Browsing by Author "Colpa, Johannes Pieter"

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Open Access
Investigation of the excited triplet states of [2.2]- and [3.3]paracyclophane
(1979) Melzer, Guenter; Schweitzer, Dieter; Hausser, Karl H.; Colpa, Johannes Pieter; Haenel, Matthias
We have studied the excited triplet states of [2-2]- and [3.3]paracyclophane by emission spectroscopy and by ODMR and have compared the results with the corresponding monomer paraxylene. The most striking result is that both phanes exhibit two sets of zero field splitting parameters indicating the existence of two nearly degenerate low lying excited triplet states. Furthermore, we find in distinction to expection a stronger reduction of the zero field splitting parameters as compared to the monomers for [3.3]paracyclophane than for [2.2]paracyclophane. The causes of these surprising experimental findings are discussed.
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 interactions in [2.2]phanes-relation between spectroscopic properties and structural parameters of [2.2]phanes
(1978) Colpa, Johannes Pieter; Hausser, Karl H.; Schweitzer, Dieter
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.