Roland Paetzold

Thermochromism and photochromism of aryl substituted acyclic azines1: Uncatalised and acid-catalised thermal isomerisation

Abstract The photochemical E-Z isomerisation of the benzophenone-9-anthraldehyde azine (1), benzophenone-9-acridine aldehyde azine (2) and 9-anthraldehyde azine (3) is thermally reversible. The thermal reaction gives the same isomers as the photochemical reaction. We have studied the mechanism of the thermal isomerisation of these azines. Our results are in accordance with an inversion of the N atom which is connected with a rotation movement about the N-N single or the CN double bond.

Thermochromism and photochromism of aryl-substituted acyclic azines II: Photokinetics

Abstract Acyclic azines with higher condensed aromatic and heterocyclic substituents are photochromic and show both thermal isomerization and photochemical isomerization. From the point of view of formal kinetics the azines can be divided into four reaction types depending on the substituents R i . The correspondence of the expected formal kinetic behaviour of the azines with the experimental results is a direct proof of a photochemical E – Z isomerization of these compounds. We investigated acyclic azines which fulfil all criteria of a complicated unitary photoreaction of the type A ⇌ B as well as those azines showing a reversible consecutive photoreaction A ⇌ B ⇌ C. All quantum yields were determined using formal kinetics.

Thermochromism and photochromism of aryl-substituted acyclic azines III: Investigations on the mechanism of photochemical isomerization

Abstract We studied the reaction mechanism of the unsensitized as well as the sensitized photochemical E — Z and Z — E isomerizations of benzophenone-9-anthraldehyde azine. The photochemistry of this compound follows a unitary E ⇌ Z reaction. For qualitative investigations we used benzophenone-9-acridinealdehyde azine, 9-anthranyl-2-pyridinealdehyde azine, 9-anthranyl-3-quinolinealdehyde azine, 9-anthranyl-9-acridinealdehyde azine and 9-acridinealdehyde azine. The experimental results are consistent with the following mechanism for the photoisomerization of azines. In the photochemical E — Z isomerization the S 1 state of the E isomer is reactive; sensitization of the triplet state does not induce the reaction. A singlet mechanism is also very probable for the Z — E isomerization. The most effective photophysical processes competing with isomerization are intersystem crossing in the E isomer and radiationless internal conversion in the Z isomer.

Thermochromism and photochromism of aryl-substituted acyclic azines VII: solvent effect on photochemical E-Z isomerization

Abstract In the E-Z isomerization of benzophenone-9-anthraldazine and benzophenone-9-acridinealdazine there is a significant relation between φE → Z and the solvent acceptor number AN, whereas a significant relation between φZ → E and AN could not be detected. These results are interpreted in terms of the effect of solvent polarity on the energy levels of the E-Z isomers of the azine.

Correlative studies of some spectroscopic and bonding parameters in octahedrally coordinated metal carbonyl complexes

Abstract Empirical correlations between infrared absolute intensity of CO-stretching modes and ionization energy and MC and CO bond polarizability derivatives and 13C-chemical shifts and charge-transfer spectra CT, and calculated 2π-bond population on CO-group in octahedrally coordinated metal carbonyls are discussed and rationalizations of bonding sequences are suggested using data in the literature and new data obtained in this laboratory. The results support the suggestion that the intensity should be a more sensitive measure of the importance of π-bonding in complexes of this type than the CO stretching force constant. The results obtained are discussed in terms of orbital energetics and electronic distribution. Additional considerations are the mass spectral features of several monosubstituted group VIB metal carbonyls and the relative strength of the L-M+ bond from the relative abundances of ions.

Thermochromism and photochromism of aryl- substituted acyclic azines V: Quenching of the photochemical EZ isomerization via Förster energy transfer

Abstract The EZ isomerization of benzophenone-9-anthraldehyde azine is quenched by dyes of appropriate singlet energy. The quenching occurs predominantly via Forster energy transfer. The development of a procedure that allows a distinction to be made between direct and sensitized fluorescence for the case of a non-fluorescing donor (azine) and overlapping donor and acceptor spectra is reported.

Quenching of the fluorescence and the formation of exciplexes of thioindigo by aromatic electron donors

Abstract In aliphatic solvents fluorescence quenching of thioindigo is diffusion-controlled by aromatic electron donors with ionization energies