Doping naphthalene

A number of attempts to transfer the spin polarization directly from the triplet electrons to the 13C spins that are present in the sample have been unsuccessful. Nevertheless, it is possible to polarize the 13C spins indirectly, by polarizing the 1H spins first, and then transporting the enhanced 1H polarization to the I3C spins by the conventional crosspolarization technique. Figure 18B shows the enhanced 13C spectra obtained in this way using the same crystal of pentacene-doped naphthalene. 

However, the recent experiments demonstrating (MI)ONP in polycrystalline samples were actually achieved by selective implementation of the ISE. In this work, an enhancement factor of 3160 was achieved in a poly crystalline (ground and pressed) sample of pentacene-doped naphthalene at 100 K in a field of 0.32 T (Fig. 8). However, instead of sweeping over the entire triplet ESR line (as is normally done with the ISE), the field sweep was designed to cover only a partial area of the ESR spectrum. With this approach (as implemented), only those crystallites with the long axis of the pentacene chromophores... 

Fig. 8. MIONP enhancement of nuclear spin polarization in a polycrystalline sample of pentacene doped naphthalene/ (a) Build-up curve for the enhanced spin polarization, with an MIONP repetition rate of 50 Hz (determined by the laser) the time constant for the build-up was 3730 s. TCP is an acronym for integrated cross-polarization - the authors term for their variant of the ISE. (b) 13.6 MHz single-shot H NMR spectra, taken with (top) and without bottom) MIONP enhancement (respectively, acquired at 100 K and room temperature). The top spectrum was obtained with a 10,000 s MIONP build-up time. The enormous sensitivity enhancement obtained with ONP is clear from comparing the two spectra. (Figures courtesy of K. Takeda and T. Terao, reprinted from Ref. [71], copyright 2001, with permission from Elsevier.)...

Time dependent fluorescence depolarization is influenced by the exciton annihilation which occurs in confined molecular domains . Photoemission results from singlet exciton fusion as shown by the excitation intensity dependence which occurs in anthracene crystals. Reabsorption of excitonic luminescence is an effect which has been shown to occur in pyrene crystals. The dynamics of exciton trapping in p-methylnaphthalene doped naphthalene crystals involves phonon assisted detrapping of electronic energy. Ps time resolved spectroscopy was the experimental technique used in this work. 

The UV and luminescence spectra of benzo[Z>]selenophene-doped naphthalene show that the properties of localized excitation states are different <83Ml 213-03). Charge transfer complexes of selenophene and some condensed derivatives were examined by UV, IR, and photoelectron spectroscopy and the experimental ionization potentials are in agreement with the calculated ones <82CS214>. 

Theoretical and experimental investigations into resonance hybridization between benzo[6-Jselenophene and naphthalene in benzoselenophene-doped naphthalene systems provided evidence for two nonequivalent centers for the impurity <85Mi 213-03). Chromatographic structural analysis by adsorption on graphitized thermal carbon black was used for the determination of conformation in 2-phenylchalcogenophenes <87MI 213-02). The adsorption of selenophene on various solid phases allowed its direct observation by EXAFS <9iMC6). 

Theoretical and experimental investigations into resonance hybridization between benzo[6]-selenophene and naphthalene in benzoselenophene-doped naphthalene systems provided evidence for two nonequivalent centers for the impurity. 

In non-doped anthracene crystals, as in non-doped naphthalene crystals at T = 300 K, two sharp Lorentzian ESR lines from excitons are observed (Figs. 7.18 and 7.21). They have, in complete analogy to the M lines of mini-excitons, a large and anisotropic fine structure (Fig. 7.19). The fine-structure constants of the triplet excitons in the anthracene crystal are D /he = -0.00575 cm and B /he = -1-0.0330 cm . The choice of axes is here the same as for the mini-excitons (cf. Fig. 7.11) z = b. From the measurements, the angle Z(x, a) = 27.25° is determined. VBth the methods treated in Sect. 7.4, this yields the fine-structure constants of the isolated anthracene molecule at room temperature, D/he = -1-0.0694 cm and E/hc = -0.00836 cm . (The small deviations from the values obtained for isolated anthracene molecules in a single-crystal matrix (see... 

Many expensive reductions such as the Birch reduction of naphthalene to isotetralin, benzene to cyclohexene, with metallic sodium and liquid ammonia, or reduction with LiAlHa, can generally be carried out electrochemically at much lower cost and under safe conditions. Electrochemical processes allow fluorinations to be carried out without using fluorine gas. Conducting polymers have been made by electrochemical processes which operate under ambient conditions, and the polymer can be synthesized, doped and shaped in film form in a single step. 

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. 

Several groups have studied naphthalene substituted anthracene derivatives as hosts or emitter materials in blue OLEDs (121, 202-205) (Scheme 3.63). The Kodak group used ADN as a host and TBP as a dopant in ITO/CuPc/NPD/ADN TBP/Alq3/Mg Ag [241]. They achieved a narrow vibronic emission centered at 465 nm with CIE (0.154, 0.232) and a luminescent efficiency as high as 3.5 cd/A. In comparison, the undoped device shows a broad and featureless bluish-green emission centered at 460 nm with CIE (0.197, 0.257) and an EL efficiency below 2.0 cd/A. The operational lifetimes of the doped device and the undoped device were 4000 and 2000 h at an initial luminance of 636 cd/m2 and 384 cd/m2, respectively. 

E. I. Newhouse and R. Kopelman, Fractal-like triplet-triplet annihilation kinetics in naphthalene-doped poly(methylmethacrylate), Chem. Phys. Lett. 143, 106-110(1988). 

Naphthalene was detected in soot generated from underventilated combustion of natural gas doped with toluene (3 mole %) (Tolocka and Miller, 1995). 

Both compounds crystallize with the cadmium diiodide structure (space group P3ml) as previously reported on polycrystalline samples.3 For platinum disulfide, ao = 3.542(1) A and c0 = 5.043(1) A, and for platinum ditelluride, a0 = 4.023(1) A and c0 = 5.220(3) A. Direct chemical analysis for the component elements was not carried out. Instead, precision density and unit-cell determinations were performed to characterize the samples. The densities of both compounds as determined by a hydrostatic technique with heptadecafluorodeca-hydro-l-(trifluoromethyl)naphthalene as the density fluid4 indicated that they are slightly deficient in platinum. For platinum disulfide, = 7.86 g/cm3 and Pmeas = 7.7(1) gm/cm3, and for platinum ditelluride, p = 10.2 gm/cm3 and Pmeas = 9.8(1) gm/cm3. In a typical experiment an emission spectrum of the platinum disulfide showed that phosphorus was present in less than 5 ppm. A mass spectroscopic examination of the platinum ditelluride revealed a small doping by sulfur (less than 0.4%) and traces of chlorine and phosphorus (less than 100 ppm). 

Among the dopes used may be cited the following combustibles colophony (used by Nobel in his Dynamites of 1869 1873) (Vol 3 of Encycl, p C403R) wood-meal, woodpulp and sawdust in Grisounite and in some Amer Dynamites cork,charcoal (in "Carbodynamite , described in Ref 60, p C52-L) naphthalene (in Rheinischdynamit) and cotton or other forms of cellulose (in "Forcites ). Less frequently have been used peat moss, ivoty nut meal, unbaked com flakes, starch, pulverised peanut hull, pulverized cottonseed hulls and sunflower seed shells... 

Phthalic anhydride is the most important product in the oxidation of o-xylene, which has become competitive with naphthalene as a feedstock for the industrial production of this component. This process is carried out at 350— 400°C and the industrial catalysts consist of doped V2Os or V2Os—Ti02 mixtures, pure or supported. Maximum yields of 70—75 mol. % (95—105 wt. %) are reported. Carbon oxides are the main by-products, besides minor amounts of tolualdehyde and maleic anhydride. Tolualde-hyde is the main product at low conversion and an essential intermediate in the phthalic anhydride formation, while maleic anhydride is mainly formed as a side-product directly from o-xlyene. 

Johnson and Willson interpreted the main feature of the observations on solid polyethylene doped with aromatic solutes in terms of an ionic mechanism it was analogous to that proposed for irradiated frozen glassy-alkane-systems in which ionization occurred with G = 3 — 4 [96], The produced charged species, electron and positive hole, were both mobile as indicated by the radiation-induced conductivity. The production of excited states of aromatic solutes was caused mainly by ion-electron neutralization. The ion-ion recombination was relatively slow but it might contribute to the delayed fluorescence observed. On the basis of Debye-Simoluchovski equation, they evaluated the diffusion coefficients of the radical anion of naphthalene and pyrene as approximately 4 x 10 12 and 1 x 10 12 m2 s 1 respectively the values were about three orders of magnitude less than those found in typical liquid systems. 

Many tests have been made of the validity of Forster-Dexter transfer in doped organic solids. A typical example is the classic solid solution study of anthracene and tetra-cene dissolved in naphthalene [26,166]. Energy originally absorbed by anthracene (donor) was shown to be transferred with high efficiency to tetracene (acceptor) by measuring the tetracene fluorescence. In these studies, the anthracene tetracene ratio was 1 1 and the mol fraction of the guests... 

Structural effects the free volume model. Demonstrative examples of the role of free spaces on Ps formation in solids are provided by solids in which no Ps is formed when pure, and where the Ps yield increases as some dopant impurity is added. This is the case for p-terphenyl, in which the Ps yield increases as either chrysene or anthracene are added. Both dopant molecules, when introduced in the p-terphenyl matrix, promote the formation of extrinsic defects having roughly the size of a naphthalene molecule [42], Similarly, doping the ionic KIO4 matrix by lOj ions induces the formation of oxygen vacancies which promote the formation of Ps [43],... 

---