Dynamic nuclear polarisation in p-doped silicon by microwave ultrasonics

We have investigated the dynamic nuclear polarisation (DNP) of 29 Si nuclei in highly doped silicon single crystals. The saturation of the electronic Zeeman levels in a magnetic field of 3.3 kG at 1.6°K was obtained using microwave ultrasonics of about 9 GHz. The ultrasonic waves were generated in a cavity by means of a transducer consisting of a thin film of CdS evaporated on the polished surface of the silicon. Preliminary results obtained with a silicon-rod of 2 x 2 x 12 mm cut with the long axis parallel to the (110) direction rendered a reduction of the NMR signal to about ⅓ in agreement with the expected negative sign of the DNP

Transanular interaction in [2.2]phanes: [2.2](4,4')diphenylophane and [2.2](2,7) fluorenophane

The emission spectra and the zero field splitting parameters D and E of the first excited triplet states of [2.2](4,4′) diphenylophane 3 and of the two stereoisomeric syn- and anti [2.2] (2,7) fluorenophanes 4a and 4b are investigated and compared with those of the corresponding monomers

Transanular interactions in [2.2]phanes-relation between spectroscopic properties and structural parameters of [2.2]phanes

In this paper we attempt to explain the spectroscopic properties of a number of [2.2]phanes. All phanes discussed have in common that their two subunit

Influence of an identified dimer vibration on the emission spectrum of [2,2]paracyclophane

The emission spectrum of polycrystalline [2,2]paracylophane shows a resolved vibronic structure with a 241 cm−1 progression at He temperatures. The dependence of the energy of this mode upon selective deuteration in combination with results from FIR and Raman spectra could be used to identify the mode as a torsional dimer vibration. The emission spectra could be simulated assuming a linear coupling of the torsional mode to the electronic transitions with coupling strengths of S = 10 (fluorescence) and S = 13 (phosphorescence). This corresponds to an equilibrium displacement of the benzene rings under electronic excitation by a torsional angle of 10.6° (S1) and 12.1° (T1), in addition to the small torsion in the ground state S0 by about 3°

Electronic properties of two isomeric charge transfer [2.2]paracyclophanes

The emission spectra and the zero field splitting parameters of the two diastereomeric 4,7-dicyano-12,15-dimethoxy-[2.2] paracyclophanes 3 and 4 in comparison to the corresponding monomers 1 and 2 were investigated in order to study the orientation dependence of charge transfer (CT) interactions. The general results in glasses (PMMA) are: broad structureless emission bands with large spectral overlap between fluorescence and phosphorescence; strong reduction of the zero field splitting parameters D and D* by a factor of two for the pseudo-ortho isomer 3 and by a factor of four for the pseudo-geminal isomer 4 showing the strong effect of the geometrical orientation. In single crystals of the same phanes the zero field parameters were found to be further reduced to about one fifth of the value of the monomers which indicates, in accordance with the emission spectra, an additional intermolecular interaction between adjacent phanes

Transanular interaction in [2.2]phanes: models for dimers?

The emission spectra of pseudo-ortho 3 and pseudo-geminal-4,7,12,15-tetramethoxy[2.2]-paracyclophane 3 were measured in glass matrices at 1.3 K. Furthermore, the zero field splitting parameters D and E and the decay rate constants ki of the excited triplet state were studied by optical detection of magnetic resonance in zero field. The results were compared with the corresponding monomer 1,4-dimethyl-2,5-dimethoxybenzene

Spin rotation interaction and anisotropic chemical shift in 13CS2

The 13C nuclear spin-lattice relaxation time T1 was studied in liquid CS2 from -106°C to +35°C at resonance frequencies of 14, 30, and 62 MHz. The relaxation is caused by anisotropic chemical shift and spin-rotation interaction. It is shown that for linear molecules the spin-rotation constant C and the anisotropy of the chemical shift Δσ can be obtained from the relaxation rates without use of adjustable parameters. The analysis yields: C = -13.8 ± 1.4 kHz and Δσ = 438 ± 44 ppm

Spectroscopic properties of kekulene

Kekulene [1,2] is the first example of a new class of aromatic compounds in which the annelation of six membered rings leads to a cyclic system enclosing a cavity with hydrogen atoms

Electronic properties of kekulene

The fluorescence and phosphorescence of kekulene in a host matrix of polycrystalline tetrachlorobenzene are investigated, together with the triplet zero field splitting parameters |D| and |E| obtained by ODMR in zero field. The D value is also calculated within a semi-empirical π-theory and compared with experiment. It could be shown that the triplet state energies of a number of different sites of kekulene in the host matrix and the zero field splitting parameters are related, in first order, by spin orbit interaction