Optical properties conjugated

The opportunity to synthesize new conjugated polymers with improved properties began to attract the attention of a larger number of synthetic chemists in the 1980s. Equally important was the subsequent development of stable, processible metallic polymers. As a result of these efforts, we now have a class of materials which exhibit a unique combination of properties the electronic and optical properties of metals and semiconductors in combination with the processing advantages and mechanical properties of polymers. 

Gas Phase to Solid State Evolution of the Electronic and Optical Properties of Conjugated Chains A Theoretical Investigation... 

Experiments on transport, injection, electroluminescence, and fluorescence probe the spatial correlation within the film, therefore we expect that their response will be sensitive to the self-affinity of the film. This approach, which we proved useful in the analysis of AFM data of conjugated molecular thin films grown in high vacuum, has never been applied to optical and electrical techniques on these systems and might be an interesting route to explore. We have started to assess the influence of different spatial correlations in thin films on the optical and the electro-optical properties, as it will be described in the next section. 

Additional chemical stability can be given to PPVs by substitution at the vinyl-ene carbons. Thus, CN-PPV and PPV-DP are more stable than their parent polymers [173]. Carter et al. [172] showed that a random copolymer of PPV containing non-conjugated segments is considerably more stable to photooxidation than the fully conjugated polymer. Of course, the electrical and optical properties are also altered by these substitutions. 

For copolymers of structure I, for both types of side-chains, there is a striking similarity with the optical properties of the corresponding models the absorption and photoluminescence maxima of the polymers arc only 0.08-0.09 eV red-shifted relative to those of the models, as shown in Figure 16-9 (left) for the octyloxy-substituted compounds. The small shift can be readily explained by the fact that in the copolymers the chromophorcs are actually substituted by silylene units, which have a weakly electron-donating character. The shifts between absorption and luminescence maxima are exactly the same for polymers and models and the width of the emission bands is almost identical. The quantum yields are only slightly reduced in the polymers. These results confirm that the active chro-mophores are the PPV-type blocks and that the silylene unit is an efficient re-conjugation interrupter. 

Uld aviolet spectroscopy and photoluminescence are used to study the optical properties of polymers. These spectra provide information about the conjugation along die polymer backbone and the photo behavior of die polymers. 

Poly(para-phenylenevinylene)s (PPVs) represent one of the most intensively investigated classes of rr-conjugated materials. Many synthetic procedures to generate unsubstituted and substituted PPVs have been developed. They include 1,6-polymerizations of 1,4-xylylene intermediates as well as several polycondensation methods. Parallel to the polymer syntheses, several series of PPV oligomers (OPVs) have been synthesized and characterized. Such model oligomers of different molecular size allow for a study of the dependence of electronic and optical properties on the length of the conjugated Ti-system. 

The discussion in this chapter is limited to cyanine-like NIR conjugated molecules, and further, is limited to discussing their two-photon absorption spectra with little emphasis on their excited state absorption properties. In principle, if the quantum mechanical states are known, the ultrafast nonlinear refraction may also be determined, but that is outside the scope of this chapter. The extent to which the results discussed here can be transferred to describe the nonlinear optical properties of other classes of molecules is debatable, but there are certain results that are clear. Designing molecules with large transition dipole moments that take advantage of intermediate state resonance and double resonance enhancements are definitely important approaches to obtain large two-photon absorption cross sections. 

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