Poly electronic states

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

Table 2(a) Ground electronic states (GS) of oligomeric poly(phenoxyl) radicals. 

Figure 10 Density of electronic states plotted in the conduction band region of the poly(Gly-Ala-Ser) polymer (in relative units)...

Metal to metal charge transfer (MMCT) transition An electronic transition of a bi-or poly-nuclear metal complex that corresponds to excitation populating an electronic state in which considerable electron transfer between two metal centers has occurred. 

A few other techniques have been effectively used in the chemical study of OLEDs, including infrared spectroscopy [for the generation of carbonyl impurities in poly(p-phenylenevinylene)],20 photoemission spectroscopy (capable of measuring valence and core electronic states at the surface of the material during deposition),13,30,32 39 and gas chromatography (which is well suited for Alq3 because some of the reactants and products are volatile).16,35... 

The fluorescence of the phenyl polymer is similar in shape to the fluorescence from the alkyl polymers and the similar shape of the phosphorescence spectrum, as well, suggests that the origins of the electronic spectrum are also much the same. The apparent increased quantum yield for phosphorescence in poly(phenyl methyl silylene) probably reflects a mixing of the ring electronic levels with the levels of the chain. Both the fluorescence and phosphorescence of the naphthyl derivative are substantially altered relative to the phenyl polymer. Fluorescence resembles that of poly(B Vinyl naphthalene) (17,29) which is attributed to excimer emission. Phosphorescence is similar to naphthalene itself. These observations suggest that the replacement of an alkyl with phenyl moiety does not change the basic nature of the electronic state but may incorporate some ir character. Upon a naphthyl substitution both the fluorescence and phosphorescence become primarily tt-tt like. 

The results of an experimental study concerning the nature of the excited electronic states of poly(organosilylenes), a class of polymers in which the tackhone consists of covalently bonded silicon atoms, are presented. A comparison of the absorption spectra of dilute solutions of alkyl and phenyl substituted silicon backbone polymers at room... 

In order to proceed it is now necessary to consider the nature of the lowest excited state of these polymers. One description which appears to be particularly appropriate to these materials is that given by the molecular exciton theory (37,38). This of course is suggested by the nature of the fluorescence spectrum itself and in addition this approach has proven to be quite successful in the Interpretation of the electronic states of the alkanes, the structural analogs of the poly(organosllylenes) ( 3, 6). The basic assumption... 

The ESR susceptibility in PPy doped with polyanions, sulphated poly(/i-hydroxycthcr), sulphatcd poly(butadiene) and benzene sulphonate ions, as an example of disordered conducting polymers, was reported by Chauvet et al.. to show approximately a sum of the Curie and Pauli-like temperature dependence, but a small upturn above 200 K in some samples [293]. This behaviour is interpreted in temis of the thermal activation of the single bipolarons into their triplet state and such bipolarons are stabilized by bridging of adjacent chains through dopants [294], rather than of the usual intciprctation in tenns of the temperature dependent Pauli susceptibility [206]. The thermoelectric power of these systems shows small positive values, several pV, and square-root-like temperature dependence, typical for hopping systems with degenrate electronic states around the Fenni level [293]. 

At least in heavily doped polymers, the temperature-independent susceptibility is obsci-vcd in PT and P3AT (poly(3-alkylthiophenc)) doped with AsF(, [255,279, 282] PFc," [282] SO.iCF.r [295] CIO - [282,296] and BFj" [258], except for PT/P3AT-1T [255,297]. Possible reasons why it is not obseiwed in PT/P3AT-Ij arc (1) the ESR linewidth from the Pauli spins is too broad to observe by ESR and (2) the charge transfer from iodine to polymer is insufficient to fill a band gap. The situation with these systems is similar to the case of PPy on the metallic electronic states the electrical conductivity reaches 500 S/cm [298-300], the small... 

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