Poly quantum yield

Poly[2,5-dialkoxy-l,4-phenylene) vinylenejs with long solubilizing alkoxy chains dissolve in conventional organic solvents such as chloroform, toluene, or tetrahydrofuran [21, 28, 32-36]. Their emission and absorption spectra are red-shifted relative to PPV itself, and the polymers fluorescence and electroluminescence quantum yields are greater than parent PPV. This benefit may be a consequence of the long alkyl chains isolating the polymer chains from each other. 

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]...

Chiral dendrimers based on oligonaphthyl cores and Fr chet-type poly(aryl ether) dendrons have been investigated [44]. The absolute configuration of these dendrimers remains the same as that of their chiral cores. Both the nature of the core and the generation play a role in determining the fluorescence quantum yield. 

This result is further supported by the very short 130 + 10 ps lifetime combined with the remarkably high quantum yield of 0.43, both observed upon excitation at 335 nm, near the long-wavelength edge of the absorption band. These values combine to a radiative lifetime of 300 ps, which corresponds (33a) to an oscillator strength of 1.8. Similarly short emission lifetimes have been observed for other poly(di-n-alkylsilanes) di-n-pentyl, 200 ps, di-n-decyl, 150 ps. The average oscillator... 

Frequently B will also undergo a back hydrogen transfer which regenerates the parent ketone, as well as cyclization (in most cases a minor reaction) as a result of this competition the quantum yields of fragmentation are typically in the 0.1-0.5 range in non-polar media. When the Norrish Type II process takes place in a polymer it can result in the cleavage of the polymer backbone. Poly(phenyl vinyl ketone) has frequently been used as a model polymer in which this reaction is resonsible for its photodegradation, reaction 2. 

Kinetics with positive and negative amplitudes were observed for the natural ml-DNA and bm-DNA samples binding to 5.119 The kinetics were monitored by the fluorescence of 5 and the emission quantum yield for 5 bound to GC sites was much lower than for 5 bound to AT sites. The positive amplitudes were related to relocation of 5 from GC sites to AT sites. The different kinetics observed for ml-DNA compared with bm-DNA are in line with the observation that the binding dynamics of 5 with poly[d(G-C)] and poly[d(A-T)] were very different. 

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

Photochemical reactions of the pyrimidine polymers in solution were studied to determine the quantum yields of the intramolecular photodimerization of the pyrimidine units along the polymer chains. Photoreactions of the polymers were carried out in very dilute solutions to avoid an intermolecular(interchain) photodimerization. Quantum yields determined at 280 nm for the polymers (1-6 in Figure 1) are listed in Table I. The quantum yield of the 5-bromouracil polymer [poly(MAOU-5Br)] could not be determined because of side reactions of the base during the irradiation. 

Table I. Quantum Yields in Solution and Lithographic Evaluation of Poly methacrylates with Pendant Pyrimidine bases...

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

Bunz et al. pointed out that it would be of interest to develop materials that combine the stability, electron affinity, and high emissive quantum yield of PPEs with the excellent hole injection capabilities of poly(p-phenylene vinylene)s (PPVs) [48]. In line with this notion,recent synthetic activities have focused on the engineering of the band gap, conduction band, and valence band of PAEs with the objective to render these materials more useful for practical applications that exploit their electrically (semi)conducting nature. Examples of materials that emerged from these efforts are discussed in detail in other portions of this volume (in particular the chapters by Bunz, Klemm, and Yamamoto). They include, among others, poly(heteroarylene ethynylenes) such... 

The cross sections of dimer formation in poly T have been reported by Deering and Setlow,68 as functions of the wavelength, Figures 8 and 9. The corresponding quantum yields, from the ratios of adjSm where Sm is the absorption cross section, are shown in Table VII. 

Quantum Yields for Dimer Formation and Breakage in Poly T... 

The quantum yield for loss of absorbance in the photolysis of poly C (corrected approximately for change in hypochromoaticity) is about 7.5 x 10"3, and the thermal reversibility is about 85T,.7 The hypochromoaticity of poly C is high (about 40%). The thermal reversal rate as a function of temperature has been reported by Ono, Wilson, and Grossman82 1 (Fig. 34). 

This method of quantum yields calculation was verified in more detail in studying the photorearrangement of 4-methylphenyl benzoate (60) (in ethanol with 253.7 nm).71 The quantum yield of ester decrease, Additional examples are calculations of the photorearrangements of poly-4-benzoyloxystyrene (in dioxane with 253.7 nm) (cpA = 0.082, methyl-phenyl acrylate ([Pg.138]

For the initial phase of the photo-Fries rearrangement, IA can be determined approximately by subtracting the absorption due to the strongest absorbing product of the reaction mixture, provided its concentration and molar extinction coefficient are known. By means of this initial rate approach Humphrey8 determined the quantum yields of the photorearrangement of 13 (913-14 = 0.14), of 14 (914-.18 = 0.056), and of poly-2,2-propanebis(4-phenyl carbonate) ([Pg.138]

Table IV. Various Quantum Yields in the Irradiation of Poly (sty rene-co-vinyl aromatic ketone)s at 313 nm in N2...

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