Conjugated polymers backbone

Lincar 1R absorption studies proved that there is no interaction between the conjugated- polymer backbone and the CWi molecule in the ground slate, as al-... 

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

Whether polymerized model membrane systems are too rigid for showing a phase transition strongly depends on the type of polymerizable lipid used for the preparation of the membrane. Especially in the case of diacetylenic lipids a loss of phase transi tion can be expected due to the formation of the rigid fully conjugated polymer backbone 20) (Scheme 1). This assumption is confirmed by DSC measurements with the diacetylenic sulfolipid (22). Figure 25 illustrates the phase transition behavior of (22) as a function of the polymerization time. The pure monomeric liposomes show a transition temperature of 53 °C, where they turn from the gel state into the liquid-crystalline state 24). During polymerization a decrease in phase transition enthalpy indicates a restricted mobility of the polymerized hydrocarbon core. Moreover, the phase transition eventually disappears after complete polymerization of the monomer 24). 

Conducting polymers based on polymer chains with conjugated double bonds are electroactive materials that have found widespread use also in the field of chemical sensors [11-41], Oxidation of the conjugated polymer backbone is accompanied by anion insertion or cation expulsion, as follows ... 

Conjugated polymers may be made by a variety of techniques, including cationic, anionic, radical chain growth, coordination polymerisation, step growth polymerisation or electrochemical polymerisation. Electrochemical polymerisation occurs by suitable monomers which are electrochemically oxidised to create an active monomeric and dimeric species which react to form a conjugated polymer backbone. The main problem with electrically conductive... 

Another class of photoinduced reactions known to produce large refractive-index changes is the polymerization of diacetylenes (29). These reactions are typically carried out in crystals of the monomer, and result in the production of a fully conjugated polymer backbone. Optical data on these materials are not very extensive, but from what information is available we estimate that nQ 10 22 cm3. (This is for light polarized parallel to the polymer backbone. For the perpendicular polarization the index change is about half as large.)... 

Upon exposure to heat, UV- or y-radiation diacetylenes are converted from a soluble monomer crystal which is transparent if pure, i.e., free of residual polymer, to a deeply colored polymer crystal. With a few exceptions, the latter is insoluble in all common solvents. The color arises from the lowest n-electron transition of the conjugated polymer backbone, which has its maximum near 600 nm. It is of excitonic origin 48-50) carries an oscillator strength of the order unity. Both insolubility and optical... 

FIGURE 5.2. pz orbitals along a conjugated polymer backbone. 

Compared to type I fluorescent polymers, the conjugated polymer backbone is the active chromophore. The monomer units that make up the polymer might not be inherently fluorescent. The absorption and emission of photons involve electronic transitions between a ground-state singlet (So) and a excited-state singlet (typically Si) as shown in Fig. 1.3. Radiative (kT) and nonradiative (km) transitions result in relaxation to the ground state and the observed kinetic lifetime t of these systems is governed by the relationship... 

---