Fluorescent materials coumarins

Abstract Construction of chemical libraries is a useful approach to the discovery of better fluorescent materials, and several types, such as styryl dyes and cyanine dyes, have been reported. In this chapter, we focus on construction of a library of chemicals having a coumarin skeleton as the core structure. Coumarin and its derivatives are key structures in various bioactive or fluorescent molecules, and their fluorescence properties are dependent on the precise structure, including the positions of substituents. 

Many chemical compounds have been described in the Hterature as fluorescent, and since the 1950s intensive research has yielded many fluorescent compounds that provide a suitable whitening effect however, only a small number of these compounds have found practical uses. Collectively these materials are aromatic or heterocycHc compounds many of them contain condensed ring systems. An important feature of these compounds is the presence of an unintermpted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds ate derivatives of stilbene [588-59-0] or 4,4 -diaminostilbene biphenyl 5-membeted heterocycles such as triazoles, oxazoles, imidazoles, etc or 6-membeted heterocycles, eg, coumarins, naphthaUmide, t-triazine, etc. 

Another example of fluorescence intensity modulation in cou-marins is the 3-azido substitution that quenches the fluorescence completely. These compounds are used as starting material for the synthesis of fluorescent triazolocoumarins by click chemistry [31], Interestingly, the fluorescence of some coumarins depends strongly on the solvent. This is the case for 7-alkoxycoumarins that have been used as probes for microenvironments [32], 7-hydroxycoumarin that is pH sensitive, and 7-NR2 substituted coumarins such as coumarin 120 whose quantum yield is reduced in nonpolar solvents due to a change in the 3D structure [33],... 

Diethylamino-4-methylcoumarin is used to sensitize a weakly fluorescent second material in a mixture designed for use as an in situ flaw detector in metal surfaces. The energy absorbed by the coumarin is transferred to a second component with little energy loss by non-radiative processes. The blue fluorescence of the coumarin is replaced by the yellow-green of the other component, to which the eye is more sensitive. 

Organic dye materials represent the largest and best characterized class of probes used in all manner of fluorescent analysis. As an overall class, these dyes are used in almost all areas of biotechnology, including biosensing, cellular imaging, clinical immunofluorescence, and in DNA/protein microarrays (42-45). Several major structural classes of organic fluorophore span the UV-to-near-IR spectrum see Fig. 4. UV dyes are typically pyrene-based, naphthalene-based, and coumarin-based structures, whereas the Vis/near-IR dyes include a variety of... 

Some 60 dyes have been selected as possible photovoltaic materials their electrochemical redox potentials, surface adsorption, spectroscopic properties, fluorescence yields, and acid-base properties have been measured. The aim of this work is to produce a low-cost panel for harvesting solar energy as electrical power. The physical principles of fluorescent solar collectors have been discussed by Raue and Harnisch and several classes of dyes examined. Coumarin dyes are suitable convertors, particularly if the amino-group is fixed by ring closure to the aromatic system. 

In addition, they are widely used as fluorescent molecules for laser dyes,14 in the emission layer in organic light-emitting diodes,15 and as the fluorophore in fluorescent sensors.1617 Their fluorescence properties are known to depend upon the nature and position of substituents, and therefore several groups have constructed coumarin libraries to discover better coumarin-based materials. 

In addition to minimal perturbation of the original polymer structure, the polymer-fluorochrome bond must be stable and the labelled polymer should have favorable spectral properties. The highly fluorescent derivatives of fluorescein (la), rhodamine (Ila) and coumarin (Ilia) have been studied in detail for analytical purposes in biological material (Fig. 1). Attachment of these substances to a polymer molecule by a co-... 

A number of quinolone and pyridine materials function as metal ion probes. For example, a fluorescent probe that visualizes zinc in living cells was prepared from a carboxamidoquinoline (13T15). Diaryltrisphaeridines can be fluorescent detectors of copper ion (13T4631).A fluorescent probe uses dihydropyridine derivatives to respond to mercury ions (13T1617). Another zinc-sensitive probe was developed that contains two pyridines and a coumarin ring (13T4743). 

Fig. 1. A generalized scheme showing the kinds of secondary products that arise from the aromatic amino acids in higher plants. Several similarities are found in fungi and bacteria some fungi produce alkaloids ftom tryptophan and lignin-like materials from phenylalanine. Plant pathogenic fungi produce cinnamate and para and meta hydroxy phenyl-acetate from phenylalanine. Certain bacteria produce antibiotics and fluorescent pigments from metabolites in the shikimate pathway. Microorganisms are not known to produce coumarin, substituted coumarins, flavonoids and isoflavonoids.

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