Donor-acceptor chromogens

The valence-bond approach may be used to provide a qualitative account of the /lmax values, and hence the hues, of many dyes, particularly those of the donor acceptor chromogen type. The use of this approach to rationalise differences in colour is illustrated in this section with reference to a series of dyes which may be envisaged as being derived from azobenzene, although in principle the method may be used to account for the colours of a much wider range of chemical classes of dye, including anthraquinones (see Chapter 4), polymethines and nitro dyes. 

Azo dyes of this type are classed as donor-acceptor chromogens and basically a red (bathochromic) shift is produced by the introduction of electron withdrawing substituents in the diazonium component and by electron donating substituents in the coupler. An interesting anomaly is the large bathochromic shift produced by am-acetamido group in the coupler (79JCS(P1)1990>. 

The vast majority of colored organic compounds are based on donor-acceptor chromogens, and with the exception of the polycyclic quinones and the phthalo-cyanines, all the commercially important synthetic dyes are of this type [34, 35]. 

Chromogenic development process, 1, 369-373 Chromogens donor-acceptor, 1, 329 Chromoglycic acid sodium salts... 

There is a third method proposed for classifying colorants which is in terms of the mechanism of the electronic excitation process. According to this method, organic colorants may be classified as donor acceptor, polyene, cyanine or n-rc chromogens. While this method of classification is undoubtedly of importance theoretically, it is arguably of lesser practical importance, since the vast majority of commercial organic dyes and... 

A new cross-conjugated methine-type chromogen was introduced in 1984. The dye Cl Disperse Red 356 (6.232) exemplifies this system, which contains two a,co-donor-acceptor dienone segments. The development of such benzodifuranone disperse dyes has been described [87]. 

Colour and Structure. The azo chromogen is one of the many that can be described as falling within the donor-acceptor group. The donor-acceptor system is shown in Figure 2.7 with a simple mono azo dye. Cl Disperse Red 1, to illustrate the point. The donor part of the molecule, as its name implies, contains donor groups such as amino and alkylamino, hydroxy and aUcoxy. Conversely, the acceptor part contains elec-non-acceptor groups such as nitto, cyano etc. These donor and acceptor groups may... 

Another example of Donor Acceptor type dye is Cl Solvent Yellow 44 (5). Here, the two carbonyl groups are acceptors, the naphthalene is the chromogen and the amino group at 4 position of naphthalene nucleus acts as the donor. 

Aegerter MA (1996) Sol-Gel Chromogenic Materials and Devices. 85 149-194 Ahrland S (1966) Factors Contributing to (b)-behavior in Acceptors. 1 207-220 Ahrland S (1968) Thermodynamics of Complex Formation between Hard and Soft Acceptors and Donors. 5 118-149... 

Khashaba et al. [34] suggested the use of sample spectrophotometric and spectrofluorimetric methods for the determination of miconazole and other antifungal drugs in different pharmaceutical formulations. The spectrophotometric method depend on the interaction between imidazole antifungal drugs as -electron donor with the pi-acceptor 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, in methanol or with p-chloranilic acid in acetonitrile. The produced chromogens obey Beer s law at Amax 460 and 520 nm in the concentration range 22.5-200 and 7.9-280 pg/mL for 2,3-dichloro-5,6-dicyano-l,4-benzoquinone and p-chloranilic acid, respectively. Spectrofluorimetric method is based on the measurement of the native fluorescence of ketoconazole at 375 nm with excitation at 288 nm and/or fluorescence intensity versus concentration is linear for ketoconazole at 49.7-800 ng/mL. The methods... 

---