Chromophores poly

Keywords Acetylene chemistry. Cross-coupling reactions, Cyclo[n]carbons, Expanded radialenes. Molecular scaffolding. Nanostructures, Perethynylated chromophores, Poly(triacetylene), Tetraethynylethene. 

Fig. 6. Measurement of photostability of two polymeric electro-optic materials as carried out by researchers at IPITEK (TACAN) Corporation. The data represented by the solid line correspond to the LRD-3 DEC material of Dalton and co-workers [138] while the data represented by open circles correspond to a diaminonitrostilbene chromophore/poly(methyl methacrylate) guest/host material produced by IBM Almaden Laboratories. The dramatic improvement observed for the DEC material can be associated with increased lattice hardness from the chromophore coupling to adjacent polymer chains...

For the nonlinear optical response to be stable during processing and operation of chromophore/poly mer materials, the chromophores need to be chemically stable at all temperatures that the system encounters in electric field poling, and should withstand the fabrication steps needed for device fabrication. Usually, during device processing, the temperature can rise up to 250°C, whereas during operation, the material is subject to temperatures around 100°C for long periods of time. 

Electron-Deficient Polymers - Luminescent Transport Layers 16 Other Electron-Deficient PPV Derivatives 19 Electron-Deficient Aromatic Systems 19 Full Color Displays - The Search for Blue Emitters 21 Isolated Chromophores - Towards Blue Emission 21 Comb Polymers with Chromophores on the Side-Chain 22 Chiral PPV - Polarized Emission 23 Poly(thienylene vinylene)s —... 

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

The experimental results on poly(methacrylic acid) containing a small mole fraction of either 3-vinylperylene (PMAvPER, (30)) or lV-[12-(4-aminonaphthali-mide)]-2-methylacrylamide (PMAANI, (31)) show charge separation which is efficient for PMAvPER but not much for PMAANI. The quantum yields of charge separation for various chromophores covalently bound to PMA at pH 2.8 are summarized in Table 7. 

Table 7. Quantum yields of charge separation, (pcs, for poly(methacrylic acid)-bound chromophores at pH 2.8 [77]...

An important challenge in the design of novel conjugated polymers is the synthesis of materials with tailor-made solid-state electronic properties. This section outlines the synthesis of the most significant classes of poly(para-phenylenevinylene)s (PPVs), poly(para-phenylene)s (PPPs), and related structures. Furthermore, this review demonstrates that the chromophoric and electronic properties of conjugated rr-systems are sensitive to their molecular and supra-molecular architecture. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

Results are shown in Figure 5. Samples of PVCa were doped with 10% by weight of poly(1-vinylnaphthalene) to determine if the naphthalene chromophore would serve as a quencher for the surface oxidation of PVCa as it appears to do in the case of fluid solutions. 

Many of the linear conjugated tricyclic systems have interesting fluorescence or other electrophysical properties. Bis-pyrazolepyridines such as compound 30 have been incorporated into polymers as fluorescent chromophores <1999JMC339>, and used in doped polymer matrices <1997JMC2323>. They are electroluminescent at 425 nm and photoluminescent at 427 and 430 nm in a poly(vinylcarbazole) matrix with a quantum efficiency of 0.8. 

Since for the diarylpolysilanes, as for all polysilanes, the main chain is chromophoric due to the electronic transition between the delocalized silicon a and a orbitals, the electronic spectroscopies of CD, UV-Vis, and FL are particularly powerful probes of the structures of these materials. The magnitude of dimensionless quantity, gabs, is perhaps the most useful in comparing the CD spectra of optically active poly(diarylsilane)s. 

Photoluminescence (PL) in the polysilanes is well documented,34b,34c and for the poly(diarylsilane)s occurs typically with a small Stokes shift and almost mirror image profile of the UV absorption.59 This is due to the similarity of the chromophore and fluorophore structures in the ground and excited states, respectively, which is a result of the fact that little structural change occurs on excitation of the electrons from the a to the a orbitals. As PL is the emissive counterpart to UV, the emissive counterpart to CD is circularly polarized pho-toluminescence (CPPL). Where the fluorophore is chiral, then the photoexcited state can return to the ground state with emission of circularly polarized light, the direction of polarization of which depends on the relative intensities of the right-handed and left-handed emissions (/R and /l, respectively), which in turn depends on the chirality of the material, or more accurately, the chirality... 

The material system is a Langmuir-Blodgett film of the S enantiomer of a chiral polymer deposited on a glass substrate. The polymer is a poly(isocyanide)30 functionalized with a nonlinear optical chromophore (see Figure 9.14). In this particular system the optical nonlinearity and chirality are present on two different levels of the molecular structure. The chirality of the polymer is located in the helical backbone whereas the nonlinearity is present in the attached chromophores. Hence, this opens the possibility to optimize both properties independently. 

Figure 9.14 Chemical structure of 5-enantiomer of the chromophore-functionalized poly(isocyanide).

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