Other Chromophores

Quinophthalone Dyes. Currently, 3 -hydroxyquinophthalone [7576-65-0] is employed extensively in a number of product lines used to dye synthetic fibers in greenish yellow hues with good lightfastness and generally sufficient sublimation-fastness. Suitable substitution in the phthalic acid residue or the quinoline nucleus may improve thermosetting fastness [29], An example is C.I. Disperse Yellow54, 47020 [7576-65-0] (10)  

Methine Dyes. The condensation products of 4-dialkylaminobenzaldehydes with cyano acetic esters have long been used to dye acetate fibers. Brilliant greenish yellow dyes with excellent lightfastness are obtained on polyester fibers with the corresponding condensation products of malonodinitrile. The sublimation fastness of this dye type can be improved by introducing suitable substituents into the alkyl residue of the amino group or by doubling the molecular size, e.g., C.I. Disperse Yellow 99, [25857-05-0] (11) [12,30,31], 

Brilliant blue dyes such as C.I. Disperse Blue 354, 48480 [74239-96-6] (12) [32] are produced from aminobenzaldehydes and benzothiophene derivatives. 

Further condensation with malonodinitrile results in fluorescent red dyes such as (15). 

Oxidative cyanation of yellow 3-heteroaryl-4//-7-diethylaminocoumarin dyes such as 13 and 14 introduces a 4-cyano group and yields fluorescent red dyes [36], For example, treatment with NaCN followed by Br2 gives 16. 

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UV-VIS Unless the molecule has other chromophores alcohols are transparent above about 200 nm for methanol for example is 177 nm... 

The replacement of a benzene nucleus by a thiophene nucleus in compounds containing other chromophores causes more or less pronounced bathochromic shifts. These effects have been noticed in the thiophene analogs of malachite green (23), in cumulenes such as... 

Ultraviolet absorption spectra of tetrahy dro-1,3-oxazines do not show any maximum. Only after the introduction of a chromophoric group do bands appear. Thus 5-nitro derivatives show a strong maximum near 270 m/A, which is typical for a nitro group, and another one near 200 m(x which is probably also produced by the nitro group.In the instance of 5-nitro-5-hydroxymethyl derivatives, the absorption is much weakened this was explained by Urbanski in terms of a hydrogen bond between the hydroxyl and the nitro group. Other chromophores, such as C=0, C=NH, C—C, also cause the appearance of absorption maxima in the range 210-265 m/A and near 360... 

Wan s group showed that the observed photodehydration of hydroxybenzyl alcohols can be extended to several other chromophores as well, giving rise to many new types of quinone methides. For example, he has shown that a variety of biphenyl quinone methides can be photogenerated from the appropriate biaryl hydroxybenzyl alcohols.32,33 Isomeric biaryls 27-29 each have the benzylic moiety on the ring that does not contain the phenol, yet all were found to efficiently give rise to the corresponding quinone methides (30-32) (Eqs. [1.4—1.6]). Quinone methides 31 and 32 were detected via LFP and showed absorption maxima of 570 and 525 nm, respectively (in 100% water, Table 1.2). Quinone methide 30 was too short lived to be detected by LFP, but was implicated by formation of product 33 that would arise from electrocyclic ring closure of 30 (Eq. 1.4). 

The method described here can be applied to gain insight about environmental effects on the absorption and fluorescence of other chromophores and environments, including dyes used to probe the membrane potentials. 

Unsaturated groups, known as chromophores, are responsible for — tz, and k — 7t absorption mainly in the near UV and visible regions and are of most value for diagnostic purposes and for quantitative analysis. The mx and e values for some typical chromophores are given in Table 9.2. The positions and intensities of the absorption bands are sensitive to substituents close to the chromophore, to conjugation with other chromophores, and to solvent effects. Saturated groups containing heteroatoms which modify the absorption due to a chromophore are called auxochromes and include -OH, -Cl, -OR and -NRr... 

Inner filter effects due to the presence of other substances When the solution contains other chromophores that absorb light in the same wavelength range as the fluorescent compound under study, the chromophores act as filters at the excitation wavelength and the fluorescence intensity must be multiplied by a correction factor. If the chromophores do not interact with the fluorescent compound, the correction factor is simply the fraction of light absorbed by the compound at the chosen excitation wavelength, so that the corrected fluorescent intensity is given by ... 

An effort has also been made to determine the structure of products providing coloration in the Maillard reaction prior to melanoidin formation. The reaction between D-xylose and isopropylamine in dilute acetic acid produced 2-(2-furfurylidene)-4-hydroxy-5-methyl-3(2/f)-furanone (116). This highly chromophoric product can be produced by the combination of 2-furaldehyde and 4-hydroxy-5-methyl-3(2//)-furanone (111) in an aqueous solution containing isopropylammonium acetate. The reaction between o-xylose and glycine at pH 6, under reflux conditions, also pro-duces " 116. Other chromophoric analogs may be present, including 117,... 

Pyoverdin-like siderophores with other chromophores have also been observed (see Fig. 1) (45). The 5,6-dihydropyoverdins (Chra without the 5,6-double bond) and the ferribactins (Chrc) are considered to be biogenetic precursors of the pyoverdins 318) (the term ferribactin was originally used for the Fe " complex 221) and later for the free ligand). An azotobactin chromophore (Chrd, see also below Sect. 2.2) is occasionally found in Pseudomonas isolates e.g. 146)). Siderophores produced by a specific Pseudomonas strain but differing in the chromophore always have identical peptide chains. 

Other chromophores in this class are discussed under flnorescence in Chapter 3, e.g. coumarins (section 3.5.1.1), or under their use as pigments in section 2.4.1 of this chapter, e.g. perylene imides and derivatives (section 2.4.1.6). 

T tt transitions.14 These generally occur near 290, 180, and 160 mp, respectively. With more complicated carbonyl compounds, absorption of other chromophores is frequently superimposed on these regions, but the n -n transition is usually still observable. 

Several behaviors have been explored for encapsulated units that extend beyond those discussed here. These are mentioned briefly to indicate the wide variety of roles that dendritic encapsulation can play. Fluorescence quenching of an encapsulated chromophore can be attenuated by reducing the relative accessibility of dioxygen (a small molecule)1-7 or larger units such as other chromophore-encapsulated... 

The O-nitro group (the nitroxy group) gives an absorption band of about 270 va.fi, in the ultra-violet region, i.e. a band similar to that of the C-nitro group. A relatively small amount of work has been done on the ultra-violet absorption spectra of nitric acid esters but it has been established that in esters containing no other chromophoric groups absorption is extremely low (e = 10-20) even lower than in case of aliphatic nitro compounds. 

Several molecular properties can be measured using emission and excitation spectra. These include fluorescence lifetime, efficiency, anisotropy of the emitted light, mobility of chromophores, rates of quenching, and energy transfer to other chromophores. 

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