Electronic absorption poly

Fig. 18. Electronic absorption spectra of a poly(schiff base) obtained by polycondensation of 4,4 -diacetyldiphenyl sulfide and p-phenylenediamine (1) and of its complex with iodine (2)...

The electronic absorption spectra of dilute (typically 5-10 mg/1) solutions of poly(9,9-dialkyl-fluorenes) show a sharp peak with Amax 385-390 nm (3.2 eV) of tt-tt electronic transition. Thin solid films (spin coated from 15 to 20mg/ml solutions) reveal similar absorption with a slightly red-shifted ( 10 nm) and relatively broader peak (due to intermolecular interaction) (Figure 2.9) [246],... 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

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 . 

Figure 21 Comparison of the electronic absorption spectra of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical anions and cations at 77 K in -y-irradiated MTHF and freon matrices, respectively.

Figure 1. Variation of electronic absorption spectra of poly(2-vinylpyridine) MgBz initiated by dibenzylmagnesium as a function of time (a) 5 min (b) 70 h ...

Figure 4. Electronic absorption spectra of poly(2-vinylpyridine) MgBz initiated by benzylpicolylmagnesium in benzene.

As explained in the introduction, the polysilanes (and related polygermanes and poly-stannanes) are different from all other high polymers, in that they exhibit sigma-electron delocalization. This phenomenon leads to special physical properties strong electronic absorption, conductivity, photoconductivity, photosensitivity, and so on, which are crucial for many of the technological applications of polysilanes. Other polymers, such as polyacetylene and polythiophene, display electron delocalization, but in these materials the delocalization involves pi-electrons. 

Figure 2. The electronic absorption spectrum of poly(di n-hexylsilane). (a) solution in cyclohexane, (b) a solid film (1) recorded after baking to 100 C 1 minute (2) after standing for 10 minutes at room temperature.

Figure 3. The electronic absorption spectra of poly(di-p-n-hexylphenylsilane) ----solution in hexane,------solid film.

In this chapter, we report measurements on a diaryl-substituted polysilane, poly[bis(p-n-butyl)phenylsilane] (PBPNBPS), in which the bulky phenyl groups may provide more substantial steric hindrance to rotational freedom than do the dialkyl substituents. Reported values of the wavelength of maximum electronic absorption are large (395 10 nm) and cannot be attributed solely to electronic substituent effects (4). 

For essentially all n systems, electron transfer is connected with particular changes in the electronic absorption spectra. Thus, the usefulness of aromatic (poly)-anions and cations should particularly come to pass in cases when electron-transfer generated stages occur as short-lived mediators or as optoelectronic devices and sensors. 

Polysilanes are a unique class of polymers in which the o--electrons are delocalized entirely along the sp -bonded silicon backbone, causing their electronic absorption properties to be strongly dependent on the conformation of silicon backbones [2]. This property has created much interest in the structure of these polymers in the solid state [3]. In spite of the usefulness of solid-state NMR, there are few systematic studies on the Si CP/MAS NMR of polysilanes [4-6]. Most recently, it has been demonstrated that the VT Si CP/MAS NMR experiment is very useful to study the conformational features of polysilanes in the solid state [7j. Measurements of the Si CP/MAS NMR spectra of poly (methylphenylsilane) (PMPS), in the solid state over a wide range of temperatures, are performed and the conformation... 

Figure 8.9 Electronic absorption and fluorescence spectra of If measured at 20 l< in poly(vinyl butyral) film. The two emission curves correspond to excitation of different fractions of the ground state tautomeric forms.

Fig. 2. Formation of polybenz-imidazole 18 by FeCl3-catalyzed oxidative cyclodehydrogenation of poly-azomethine-type precursor polymer in dimethylacetamide at 60 °C, monitored by electronic absorption spectroscopy. Spectra were taken at time intervals over a period of 8 h. Curve 1(6) spectrum taken at start (on completion) of experiment...

Fullerene-styrene copolymers have been prepared in radical initiated and thermal polymerization reactions [148-151]. In radical copolymerizations of Cgg and styrene, copolymers with Cgg contents up to 50% (wt/wt) can be obtained [150]. Electronic absorption spectra of the copolymers are very different from that of monomeric C o (Fig. 36). The absorptivities per unit weight concentration of the copolymers j increase with increasing C q contents in the copolymers in a nearly linear relationship (Fig. 37). Fluorescence spectra of the Cgg-styrene copolymers, blue-shifted from the spectrum of monomeric Cgo, are dependent on excitation wavelengths in a systematic fashion [149]. Interestingly, the observed absorption and fluorescence spectral profiles of CgQ-styrene and Cyg-styrene copolymers are very similar, even though the spectra of monomeric CgQ and C70 are very different. The absorption and fluorescence spectra of the fullerene-styrene copolymers are also similar to those of the pendant Cgg-poly-styrene polymer (19) prepared in a Friedel-Crafts type reaction [150,156]. 

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