the chromophore is simply absorbed in the polymeric amorphous phase or isolated guest of the clathrate co-crystal. On the other hand, the fluorescence of the intercalate SPS/TMB co-crystal, when excited at its absorbance maximum, is red-shifted with respect to both host and guest emissions (Fig. 10.5). This phenomenon has been attributed to a fluorescence bleaching, which is related to the three-dimensional order of the intercalate SPS/TMB co-crystals [147]. 

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