Conjugated Jt systems

It is well known that delocalized stable radicals may have potential for the construction of solid state conducting materials. The phenylalenyl radical 40 has been considered a good candidate with its spin density delocalized over 13 carbons in its jt-conjugated system. Unfortunately, 40 exists in equilibrium with its dimer and it decomposes at modest temperatures. To overcome the dimerization problem, Goto et al. and Koutentis et al. synthesized substituted radicals 41 and 42. 

Symmetrical Jt-conjugated systems showing inversion of the standard potentials... 

Gao et al. (2006) considered the data on an electron double resonance spectra of the cation-radical in conjunction with the results of calculation within the DFT. The authors established that the methyl group at the double bond of the cyclohexene ring is responsible for deprotonation of the P-carotene cation-radical. This route of proton elimination produces the most stable radical leaving the Jt-conjugation system to be intact. Deprotonation at the polyene methyl groups would... 

Tetrapyrroles contain an extended jt-conjugated system which is responsible for their use in a wide range of applications ranging from technical (pigments, catalysts, photoconductors) to medicinal (photodynamic therapy) uses. The electronic absorption spectra are governed by the aromatic 18 tt-electron system and typically consist of two main bands. In phthalocyanines the Q band around 660-680 nm is the most intense one accompanied by a weaker Soret band near 340 nm . In porphyrins the situation is reversed with an... 

Design of Jt-Conjugated Systems Using Organophosphorus Building Blocks... 

Chromophores based on aryl moieties can be easily grafted on to halophosphines via simple nucleophilic substitutions, as illustrated by the synthesis of 114 (Scheme 4.34). As a result, numerous phosphines bearing extended jt-conjugated substituents have been prepared. The aim of this section is not to give a comprehensive account of all derivatives that have been synthesized, but rather to illustrate how phosphorus fragments can be used either to influence or to organize the Jt-conjugated systems, with special emphasis upon fluorescence and NLO properties. 

This chapter addresses synthetic aspects of molecules with highly annelated chiral JT-conjugated systems, with the focus on helicene-type oligomers [20], In addition to synthesis, configurational stability (barriers for racemization) and selected chiroptical properties of such molecules will be discussed. 

Synthetic Approaches to Highly Annelated Chiral jt-Conjugated Systems S53... 

Organic materials with large optical rotations include cholesteric liquid crystals, molecules and polymers with chiral jt-conjugated systems, especially [n]helicenes [21, 31, 139]. The most important factor contributing to their large optical rotations is anomalous optical rotatory dispersion (ORD), which is associated with the presence of absorption (or reflection) with large rotational strength (Fig. 15.30). 

Another interesting application of Jt-conjugated systems is their use as chemosensors. For example, a modified dithienophosphole oxide 160 (see Scheme 49 for the synthesis of its precursor) that incorporates boryl-end caps is a very sensitive and selective sensory material for the fluoride ion (Scheme 126). Treatment of this derivative by fluoride induces a red shift of the emission maximum (160, 452 nm 373, 485 nm) that is visible to the naked eye. This shift in the fluorescence emission can even be detected down to micromolar concentrations of fluoride ion notably, the addition of other halides (CP, Br, P) does not affect the fluorescence in any way <20060L495>. 

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