Excited poly oligomers

The fluorescence excitation and emission spectra of the electrogenerated fused benzothiophene oligomers [poly(39) and poly(41)] show the existence of dramatic red shifts of the fluorescence maxima and important increases of the fluorescence intensity relative to the parent monomers. These results suggest the existence of extended electronic conjugation in the oligomer chains. Poly(39) and poly(41) showed a well-structured excitation band with maxima at about 335 nm and 395 nm, respectively. These excitation maxima are strongly red shifted by about 50 and 108 nm, respectively, against the 39 and 41 excitation spectra. The emission spectra are characterized by a relatively wide, poorly structured band, centered at 410 nm and 445 nm, respectively. These emission maxima also present dramatic red shifts relative to the emission spectra of the parent monomers. 

Fig. 16a-e. Changes of X-ray diffraction patterns upon heat treatment of as-polymerized poly-DSP crystals and photopoly-merization of DSP crystals, (a) As-polymerized poly-DSP, (b) heat-treated sample (1), (c) poly-DSP obtained after 50-min irradiation of the monomer with a xenon lamp, (d) heat-treated sample (2), and (e) DSP oligomer obtained by selective monomer excitation, (source Ref. 65)... 

It is of great interest that when the heat-treated sample (1) of poly-DSP in Fig. 16 is heated to 330°C (with the same scanning speed), the X-ray diffraction pattern of the resulting sample (2) changes into a pattern which is exactly the same as that of the as-polymerized oligomer crystals prepared by selective monomer excitation (see Sect. m.b.). 

Starting from the assumption that the geometry relaxation after excitation is of primary importance with respect to the luminescence response, we decided to employ a solid polymer matrix to suppress conformational changes of the oligomers. For the measurements, dilute blends with polysulfone as the transparent host matrix were prepared. In Figure 16-13, the PL decay curves for the two cyano compounds in both chloroform and polysulfone are presented, as are the PL spectra of Ooct-OPV5-CN in chloroform and poly sulfone [69]. 

Silicone Polymers - High energy UV irradiation of poly(phenylmethyl silane) results in end chain scission at the Si-Si bonds while alkoxypolysilanes show an increase in molecular weight. Two photon excitation of poly(dihex-ylsilylene) gives controlled oligomer formation containing ten Si atoms each. ... 

Regarding the nature of the excited states that are created when photons are absorbed, the experimental results are presented in Fig. 3.3. The figure shows absorption spectra in the Vis range, which were obtained for a series of oligomers of poly(p-phenylene vinyiene) (PPV). The four presented absorption bands all have a similarly fine structure and are shifted against each other the higher the number of monomers, the lower the frequency. A first conclusion can be drawn from the invariance of the profile of the bands. Since it is independent of the number of coupled monomers it must be a property of the monomer itself... 

A. Linear Optical Excitations of Poly(p-phenylene vinylene) Oligomers... 

In this section, we examine the electronic excitations of poly(p-phenylene vinylene) (PPV) oligomers (Figure 3A) and their scaling with molecular size. Understanding the electronic structure and the overall electronic excitation processes in this photolumi-nescent polymer is needed to provide a consistent picture for the numerous experimental and theoretical studies of PPV. 

The Raman spectra of doped states of polyaniline [99], poly(/ -phenylenevinylene) [75, 100-102], and polythiophene [72, 73] have been also analyzed on the basis of the data of charged oligomers (charged oligomer approach). The detected self-localized excitations are summarized in Table 4-5. Some important conclusions can be drawn from these Raman studies. 

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