Fluorescence polysilane

Absorption and Emission Spectra. The excitation-emission spectrum of 1 (bottom half of Fig. 1) shows that the relatively narrow emission band is nearly independent of the excitation wavelength and that the excitation spectrum is not only nearly independent of the wavelength at which the emission is monitored, but is also very similar to the absorption spectrum, both being somewhat broader than the emission band. This leaves no doubt that the observed emission is due to the polysilane, and its shape, location and the mirror image relation to the absorption permit its assignment as fluorescence. 

Since only polymers obtained from the cyclic starting materials 5, 6, 7, 10, 11 and 12, which are likely to have siloxene-like structures, exhibit color and fluorescence, the polysilane ring seems to be essential for the exceptional optical properties of siloxene. This is in agreement with the original idea of Kautsky, who assumed the cycle to be the chromophore. 

The polysilanes are characterized by strong two-photon absorptions which lead to the production of a strong induced birefringence (An — 0.03 632.8 nm) caused by anisotropic photodestruction. The spectral response of the two-photon induced birefringence identical to that determined by two-photon fluorescence excitation. In each case a strong resonance occurs around 570 nm ( 4.28 eV... 

The fluorescence of polysilanes has received much attention in recent years, in part because of the discovery that some poly silanes are electroluminescent, and so may have applications in display technology. Fluorescence spectra, quantum yields, lifetimes and other properties for dialkylpolysilanes have been thoroughly investigated by Sun and coworkers.98 Dialkylpolysilanes exhibit fluorescence of a rather normal type, in which the emission is a mirror image of the absorption, with a rather small Stokes shift. This suggests that the emission takes place from a highly delocalized state, probably an... 

The branched polysilanes show a broad emission peak around 450 nm, where the large red shift in the fluorescence spectra is due to the influence of aryl substituents and the introduction of branched points. For (opto)electronic applications, the UV irradiation and thermal stability are crucial to device stability. Branched polysilanes have better thermostability and are more resistant to UV irradiation than are linear polysilanes. 

Polysilane-based nanostructured composites were synthesized by the inclusion of poly(di-w-hexylsilane) (Mw = 53,600) into mesoporous, Si-OH-rich silica with a pore size of 2.8 nm.81 Two PL bands are observed for the composite. A narrow band at 371 nm, assigned to a PDHS film on a quartz substrate is blue shifted by 20 nm, a shift attributed to the polymer being incorporated into the pores.82 The size of the monomeric unit of the PDHS is about 1.6 nm, so only one polymer chain can be incorporated into a mesopore with a diameter of 2.8 nm. The narrow PL band at 350 nm is due to the reduction of the intermolecular interactions between polymer chains. This narrow PL band at 350 nm is assigned to the excited state of the linear polymer chain.81 Also, a new broad band of visible fluorescence at 410 nm appeared, which is assigned to localized states induced by conformational changes of the polymer chains caused by its interaction with the silanol (Si-OH) covered pore surface. Visible luminescence in nanosize PDHS is observed only when the polymer was incorporated in hexagonal pores of 2.8 nm and is not seen for the polymer incorporated into cubic pores of 2.8 nm diameter or hexagonal pores of 5.8 nm diameter. 

It is perhaps relevant here that the fluorescent compound formed in the hydrolysis of iodine cyclosilanes also has rings isolated by oxygen. It is significant, moreover, that two-dimensional polysilanes become fluorescent if a slight partial oxidation takes place. 

The polysilanes generally exhibit intense, short-hved fluorescence. Competing with the fluorescence are photochemical reactions, of which three are most important. At high photon... 

The various photoprocesses are important for several potential applications of polysilanes. Because of their intense fluorescence they have been suggested as scintillation materials for radiation detection. The chain-breaking reactions mean that polysilanes can be degraded by UV light it is this property that makes them useful as photoresist materials. 

Excited state dynamics have been measured in polysilane by ultrafast techniques and site selective fluorescence studies made with polysilylenes. ... 

Key words TNT, explosives, sUole, germole, polysilane, pofygermole, polysilole, sensors, luminescence, fluorescence, nitroaromatics, quenching, inorganic polymers... 

Polysilanes are air-stable Si-Si backbone polymers that exhibit efficient emission in the UV spectral region, high hole mobility, and high nonlinear optical susceptibility [28]. These properties arise from delocalization of a electrons along the Si-Si chain. Polysilanes have been employed as fluorescent materials for radiation detection, as electroluminescent materials for display devices, and as photorelractive materials for holographic data storage [28]. 

Fluorescence spectroscopy in combination with circular dichroism (CD), optical rotatory dispersion. X-ray crystallography, UV and NMR spectroscopy of the main chain is a powerful probe for identifying helical conformation, uniformity, and rigidity in polymers. In recent years, these techniques have been applied extensively to investigate the structures of polysilanes in both the solid state and in solution and it is now clear that after electronic structure main chain helicity is the principal determinant of the properties of polysilanes. In... 

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