Vinylene shift

Vinylene shift Vinyl ester Vinyl ester resins... 

Because aH bonds within the polymethine chain of symmetrical PMDs are significantly equalized and change slightly on excitation, relatively smaH Stokes shifts (500 600 cm ) are observed in their spectra. In unsymmetrical PMDs, the essential bond alternation exists in the ground state. However, bond orders in the excited state are found to be insensitive to the symmetry perturbation. As a result, the deviations of fluorescence maxima, are much lower than those of absorption maxima, (3,10,56—58). The vinylene shifts of fluorescence maxima of unsymmetrical PMDs are practicaHy constant and equal to 100 nm (57). 

Calculation can also explain why in some thiazole dyes vinylene shift of the first two homologs is larger than the shift between higher members of the series, and also why wavelengths of absorption of nonsymmetrical dyes as calculated by the mean value rule differ from experimental data (6671. This deviation is caused by an interannular no-bond SS-interaction in the monomethine ion. 

Absorption characteristics, of hydrogenated amorphous silicon films, 22 133-134 Absorption coefficients, 23 126 Absorption-desorption towers, 10 614 Absorption maxima, vinylene shifts of,... 

Already before systematical investigations were started, it was anticipated that the known vinylene shift of 90—120 nm of the cyanine type may also be found in the violene type This situation has subsequently been expressed in a general theory of polymethines ... 

Quantitative MO-LCAO calculations as well as treatments as a one dimensional electron gas have been advanced. Special parameters, however, have to be introduced to account for different end groups and branching of the rr-system. Empirically a linear correlation between and n is verified in all cases so far investigated. That is, violenes behave like cyanines. The vinylene shift amounts to 100—150 nm in contrast to that of the corresponding forms OX and RED with 20-40 mm ... 

Horhold found that the action spectrum of phenyl-substituted polyarylene-vinylenes shifts substantially to longer wavelengths when the photoconductor probe is simultaneously irradiated by UV light from another source31. The action spectrum of photoconductivity of the polymer subjected to UV radiation is the same as the action spectrum of photoconductivity of the cation radical of the same polymer... 

Sulphur-containing polymethine dyes, including those incorporating thiazolidine and benzothiazole residues, exhibit certain anomalous chromophoric properties (e.g. abnormal vinylene shifts), which have been traced to an interannular non-bonded S-S interaction in the monomethine ion. The conclusion is supported both by a detailed examination of the... 

There have been very few examples of PTV derivatives substituted at the vinylene position. One example poly(2,5-thienylene-1,2-dimethoxy-ethenylene) 102 has been documented by Geise and co-workers and its synthesis is outlined in Scheme 1-32 [133]. Thiophene-2,5-dicarboxaldehyde 99 is polymerized using a benzoin condensation the polyacyloin precursor 100 was treated with base to obtain polydianion 101. Subsequent treatment with dimethyl sulfate affords 102, which is soluble in solvents such as chloroform, methanol, and DMF. The molar mass of the polymer obtained is rather low (M = 1010) and its band gap ( ,.=2.13 eV) is substantially blue-shifted relative to PTV itself. Despite the low effective conjugation, the material is reasonably conductive when doped with l2 (cr=0.4 S cm 1). 

The first set of dyes, so called visible set , is presented by polymethine dye PD 2630, squaraine dye SD 2243, and tetraone dye TD 2765, all with benzo[e]indolium terminal groups. The second set of dyes, so called NIR set , is presented by polymethine dye PD 2658, squaraine dye SD 2878, and tetraone dye TD 2824, all with 5-butyl-7,8-dihydrobenzo rJ furo[2,3-/]indolium terminal groups. A distinguishing feature seen from this figure is a remarkably large, 300 nm, red shift of the absorption bands for PD 2658 and SD 2878 as compared to PD 2630 and SD 2243. The absorption spectrum of TD 2824 is red-shifted by 200 nm as compared to TD 2765. Thus, the effect of the 5-butyl-7,8-dihydrobenzo[coT]furo[2, 3-/]indo-lium terminal groups is equivalent to the extension of the chain to three vinylene groups. 

Shim and coworkers [129] synthesized poly(2-fluoro-l,4-phenylene vinylene) 75 by the thermal conversion method. This polymer exhibits almost the same absorbance spectra as PPV 1 (Amax 410 nm), but the fluorescence band (Amax = 560 nm) is red-shifted by ca. 20 nm. The LUMO level was shifted down by ca. 0.15eV, facilitating electron injection but, in contrast to the above polymer 74, no fluorescence quenching was observed. Consequently, the PLED devices fabricated as ITO/75/A1 have about ten times higher EL efficiency than those fabricated with PPV 1 under identical conditions. 

Hanack and coworkers [161] reported related cyano-substituted naphthalene vinylene derivatives 126 and 127. Interestingly, replacing the phenylene unit in CN-PPV 113 with naphthalene in polymers 126 and 127 results in significant blue shift of the emission maxima from 710 to 595 nm (for 126a) and 500 nm (for 127). In addition, the efficiency, tested for double-layer device ITO/l/127/Mg Al(3 97), was rather low (3>el = 0.017%). 

Very recently, Liang et al. [198] reported the first poly(m-phenylene vinylene) homopolymer 168. Due to all-meta-linking of the phenylene units, the PL maxima (417 nm with a shoulder at 434 nm) of 168 is further shifted in the blue region and the emission band is very narrow, which promises to deliver a pure blue-emitting PLED (although a device fabrication was not yet reported). 

Lahti and coworkers [212] reported a series of meta-linked oligo(phenylene vinylene) block copolymers 181a-c. A mem-linked phenylene unit imposed an additional hypsochromic shift on the emission of these segmented polymers. The PL maxima were found at 399-416 nm, but a significant (ca. 70 nm) red shift was observed for EL spectra (ITO/polymer/Ca/Al) (Chart 2.39). 

A series of four fluorene-phenylene vinylene copolymers 320-323 clearly demonstrates the effect of the exact position of CN groups in the vinylene fragment on the emission of the materials (Scheme 2.48) [408], Substitution of benzene rings in copolymers 320 and 321 by thiophene results in red-shifted PL and EL, where copolymers 322 and 323 exhibit pure red emission with chromaticity values very close to the standard red (CIE x = 0.66, y = 0.34), although no PLQY values were reported. The ITO/PEDOT/322/Ca/Al device showed a very... 

A very remote secondary H/D isotope effect has been measured for the 2 + 2-cycloaddition of TCNE to 2,7-dimethylocta-2,fran -4,6-triene. The reaction of nitric oxide with iV-benzylidene-4-methoxyaniline to produce 4-methoxybenzenediazonium nitrate and benzaldehyde is thought to proceed via a 2 + 2-cycloaddition between nitric oxide and the imine double bond. A novel mechanism for the stepwise dimerization of the parent silaethylene to 1,3-disilacyclobutane involves a low-barrier [1,2]-sigmatropic shift. Density functional, correlated ab initio calculations, and frontier MO analysis support a concerted 2 + 2-pathway for the addition of SO3 to alkenes. " The enone cycloaddition reactions of dienones and quinones have been reviewed. The 2 + 2-photocycloadditions of homochiral 2(5H)-furanones to vinylene carbonate are highly diastereoisomeric. ... 

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