Emission conjugated chains

NHC6H4NH- unit this step can be reversed on treatment with N2H4 H20. The electrochemistry of [Ru(bpy)2(120)] + has been studied when the complex (in MeCN) is excited at 477 nm, the emission spectrum is almost completely quenched, and it is concluded that the rr-conjugated chains in (120) contribute to this effect. " ... 

By changing from a trans- to a m-con figured Pt(II) unit (i.e., from 21 to 75), the conjugation chain in 75 is disturbed (Xmax=364 nm for 75 versus 391 nm for 21), resulting in a much stronger triplet emission at room temperature (Fig. 9).32,33 However, the solubility of 75 notably decreases relative to 21, resulting in a lower molecular weight for the soluble fraction of the polymer. 

By suitable substituents, used at the same time to increase the yield and facilitate processibility. Substitution usually shifts emission toward the red (see Table 4). However, the absorption and emission spectra of phenylPPV (PPPV), in which the phenyl is substituted to one of the H atoms on the phenyl ring in the conjugated chain, is blue-shifted by several hundred angstroms [292]. 

The presence of oxidized thienyl groups in the conjugated chain of oligo- and polythiophenes deeply modifies their optical and photophysical properties with respect to their fully aromatic counterparts. Absorption and emission wavelengths are red shifted by several nanometers, owing to increased n-electron... 

In order to summarize this section it must be noted that the possibility to evaporate conjugated oligomers in such a way that their chain axes point predominantly in one direction allows us to determine the anisotropic electronic properties of conjugated molecules. From these studies it becomes evident that in order to obtain polarized absorption or emission of light as required in polarization Filters or LCD-backlights, the application of conjugated molecules is one of the most attractive areas of application for these materials. 

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. 

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