Poly absorption maximum

The silyloxy-substituted precursor polymers (88) can be photocyclized in a polymer-analogous fashion to yield polymeric intermediates (90) containing the 3,6-phenanthrylene unit. These intermediates can be converted thermally to yield conjugated polyarylenevinylenes, in this case poly(3,6-phenanthrylene-vinylene) (91), a polymer that displays a long-wavelength absorption maximum at about 360 nm 1114]. 

Figure 4 Dependency of main-chain UV cr-a absorption maximum on chain length for poly(methylphenylsilylene) (PMPS) in toluene.18 Adapted with permission from Jones, R. G. Wong, W. K. C. Holder, S. J. Organometallics 1998, 17, 59-64. 1998 American Chemical Society.

By comparison of the UV, excitation, and PL spectral data with those of other poly(dialkylsilylene)s, a linear Si chain was inferred. Since poly(dipropylsilylene) is insoluble, the molecular weight could not be measured, but the UV absorption maximum at 345 nm is indicative of a DP of greater than at least 20 repeat units. The photo-CVD... 

Very interesting method of template polymerization was proposed by Japanese scientists. The method is based on the charge transfer interaction between template and monomer. In the course of the studies on the interaction of poly(maleic anhydride) with organic amines, the authors found strong charge transfer interaction of pyridines with poly(maleic anhydride). The polymer with pyridine gives brown-colored system with the absorption maximum at 480 nm. 

The steady state absorption and emission spectra of poly(A), poly(dA), and the absorption spectrum of the ribonucleotide monomer adenosine 5 -monophosphate (AMP) are shown in Fig. 1. The absorption spectra of poly(A) and poly(dA) are essentially identical. The AMP absorption spectrum is similar to the polymer spectra, but subtle differences exist. The absorption maximum of both homopolymers is shifted to the blue by several hundred wavenumbers, while the low energy band edge is red-shifted with respect to AMP. Similar shifts are observed at 77 K [15]. 

Helary and Fontanille 1781 have studied the influence of the tertiary amine crown molecule tetramethyltetraazocyclotetradecane (TMTA) upon the propagation of poly(styryl)lithium in cyclohexane at 20 °C using a rapid calorimetric procedure. The complexing agent, employed at a [TMTA] [Li] ratio of unity, caused a shift of the absorption maximum from 326 to 345 nm, indicating an increase in interionic separation it was presumed that, under these conditions, there is no aggregation... 

Whereas in solution the photoluminescence efficiency (Of) of poly(3-alkylthiophenes) (PATs) is 3(Mf)%, it drastically drops to 1-4% and lower in the solid state due to the increased contribution of nonradiative decay via interchain interactions and ISC caused by the heavy-atom effect of sulfur (97MM4608). Optoelectronic devices of this type of compounds have been studied (98SCI(280)1741 06SM(156)1241). Fibers of poly(3-hex-ylthiophene) for photovoltaic applications have been described (07MI1377). Poly(3-octylthiophene) showed a TTA band at 800 nm (96JPC15309). The photophysical properties of some alkyl and aryl polythiophenes have been studied (03JCP(118)1550). The absorption maximum of poly(3-octylthiophene) is at 438 nm, while the fluorescence was... 

Poly(3,3,-dimethyl-2,2 -bithiophene) shows an absorption maximum at 417 nm (90MM1268). Poly(3-phenylthiophene), on the contrary, showed absorption at 425-432 nm (91MM2694). Polythienothiophene and polydithienothiophene showed absorption maxima at 2.83 and 2.67 eV, while the fluorescence maxima were at 1.95 and 1.92 eV, respectively (87SM(18)177). 

The conjugation length of poly(3-alkylthiophene)s can be determined from the absorption maximum in the electronic spectrum. Whereas regioregular (i.e., head-tail) poy(3-octylthiophene) (POT) displays a maximum at 442 nm in CHCl3/Freon-113 solution, the absorbance maximum of 504 is blue shifted by 114 to 328 nm. This blue shift could arise from a particularly low molecular weight. 

When a thin film prepared from poly[(tetraethyldisilanylene)bis(2,5-thienylene)] was irradiated in air with a 6-W low pressure mercury lamp bearing a Vycor filter, the absorption maximum near 340 nm disappeared within 40 min. Poly[(tetraethyldisilanylene)(2,5-thienylene)] also exhibited a rapid UV change when its thin film was irradiated. IR spectra of the resulting films reveal strong absorption bands due to Si-O-H and Si-O-Si bonds at 3300 and 1100 cm [. The formation of the Si-O-H and Si-O-Si bonds can be best explained by the reaction of the silyl radicals generated by homolytic scission of the silicon-silicon bonds in the polymer backbone with oxygen in air. The other polymers are also photoactive,... 

Wurtz coupling of dibutylaminotrimethyl-l-2-dichlorodisilane forms a partially networked polymer.79 This networked polymer shows an absorption maximum at 360 nm, that is 30 nm red shifted relative to the absorption of poly (dialkylsilanes). The shift is due to the nonbonding electron pair of the amino substituents extending the a-conjugation of the silicon backbone. Two broad emission bands at 440 nm and 400 nm are observed and assigned to the network silicon units and the linear silicon chains, respectively. The unusual photophysical properties arise from both the amino side groups and the networked structure. 

Specific properties of polysilanes have been linked to the method of synthesis.35 For example, in the case of anionic polymerization of poly[l-(6-methoxy-hexyl)-l,2,3-trimethyldisilanylene] a new type of chromism was induced in the polysilane film by the difference in the surface properties of substrates and was termed a surface-mediated chromism. The polysilane exhibited thermochromism with an absorption maximum at 306 nm at 23°C, but <15°C a band at 328 nm began to appear. A monolayer of the polysilane was transferred onto both a clean hydrophilic quartz plate and a hydrophobic one treated with hexamethyldisilazane by the vertical dipping method. With the hydrophobic plate, a broad UV absorption at 306 nm is obtained, whereas the absorption on a hydrophilic plate shifts to 322 nm. The conformation of the polysilane is preserved by hydrogen bonding between the silica surface and the ether section of the substituent on the hydrophilic plate. The polysilane is attached to the hydrophobic surface only by van der Waals forces, and this weaker interaction would not sustain the thermodynamically unstable conformational state that is attained on the water surface. 

A representative example of indirect imaging with SWNTs labeled with fluorescent molecules was illuminated by Dai and coworkers.102 They solubilized as-produced SWNTs via sonication with fluorescein-modified poly (ethylene glycol) (Fluor-PEG, 114 PEG units). The absorption maximum of the nanotube-attached Fluor-PEG was red shifted 3 nm from that of free fluorescein, and the fluorescence intensity was quenched about 67% in phosphate buffer solution (pH 7.4). In the bioevaluation with BT474 breast cancer cells, substantial intracellular fluorescence was observed, suggesting cellular uptake of the Fluor-PEG-functionalized SWNTs.102... 

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