Interrupting conjugation

It is interesting that statistical copolymers 343, containing m-phenylene linkages that are supposed to interrupt conjugation, showed a PL maximum of 475 nm, similar to 342. Due to efficient energy transfer from the meta- to the para-linked chromophores, the emission maxima did not depend on the ratio of m- and p-divinylbenzenes, unless 100% loading of the meta units was used [420] (Scheme 2.54). 

Lipoxygenase (linoleate oxygen oxidoreductase) catalyzes the hydroperoxidation of fatty acids containing a methylene-interrupted conjugated diene system. The degradation of the hydroperoxides results in the formation of numerous secondary products (46-48). 

Figure 26-4 (A) Genetic map of E. coli, strain K-12 published in 1976. Data from Bachmann, Low, and Taylor.75 The scale in minutes is based on the results of interrupted conjugation experiments. The thr locus is arbitrarily taken as zero. The genetic symbols are defined in Table 26-1.

Incorporation of such dithienylethene units capable of reversibly interrupting conjugation into a polyene molecular wire permits reversible switching of conductive properties by photoirradiation.15 231 A typical example is shown below. 

It is clear that the most prominent feature of diarylethene switches is the potential to interrupt conjugation in a molecular type wire in which the switches are incorporated. In the open state, electronic interaction between the groups A (Scheme 11) at the periphery is blocked, whereas in the closed form electron delocalization is restored. 

Corphin (XII) is cross-conjugated at C-9 and upon diprotonation is transformed into the conjugated dication XIII. The remaining 7t-systems show interrupted conjugation at least at one peripheral position. 

As shown in Section IV,A,1, reduction of porphyrins by electron-transfer reactions may proceed via intermediates with interrupted conjugation, which subsequently rearrange to hydroporphyrins, thus reestablishing cyclic conjugation. Interruption of conjugation can also be achieved by catalytic hydrogenation of hydroporphyrins (Section IV,A,4). 

Oxidative attack at porphyrins usually occurs at meso positions to give meso-oxo derivatives of hydroporphyrins with interrupted conjugation. The field has been reviewed (81JA5854). Some oxidations, including oxidations of dications of porphyrins, attack the / -positions, yielding oxy or oxo derivatives of cyclic conjugated hydroporphyrins. Only transformations of this type are covered in this section. 

Note that such cis-dienic structures can be present only if intermolecular oligomerization of nitrile groups has taken place.) The Diels-Alder product interrupts conjugation, thus reducing color formation. In the particular case of maleic anhydride, and under the relatively rough conditions of stabilization, this type of reaction should lead to crosslinking, by cross-anhydridization ... 

The prefix homo (meaning one extra atom, interrupting conjugation, cf. homoaromaticity) has frequently been applied to sigmatropic rearrangements, but it is misleading. 

Albert, I.D.L., Marks, T.J., Ratner, M.A. Conformationally-induced geometric electron localization. Interrupted conjugation, very large hyperpolarizabilities, and sizable infrared absorption in simple twisted molecular chromophores. J. Am. Chem. Soc. 119, 3155-3156 (1997)... 

There are only two major classes of metals of primary importance in the above list—the porphyrin metals and the nonporphyrin metals. The porphyrin metals belonging to (aa) have been studied widely. The nonporphyrin metals have not yet been explored. The nonporphyrin metals could be (ab), (ac), and (ad) because in these categories the porphin skeleton has lost the physical properties of a typical porphyrin due to either interrupted conjugation or increased aromaticity. The more important types of nonporphyrin metals are those of the (b) category. In summary, the following definition is applied ... 

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