Poly electron affinity

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

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). 

S. Janietz, D.D.C. Bradley, M. Grell, C. Giebeler, M. Inbasekaran, and E.P. Woo, Electrochemical determination of the ionization potential and electron affinity of poly(9,9-dioctylfluorene), Appl. Phys. Lett., 73 2453-2455, 1998. 

Bunz et al. pointed out that it would be of interest to develop materials that combine the stability, electron affinity, and high emissive quantum yield of PPEs with the excellent hole injection capabilities of poly(p-phenylene vinylene)s (PPVs) [48]. In line with this notion,recent synthetic activities have focused on the engineering of the band gap, conduction band, and valence band of PAEs with the objective to render these materials more useful for practical applications that exploit their electrically (semi)conducting nature. Examples of materials that emerged from these efforts are discussed in detail in other portions of this volume (in particular the chapters by Bunz, Klemm, and Yamamoto). They include, among others, poly(heteroarylene ethynylenes) such... 

Through reduction or oxidation of the molecule by a dopant molecule. Atoms or molecules with high electron affinity, such as iodine, antimony pentafluoride (SbCls), or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), may oxidize a typical organic semiconductor such as poly(p-phenylene) derivatives, leaving them positively charged. Reduction, i.e., addition of an electron, may be obtained by doping with alkali metals. 

The delocalization of the conduction electron onto the side chains would be expected if the pendant groups were replaced with more electrophilic substituents than the phenyl group. However, this is not the case. Figure 22 shows the absorption spectrum of poly-(methylnaphthylsilane) radical anion. The absorption spectrum is very similar to that of the naphthalene radical anion, which implies that the unpaired electron is localized on the pendant group. Increase of the electron affinity of pendant groups does not necessarily cause the delocalization. 

The Effects of Complexing Agents. Cai et al.66 replaced the sodium counterion of MX-DNA with various aliphatic amine cations, e.g. spermine cation, and alkyltrimethylammonium cation as well as polymeric amine cations, such as poly-L-lysine and polyethylenimine to vary the separation between DNA duplexes. The radiation-produced electrons from the complexing agents readily transfer to the more electron affinic DNA. 

Thermal polymerization of the VCZ-AN system was studied by Ellinger and it was reported that the homopolymer of poly VCZ alone was obtained (28). Due to the small electron affinity of weak acceptors such as AN and methyl methacrylate (MMA), total charge transfer from VCZ to acceptor was thought impossible this induced Ellinger to propose a new polymerization mechanism assuming mesomeric polarization between VCZ and acceptor to initiate and control the propagating step. The finding that AN did not copolymerize with VCZ seemed to support his mechanism. Later, spontaneous copolymerization of VCZ with MMA was reported by the same author. 

It seems to this writer that the first alternative is the correct one. A proton transfer from NHS to styrene- ion is unlikely to be faster than a proton transfer from NH3 to poly-styryl- ion, and it was shown that the latter reaction is not too rapid. Hence, if an electron transfer does take place one might expect dimerization of styrene ions and eventually initiation of polymerization. This might be an alternative explanation for the formation of a small amount of polymer during the reduction, but nevertheless this still remains to be only a minor reaction. On the other hand, in the reduction of 1,1-diphenyl ethylene, the electron affinity of which is higher than that of styrene, the dimeric di-ion, Ph2 C. CH2. CH 2. C. Ph2 is formed in comparable amounts with the monomeric Ph2 C. CH3ion (17). 

Poly- and oligothiophenes are generally p-type (hole-transporting) semiconductors. In thiophene-S,S-dioxide (98AM551 98JOC5497), this modification results in de-aromatization of the thiophene unit and increases the electron affinity and electron-transport properties of the... 

Several organics, e.g. pristine poly(3-octylthiophene), polyfluorene, bifunctional spiro compounds and polyphenyleneethynylene derivative, have been used for fabricating photOFETs. Responsivity as high as 0.5-1 A/W has been achieved in some of these transistors. We have already discussed the bulk heterojunction concept in Chapter 5. The bulk heterojunctions are fabricated using acceptor materials with high electron affinity (such as C<5o or soluble derivatives of C6o) mixed with conjugated polymers as electron donors. PhotOFETs based on conjugated polymer/fullerene blends are expected to show... 

For poly(9,9-di-n-octylfluorene) (PFO), which is deemed a model polymer in PFs, Janietz and coworkers reported its HOMO (equivalent to ionization potential, Ip) and LUMO (equivalent to electron affinity, Ea) levels as 5.8 and 2.12 eV below the vacuum level, respectively, as determined from cyclic voltammetry (CV) measurements of PFO thin solid film [11] as shown in Fig. la. However, the HOMO and LUMO levels provide a larger band gap of 3.68 eV than the value of 2.95 eV determined from the onset position in the ultraviolet-visible (UV) absorption spectrum of PFO film. If the band gap is taken as 2.95 eV and the HOMO level as 5.8 eV, the LUMO level of PFO... 

As shown in Table 1, the turn-on voltages for luminance at 0.01 cd/m were all between 2 and 5 V, strongly reduced as compared to the values reported for poly(alkylthiophenes)-based devices (Barta et al., 1998). This was the result of the increased electron affinity of compounds 1-6 induced by the S,S-dioxide functionalizaty and to the consequent reduction of the electron injection barrier. 

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