Broken conjugation

Gelinck GH, Warman JM (1996) Charge carrier dynamics in pulse-irradiated polyphenyle-nevinylenes effects of broken conjugation, temperature, and accumulated dose. J Phys Chem 100 20035... 

In addition to the mobility values which can be derived from the magnitude of transients such as those shown in Fig. 4, information can be obtained from the temporal form on the kinetics of the reaction of the polymer with the primary hole (or electron) and the rate constant for the ultimate charge recombination reaction which controls the decay of the conductivity at long times.Recent studies have looked into the influence of broken conjugation and polymer chain length on the intra-chain mobility. 

Candeias LP, Grozema FC, Padmanaban G, Ramakrishnan S, Siebbeles LDA, Warman JM. (2003) Positive charge carriers on isolated chains of MEH-PPV with broken conjugation Optical absorption and mobility. JPhys Chem B 107 1554-1558. 

Grage MML, Wood PW, Ruseckas A, Pullerits T, Mitchell W, Burn PL, Samuel IDW, Sundstrom V (2003) Conformational disorder and energy migration in MEH-PPV with partially broken conjugation. J Chem Phys 118(16) 7644-7650... 

The optoelectronic properties of dilute solutions of oligomeric and (broken-conjugation] polymeric PPV chains were studied using optical absorption and (time-resolved] emission spectrophotometry. The following properties were determined absorption and emission spectra, fluorescence quantum yields and decay times, exciton polarizabilities and dissociation probabilities, charge mobilities, and RC absorption spectra. The experimental results are compared with theoretical calculations of exciton polarizabilities, charge mobilities, and RC absorption spectra. ... 

The best way to understand how orbital symmetry affects pericyclic reactions is to look at some examples. Let s look first at a group of polyene rearrangements called electrocyclic reactions. An electrocyclic reaction is a pericyclic process that involves the cycli/ation of a conjugated polyene. One 7r bond is broken, the other 7t bonds change position, a new cr bond is formed, and a cyclic compound results. For example, a conjugated triene can be converted into a cyclohexa-diene, and a conjugated diene can be converted into a cyclobutene. 

Enterohepatic circulation can lead to toxic effects. For example, the drug chloramphenicol is metabolized to a conjugate that is excreted in bile by the rat. Once in the gut, the conjugate is broken down to release a phase 1 metabolite that undergoes further metabolism to yield toxic products. When these are reabsorbed, they can cause toxicity. The rabbit, by contrast, excretes chloramphenicol conjugates in urine, and there are no toxic effects at the dose rates in question. 

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