Conjugated chromophores structures

Determination of structural features. The ultraviolet spectrum has been of value in the determination of the structure of several vitamins. Thus the presence of an a-naphthoquinone system in vitamin K was first detected by this means. Also the 4-methylthiazole and the 2 5-dimethyl-6-aminopyridine system was first identified in vitamin Bj (thiamine), a- and /3-Ionones can be distinguished since the former contains two conjugated chromophores and the latter three conjugated chromophores. 

Fig. 8. Examples of some of the donor-acceptor substituted TEEs prepared for the exploration of structure-property relationships in the second- and third-order nonlinear optical effects of fully two-dimensionally-conjugated chromophores. For all compounds, the second hyperpolarizability y [10 esu], measured by third harmonic generation experiments in CHCI3 solution at a laser frequency of either A = 1.9 or 2.1 (second value if shown) pm is given in parentheses. n.o. not obtained...

The UV spectra of most of the triafulvenes hitherto known are rather complex in structure due to effects of either phenyl substitution or of conjugated chromophores at the exocyclic carbon, which obscure information on the cross-conjugated system itself. 

On the basis of the results discussed in section 3.1, concerning solvation effects on structure and electronic spectrum of chromophore Ml, we decided to carry out a corresponding study for merocyanines M2 and M3 (Fig.5) constituted by TT-conjugated chromophores of the same length , yet characterized by opposite solvatochromic behaviours. 

The structures of these compounds were established by spectral data. UV spectra of compounds 122-125 revealed of a phenolic system conjugated with a diosphenol moiety by the addition of base, AICI3 and AICI3-HCI which showed characteristic band shifts of this cross-conjugated chromophore. These results were identical with those reported for coleon U (126), lanugons R (127) and S (128) [72]. The spectral data of compounds 122-125 were given in Tables 19 and 20. The X-ray analyses of teuvincenones A (122) and C (124) confirmed their structures. 

The structure of (129) has been established by spectral data as well as by comparison with closely related compounds such as (16S)- and (16R)-plectrinone A (130,131). The UV spectrum showed characteristic band shifts of a cross conjugated chromophore by an a,P,Y,8-diunsaturated ketone moieties at 430 (sh), 370 (sh), 298, 254(sh) nm. The same group was found and studied on teuvincenones F and G (132,133) together with compound 129 from different collection of T. fruticans and on four... 

Figure 11.9 Flavoenzyme catalyzed electron transfer and oxidation/oxygenation reactions The extensive conjugation of the isoaUoxazine ring system results in the yellow chromophore ( ax = 450 nm) in the oxidized flavin. Flavin semiquinones are stable radicals, because the unpaired electron is highly delocalized through the conjugated isoaUoxazine structure. The neutral semiquinone is blue = 570 nm) and the flavosemiquinone anion is red (A ax = 480 nm). The...

In organic solvents, polyene antibiotics can be characterised by closely defined UV absorption maxima associated with the possession of a chromophore formed by the highly conjugated unsaturated structure of the molecule. Fully saturated... 

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