Poly electronic properties

Another possible modification of poly(sulfur nitride) that is expected to produce conducting polymers is the replacement of alternating sulfur in the thiazyl chain by an RC unit, i.e., [(R)CNSN]x. This type of polymer would have five r-electrons per four atoms in the repeating unit and, consequently, would have a partially occupied conducting band. The prospect of tuning the electronic properties of this polymer by... 

In this contribution, we discussed effects of disorder on the electronic properties of quasi-one-dimensional Peierls systems, like the conjugated polymer fraus-poly-acetylene. Since polymer materials generally are rather disordered and the effect of disorder on any quasi-one-dimensional system is strong, a proper description of these materials requires consideration of such effects. 

Structural and electronic properties of some poly molybdates reducible to molybdenum blues. R. I. Buckley and R. J. H. Clark, Coord. Chem. Rev., 1985, 65, 167 (104). 

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

An important challenge in the design of novel conjugated polymers is the synthesis of materials with tailor-made solid-state electronic properties. This section outlines the synthesis of the most significant classes of poly(para-phenylenevinylene)s (PPVs), poly(para-phenylene)s (PPPs), and related structures. Furthermore, this review demonstrates that the chromophoric and electronic properties of conjugated rr-systems are sensitive to their molecular and supra-molecular architecture. 

Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In principle, it should be possible to accomplish this experimentally under similar chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et al (16), including bandgap (1.17 eV) bandwidth (0.44 eV) ionization potential (4.2 eV) electron affinity (3.03 eV) oxidation potential (-0.20 vs SCE) reduction potential (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). 

The recent interest in substituted silane polymers has resulted in a number of theoretical (15-19) and spectroscopic (19-21) studies. Most of the theoretical studies have assumed an all-trans planar zig-zag backbone conformation for computational simplicity. However, early PES studies of a number of short chain silicon catenates strongly suggested that the electronic properties may also depend on the conformation of the silicon backbone (22). This was recently confirmed by spectroscopic studies of poly(di-n-hexylsilane) in the solid state (23-26). Complementary studies in solution have suggested that conformational changes in the polysilane backbone may also be responsible for the unusual thermochromic behavior of many derivatives (27,28). In order to avoid the additional complexities associated with this thermochromism and possible aggregation effects at low temperatures, we have limited this report to polymer solutions at room temperature. 

The use of organic polymers as conductors and semiconductors in the electronics industry has led to a huge research effort in poly(thiophenes), with a focus on the modification of their electronic properties so that they can behave as both hole and electron conductors. Casado and co-workers [60] have performed combined experimental and theoretical research using Raman spectroscopy on a variety of fluorinated molecules based on oligomers of thiophene, an example of one is shown in Figure 7. 

P.L. Burn, D.D.C. Bradley, R.H. Friend, D.A. Halliday, A.B. Holmes, R.W. Jackson, and A. Kraft, Precursor route chemistry and electronic properties of poly(p-phcnylcnc vinylene), poly[(2,5-dimethyl-p-phenylene)vinylene] and poly[(2,5-dimethoxy-p-phenylene)vinylene], J. Chem. Soc. Perkin Trans., 1 3225-3231, 1992. 

Most polymers do not form crystals suitable for single crystal X-ray diffraction, so powder or film methods are usually employed. X-ray and LJV data recorded at various temperatures provide the detailed information required to correlate conformational and electronic properties, since the former is sensitive to the inter- and intrachain packing, and the latter is sensitive to the conformation. DSC provides further evidence for any phase transitions. Detailed studies have been performed by Winokur and West,260 261 who reported a comparison of the polymorphism, structure, and chromism in poly(di- -octylsilylene), (Si- -Oct2), 89, and poly(di- -dccylsilylcnc)(Si- -Dcc2) , 90. These investigations will be described in detail for the useful insights into polysilane structures that they afford. 

Orchard B, Tripathy S (1986) Molecular-structure and electronic property modification of poly(diacetylenes). Macromolecules 19 1844—1850... 

CNTs can conjugate with nucleic acids via non-covalent bond. ssDNA, short double-stranded DNA and total RNA molecules can attach to the surface of CNTs and can disperse CNTs in aqueous environment. The poly(30T) has the highest dispersion efficiency (Zheng et al., 2003). For example, 1 mg DNA molecules mix with lmg CNTs in 1ml water, yield at most 4mg/ml CNT solution. DNA-CNT complexes can be purified or isolated by electronic properties such as agarose gel electrophoresis and centrifuge method (Cui et al., 2004a Karajanagi et al., 2004). 

In particular, poly(amidoamine) dendrimers were peripherally modified with diimide moieties (see the structure shown in Scheme 1.43). After rednction with dithionite, this dendrimer was cast into a film, the electronic properties of which were isotropic. (This means that on the molecular and macroscopic levels, there is a three-dimensional (3-D) electron delocalization.) The conductivity was humidity dependent. Water molecules integrate into the material s crystal structure and take part in long-distance electron transfer. Such an effect of water was also observed to enhance electric... 

The electronic properties of n-conjugated polymers reflect well the basic electron-withdrawing or electron-donating properties of the components of the Ti-conjugated polymer [62]. In view of the electrochemical reduction potential, the thiophene unit and tetrathiafulvalene unit (Nos. 8 and 9 in Table 1) have a similar electronic effect in PAEs. It is reported that poly(arylenevinylene)s are also susceptible to electrochemical reduction [63, 64]. Due to the electron-accepting properties, PAEs are usually inert in electrochemical and chemical (e.g.,by I2 [54]) oxidation. 

An important property of the alkyl poly silanes is their electronic absorption at relatively low energy. This was particularly surprising because such molecules lack tt, d ot lone pair electrons they were the first substances containing only bonding cr-electrons to show such long-wavelength absorptions. The unusual electronic properties of the polysilanes have sparked considerable interest in the chemophysical properties of these molecules. The UV spectra of cyclic polysUanes follow a quite different pattern . 

Research and development in the field are still continuing at a fast pace, particulady in the area of absorption and emission characteristics of the polymers. Several reasons account for this interest. First, the intractable poly dime thylsilane [30107-43-8] was found to be a precursor to the important ceramic, silicon carbide (86—89). Secondly, a number of soluble polysilanes were prepared, which allowed these polymers to be studied in detail (90—93). As a result of studies with soluble polymers it became clear that polysilanes are unusual in their backbone CT-conjugation, which leads to some very interesting electronic properties. 

Reynolds et al. have made an extensive study of electronic materials based on 3,4-propylenedioxythiophenes <2002CC2498, 2005AM422>. They now report that tethered poly(3,4-propylenedioxy)thiophene derivatives, for example, 42, provided a handle with which to tune the optical and electronic properties of the device <2006CC1604>. 

The Ir(III) trication is a 5d6 center and the electronic properties of its poly-imine complexes share several features with those of other well-known octahedral complexes of Fe(II) [14], Ru(II) [3], Os(II) [4], and Re(I) [5], whose metal centers are 3d6, 4d6, 5d6, and 5d6, respectively. Figure 3 depicts useful orbital and state energy diagrams for electronic transitions taking place in polyimine complexes of such d6 metal centers. 

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