Browsing by Author "Staab, Heinz A."

Now showing 1 - 19 of 19

Open Access
1,8-dipyrenylnaphthalenes : syntheses, molecular structure, and spectroscopic properties
(1984) Wahl, Peter; Krieger, Claus; Schweitzer, Dieter; Staab, Heinz A.
Syntheses of the 1,8-dipyrenylnaphthalenes 1-3 are reported. The stereoisomers 1 and 2 were separated; their structural assignment is based on 1H NMR, on the optical activity of 2, and on X-ray structure analyses of 1 and 2. Kinetic parameters for the isomerisation 2 = 1 were determined by optical rotation measurements. - Emission spectra of 1 - 3 are discussed in comparison to monopyrenyl compounds 4 and 8. For 1 and 3 typical 'excimer-like' fluorescence is observed. The difference between 1 and 2 clearly demonstrates the dependence of excimer interactions between the pyrene units on the mutual orientation of the π-systems involved. - On the basis of X-ray analyses the molecular structures of 1- 3 are discussed with emphasis on π···π-interactions between the pyrene units.
Open Access
[2.2]- and [3.3]tetrathiafulvalenophanes
(1980) Ippen, Joachim; Chu, Tao-pen; Starker, Barbara; Schweitzer, Dieter; Staab, Heinz A.
In the "metallic" conducting 1:1 complex of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ), donor and acceptor molecules form separate stacks in the crystal. In order to enforce other TTF/TCNQ arrangements by altering the molecular architecture the phane-like bridged TTF-paracyclophanes (1), n = 3, and (2) were first synthesized. To do this a novel reaction sequence had to be developed which also facilitated synthesis of the tetrathiafulvalenophanes (3)/(4) (and the corresponding [2.2]-derivatives). (3)/(4) and TCNQ form a 1:4 complex having a conductivity of σ = 5 × 10−3 to 10−2 [Ω cm]−1 (single crystal, long axis, 300 K).
Open Access
[2.2]- und [3.3]Tetrathiafulvalenophane
(1980) Ippen, Joachim; Chu, Tao-pen; Starker, Barbara; Schweitzer, Dieter; Staab, Heinz A.
Um bei Charge-Transfer-Systemen, die als elektrische Halbleiter oder Leiter interessant sein könnten, durch Änderung der Molekularchitektur das Kristallgitter systematisch zu variieren, synthetisierten wir [2.2]- und [3.3]Tetrathiafulvalenophane ("TTF-Phane").
Open Access
[3.3]- and [4.4](2,7)pyrenophanes as excimer models : synthesis, molecular structure, and spectroscopic properties
(1984) Staab, Heinz A.; Riegler, Norbert; Diederich, Francois; Krieger, Claus; Schweitzer, Dieter
As excimer models the [3.3]- and [4.4]pyrenophanes 1 and 2 were synthesized. As the key precursor for the synthesis of 1 the octahydro-dithia[4.4]pyrenophane 9 was obtained by cyclisation of 4 and 8, the syntheses of which are described. Disulfone 10, derived from 9, on vapour-phase pyrolysis yielded 11 which by dehydrogenation was converted into 1. In an analogous route 2 was obtained via 16, 17, and 18 starting from 4 and 15 (prepared in the reaction sequence 12 - 13 - 14 - 15). - The molecular structures of 1 and 2, determined by X-ray structure analyses, are discussed with regard to transanular distances and deviations from planarity of the pyrene units. - Absorption spectra of 1 and 2 are discussed with reference to transanular interactions. The fluorescence emissions of 1 and 2 are found to be 'excimer-like'. Results obtained by ODMR measurements of 1 are reported.
Open Access
Electronic properties of [3.3]TTF-phan TCNQ-crystals
(1982) Schweitzer, Dieter; Taopen, Chu; Krieger, Claus; Staab, Heinz A.
-
Open Access
Electronic properties of kekulene
(1982) Schweitzer, Dieter; Hausser, Karl H.; Vogler, Helmut; Diederich, Francois; Staab, Heinz A.
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.
Open Access
Electronic properties of two isomeric charge transfer [2.2]paracyclophanes
(1976) Schweitzer, Dieter; Hausser, Karl H.; Taglieber, Volker; Staab, Heinz A.
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.
Open Access
Electronic spectra and triplet state properties of superphane
(1986) Schweitzer, Dieter; Hausser, Karl H.; Vogler, Helmut; Staab, Heinz A.; Boekelheide, Virgil
The emission and the zero-field splitting parameters D and E of the superphane 1 and the [25](1,2,3,4,5)-cyclophane 2 are investigated. The large number of six and five methylene bridges, respectively, leads to a more rigid molecular frame and to a smaller transanular distance as compared to other [2.2]cyclophanes. The experimental results exhibit characteristics features which are due to these unusual properties; they are discussed and compared with semi-empirical Π-electron calculations.
Open Access
Excited electronic states of flavin-containing coenzyme models
(1988) Gückel, Friedemann; Schweitzer, Dieter; Becker, Katja; Schirmer, Rolf Heiner; Zipplies, Matthias F.; Staab, Heinz A.
In order to gain further insight into the physical basis of flavin-catalyzed reactions, the interactions of a flavin with a second flavin and with other aromatic ring systems were studied. For this purpose compounds through 1 were synthesized These compounds contain the interacting units in defined geometric orientation. A monomeric flavin and glutathione reductase a flavoenzyme of known active-site chemistry, were included as reference molecules. The present report deals with excited triplet states of the flavin compounds as studied by optical spectroscopy and optically detected magnetic resonances (ODMR) at 1.3K.
Open Access
Molecular structure and spectroscopic properties of Kekulene
(1979) Krieger, Claus; Diederich, Francois; Schweitzer, Dieter; Staab, Heinz A.
Considerable bond localization has been detected in kekulene(1) by X-ray structure analysis: only every second ring is "aromatic". This initially surprising result is in accord with various spectroscopic properties of (1).
Open Access
Molecular structure and spectroscopic properties of kekulene (Cycloarenes, a new class of aromatic compounds ; 2)
(1983) Staab, Heinz A.; Diederich, Francois; Krieger, Claus; Schweitzer, Dieter
The molecular structure of kekulene (1) was determined by X-ray structure analysis. From the bond lengths of 1 a remarkable localisation of aromatic sextets and double bonds is concluded (cf. formula 1b). - The problem of annulenoid versus benzenoid diatropicity in 1 is discussed on the basis of 1 H NMR absorptions. These data, in agreement with recent theoretical calculations support a predominant ring-current induction in the benzenoid subunits of 1 and rule out a significant contribution of annulenoid structures like 1a. - Absorption and emission spectra of 1 are discussed as are the zero-field splitting parameters of the excited triplet state of 1.
Open Access
Molekülstruktur und spektroskopische Eigenschaften des Kekulens
(1979) Krieger, Claus; Diederich, Francois; Schweitzer, Dieter; Staab, Heinz A.
Beträchtliche Bindungslokalisation im Kekulen (1) wurde durch Röntgen-Strukturanalyse nachgewiesen: Nur jeder zweite Ring ist "aromatisch". Dieser zunächst überraschende Befund ist mit einigen spektroskopischen Eigenschaften von (1) in Einklang.
Open Access
ODMR of phanes and charge transfer phanes
(1979) Schweitzer, Dieter; Goldacker, Wilfried; Hausser, Karl H.; Staab, Heinz A.
Triplet zero field splitted parameters |D| and |E| and decay rates ki of the triplet sublevels of two stereoisomeric tetramethoxy [2.2] paracyclophanes as well as those of two CT [2.2] paracyclophanes in low concentration in glasses and small neat single ctystals as measured by ODMR in zero fields at 1,3 K are presented.
Open Access
Optical detection of magnetic resonance (ODMR) of triple-layered phanes
(1981) Melzer, Guenter; Schweitzer, Dieter; Hausser, Karl H.; Staab, Heinz A.; Zapf, Udo
-
Open Access
Spectroscopic properties of kekulene
(1981) Schweitzer, Dieter; Hausser, Karl H.; Diederich, Francois; Staab, Heinz A.; Vogler, Helmut
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.
Open Access
Transannular interactions in [2.2] phanes as studied by luminescence and optical detection of magnetic resonance
(1976) Schweitzer, Dieter; Colpa, Johannes Pieter; Hausser, Karl H.; Haenel, Matthias; Staab, Heinz A.
Emission spectra of different types of [2.2] naphthalenophanes were measured at 1.25 K in glasses as well as in small single crystals. In addition, the D and E values of the excited triplet states were studied by optical detection of magnetic resonance in zero field and the results compared with the corresponding monomeres.
Open Access
Transannular interactions in [2.2] phanes as studied by magnetic resonance and optical spectra
(1975) Schweitzer, Dieter; Colpa, Johannes Pieter; Behnke, J.; Hausser, Karl H.; Haenel, Matthias; Staab, Heinz A.
The interaction of π-electrons in [2.2] phanes was studied both experimentally and theoretically. The fluorescence and phosphorescence spectra were measured at liquid helium temperature; in addition, the zero field splitting parameters D and E were determined by ODMR in zero field and by ordinary ESR at X-band. The results for the phanes with two identical aromatic units can be summarized as follows: The rather small reduction of the D and E values of the order of 10% with respect to the monomers indicates, in agreement with the theoretical treatment given in part II, that the two unpaired electrons of the excited triplet state have a high probability to be at a given time in the same half of the molecule. While the fluorescence spectra show the typical behaviour of emission spectra of dimers or excimers, the phosphorescence spectra exhibit some remaining structure. This behaviour which indicates a somewhat weaker coupling among the triplet orbitals as compared to the singlet orbitals can also be understood on the basis of theoretical considerations. For a phane with two different aromatic units the behaviour is found to be more similar to the corresponding aromatic monomer with the lower excited states with some perturbation by the other part of the phase also in agreement with theoretical expectation.
Open Access
Transanular interaction in [2.2]phanes: [2.2](2,7)pyrenophane
(1976) Schweitzer, Dieter; Hausser, Karl H.; Kirrstetter, Reiner G. H.; Staab, Heinz A.
The emission spectra of [2.2](2,7)pyrenophane and the zero field splitting parameters D and E of its excited triplet state were measured in glasses and in small single crystals at 1.3 K. The results are being compared with monomer pyrene and 2,7 dimethylpyrene in liquid and solid solutions as well as in single crystals.
Open Access
Transanular interaction in [2.2]phanes: models for dimers?
(1979) Goldacker, Wilfried; Hausser, Karl H.; Schweitzer, Dieter; Staab, Heinz A.
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.