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We present a triplet EPR study on photoexcitations in two different series of well defined thiophene oligomers. The first series consists of the so-called ‘end-capped' oligothiophenes with chain length n = 2−6. In the second series dodecyl chains are linked to α-oligothiophenes with n = 3, 6, and 8. Measurements of the triplet EPR spectra were performed using pulsed EPR spectroscopy. The characteristic lineshape of the EPR spectra provides evidence that photoexcitation leads to molecular triplet states in all compounds. We determined the fine structure parameters D and E and the population of the triplet eigenfunctions P x , P y , P z performing spectra simulations. The chain length dependence and the conformation dependence are discussed.

New alkaline earth metal endohedral fullerenes Sr@C 74 , Sr@C 76 -I,II and Ca@C 74 , prepared by means of the RF-method, have been isolated using multistep HPLC. The purity was ascertained by anionic LDI TOF mass spectroscopy, considering the isotopic patterns of the compounds. The influence of the incorporated metal on the electronic structure has been studied by VIS-NIR and Raman spectroscopy. Photoexcited triplet-state EPR spectroscopy was used to investigate the structure of these otherwise EPR-silent fullerenes. Displaying the frequency of the cage vs. en- Isolierung und spektroskopische Charakterisierung von neuen endohedralen Fullerenen im Größenbereich von C 74 bis C 76Inhaltsübersicht. Mit Hilfe eines Hochfrequenzofen wurden neue endohedrale Fullerene Sr@C 74 , Sr@C 76 -I,II und Ca@C 74 hergestellt und mittels mehrstufiger HPLC isoliert. Die Reinheitskontrolle erfolgte mittels Massenspektroskopie im anionischen Messmodus. Der Einfluss des eingeschlossenen Metalls auf die elektronische Struktur der Verbindung wurde mittels VIS-NIR und Raman Spektroskopie bestimmt. Die Struktur der an sich ESR-stillen

The EPR lineshape of the photoinduced triplet state of C60 in frozen toluene solution was studied by pulsed EPR spectroscopy. Lineshape calculations of the triplet spectra were performed including dynamical exchange effects. The observed spectra in a glassy matrix are compatible with zero field splitting parameters ‖D1‖ = 0.0114 cm−1 (12.2 mT) and ‖E1‖ = 0.0005 cm−1 (0.5 mT). The temperature dependence of the powder lineshape was simulated using a dynamical exchange model, where the triplet principal axis jumps between all equivalent sites allowed by the D5d symmetry for the lowest excited triplet state. The determined exchange rate turned out to be only weakly temperature dependent and suggests that the dynamic process is due to tunneling between Jahn–Teller distorted states rather than to real molecular jumps. In addition we have observed a different triplet state with zero field splitting parameters ‖D2‖ = 0.0100 cm−1 (10.6 mT), ‖E2‖ = 0.0015 cm−1 (1.6 mT) after annealing of the matrix. We attribute this to a C60 dimer or, alternatively, to crystal field effects.

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The new compounds [Ru(R-DAB)(acac) 2 ] (R-DAB = 1,4-diorganyl-1,4-diazabuta-1,3-diene; R = tert-butyl, 4-methoxyphenyl, 2,6-dimethylphenyl; acac -= 2,4-pentanedionate) exhibit intrachelate ring bond lengths 1.297 Ͻ d(CN) Ͻ 1.344 Å and 1.382 Ͻ d(CC) Ͻ 1.425 Å, which suggest a Ru III (R-DAB ·-) oxidation state formulation. This notion is confirmed by the negligible solvatochromism of the intense (ε ≈ 10 4 M -1 cm -1 ) charge-transfer absorption band in the visible region and by DFT calculations. Oxidation of the compounds occurs mainly at the R-DAB ·radical ligand to [a] 110 produce UV/Vis/NIR and electron paramagnetic resonance (EPR) spectroelectrochemically detectable Ru III species, whereas the reduction proceeds less reversibly and yields predominantly (R-DAB)-ligand-based spin for the 4-methoxyphenyl derivative, measured at low temperature. The results are discussed with respect to metal-to-ligand chargetransfer (MLCT) excited states of conventional (α-diimine)ruthenium(II) complexes and in view of other (α-diimine)metal complexes with ambiguous oxidation-state assignments.

The following pulsed electron nuclear double (ENDOR) and triple resonance schemes are discussed: Population transfer ENDOR, TRIPLE resonance, coherence transfer ENDOR, spin echo double resonance (SEDOR) and stimulated echo double resonance.