Gabriela Claudia Frei

An Efficient and Facile Synthesis of Highly Substituted 2,6-Dicyanoanilines

A one-pot procedure for the synthesis of substituted 2,6-dicyanoanilines starting from readily available ynones and malononitrile has been developed. For instance, penta-1,4-diyn-3-one is converted into the acetylene-substituted aniline derivative 1 in good yield. Upon photoexcitation, this chromophore shows a strong blue emission with a high quantum yield. The ground- and the excited-state geometries, charge distributions, and excitation energies of 1 have been evaluated by ab initio calculations.

High-resolution laser spectroscopy of cyclometalated Rh (III)-thienylpyridine complexes

Abstract The cyclometalated rhodium(III) complexes [Rh(thpy)2L]+ with L=bpy, en or [μ-Cl2-(thpy)2Rh]− are studied in poly(methylmethacrylate) (PMMA) or in mixed crystals of the corresponding [Rh(phpy)2L]+ complexes. High-resolution luminescence and excitation spectra of the complexes at temperatures around 5 K are presented. The vibrational sidebands are fully resolved and allow us to compare the vibrational structure of the ground and lowest excited state. All thpy− complexes show nearly identical vibrational sidebands. The possibilities to obtain an estimate of excited state geometries are discussed.

Optically detected magnetic resonance spectroscopy of rhodium (III) mixed-chelate complexes

Abstract An optically detected magnetic resonance study of the lowest excited state of [Rh(thpy) (phpy) (bpy)] + , doped into a single crystal of [Rh(phpy) 2 (bpy)]PF 6 , is reported. Here, thpy − =2,2′-thienylpyridine, phpy − =2-phenylpyridine and bpy=2,2′-bi-pyridine. In emission, the dopant molecule gives rise to two zero-phonon lines, at 519.9 and 517.9 nm, respectively. The two zero-phonon lines are characteristic of the two structurally inequivalent forms of the dopant complex in the crystal lattice. From zero-and low-field ODMR data it is concluded that the lowest excited state in each of the two complex conformations is a phosphorescent triplet state. The fine structure splittings and the orientation of the fine structure tensor main axes of the triplet states of the two complex conformations are found to be different. It is argued that for both conformations the lowest excited state is a thpy − -localized 3ππ* state.

Excitation localization in mixed rhodium-chelates

Abstract Optically detected magnetic resonance experiments have been performed for photo-excited [Rh(thpy) 2 (bpy)] + doped in a single crystal of [Rh(phpy) 2 (bpy)]PF 6 . The results provide unambiguous evidence for a photo-induced triplet state excitation, localized on one of the thienylpyridyl anions chelated to Rh 3+ . The zero-field splitting parameters of the thienylpyridyl anion in the phosphorescent triplet state were determined to be | D | = 3445 MHz and | E | = 865 MHz.

Isolable zwitterionic pyridinio-semiquinone pi-radicals. Mild and efficient single-step access to stable radicals.

A rational design based on the proton-coupled electron transfer (PCET) concept allows us to structurally characterize for the first time isolable, air- and moisture-stable semiquinone radicals in a zwitterionic neutral form. The presence of an alkoxy and the bulky pyridinio substituents causes only a minor perturbation of either the redox potentials or the spectral UV-vis characteristics of the semiquinone core but significantly stabilizes the new radicals.