Spacers conjugated

III. Ferrocene Oligomers and Polymers with Conjugated Spacers... 

Effects of spacer groups on the formation and properties of the mixed-valence states of conjugated ferrocene dimers have been extensively studied by both electrochemical and spectroscopic methods. It should be noted that a characteristic feature in the electronic spectra of ferrocene dimers with conjugated spacer groups is the appearance of metal-to-ligand charge transfer (MLCT) bands in the neutral form as well as IT bands in the mixed-valence state. The dimer Fc — CH=CH — Fc... 

Proton-coupled intramolecular electron transfer has been investigated for the quinonoid compounds linked to the ferrocene moiety by a 7r-conjugated spacer, 72 (171) and 75 (172). The complex 72 undergoes 2e oxidation in methanol to afford 74, which consists of an unusual allene and a quinonoid structure, with the loss of two hydrogen atoms from 72 (Scheme 2). The addition of CF3SO3H to an acetonitrile solution of 74 results in two intense bands around 450 nm, characteristic of a semi-quinone radical, and a weak broad band at lOOOnm in the electronic... 

Another redox switchable system is based on dyad 21 in which 2-chloro-1,4-naphthoquinone is covalently attached to 5-dimethyl-aminonaphthalene via a non-conjugated spacer. The intrinsic fluorescence of the dansyl excited state in dyad 21 is strongly quenched, due to the intramolecular electron transfer from the excited dansyl to the adjacent quinone acceptor. However, the fluorescence can be switched on by addition of a reducing agent. Apart from chemical switching, the fluorescence of dyad 21 can also be switched electrochemically. This can be realized using a photoelec -trochemical cell, and the solution starts to fluoresce upon application of a reductive potential.31... 

A series of new D-71-A dendrimers (411-413) composed of four triphe-nylamine moieties as the donor groups share one benzothiadiazole chro-mophore in the middle as the acceptor, though various conjugated spacers... 

Density functional theory (DFT) calculations of two types of push-pull chromophores built around thiophene-based 7t-conjugating spacers rigidified by either covalent bonds or noncovalent intramolecular interactions (Figure 6) have been carried out to assign the relevant electronic and vibrational features and to derive useful information about the molecular structure of these NLO-phores <2003CEJ3670>. 

Phosphirene 93 <20060M5176> has been proposed as a useful and novel conjugating spacer within polythiophenes. Model studies on the monomeric unit 90 show that all the important criteria for that purpose (conjugation, stability) are fulfdled. 

Electron transfer across ferrocene-substituted oligo(phenylene-ethynylene)thiols (System 14) on gold has been studied using the ILIT technique [122] (see above) and electrochemistry [50]. Values of / = 0.57 + 0.02 and 0.36 A were obtained, respectively. Using the electrochemistry method, is 350 s for the 43 A, 36-bond, six-unit conjugated spacer, compared with 1.25 s for the 23 A, 18-bond alkanethiol... 

Since the synthetic reactions are intended to build the redox centers on one hand, and the conjugated spacer on the other, we have followed this order to present selected examples of syntheses. 

In this section, the reactivity of carbon- and heteroatom-containing substituents attached directly or indirectly to the heterocyclic ring of 1,3-dithiole derivatives is discussed. Here, chemical manipulations on these systems exclude ring carbon and sulfur atoms, which are the subject of Section 4.12.6. Special 1,3-dithioles called Jt-extended TTFs, containing two or more 1,3-dithiole moieties linked together via =C-(C=C) -C= or similar conjugated spacers, are discussed with typical TTFs in Section 4.12.11, although formally they constitute an example of functionalization of the 1,3-dithiole by 2rt-extended substituents, terminated by another 1,3-dithiole moiety. 

In this section, syntheses of 1,3-dithioles of a general formula 649 are discussed. This includes TTF structures 6, previously described in CHEC(1984) and CHEC-II(1996), and additionally new TTE-like structures containing two 1,3-dithiole heterocycles separated by Jt-conjugated spacer. Substituents and those in the spacer may contain... 

Structural modifications of the TTF system by insertion of conjugated spacer groups between the two 1,3-dithiole rings, or extension of the jr-system at the periphery of an intact TTF molecule, have been described [182], and some examples (LII-LIV) are shown. 

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