Dieter Kreysig

External heavy atom quenching of the fluorescence of the acridizinium ion via charge-transfer complexes

Abstract The rate constants of fluorescence quenching of the acridizinium ion by alkyl bromides and iodides are determined by the donor behaviour (ionization potential) of the quenches. An encounter-CT complex is postulated, in which the quencher acts as an electron donor.

Photochemistry of substituted cycloheptatrienes XIII: The dependence of quantum yields for sigmatropic hydrogen shifts on the excitation energy☆

Abstract The partial quantum yields in a substituted cycloheptatriene reversible system were measured to determine the dependence on the excitation energy. The quantum yields decrease significantly with increasing excitation wavelength. This is in accordance with the prediction from orbital symmetry considerations for a sigmatropic hydrogen shift. The chemical deactivation from higher excited states is able to compete with internal conversion processes. Furthermore the wavelength dependence of the partial quantum yields is interpreted with two different pericyclic minima in the excited state. The participation of conformers as a possible origin for the wavelength dependence of quantum yields is excluded.

Deactivation behaviour of arenes and heteroarenes. VI. quenching of the fluorescence of heteroarenium cations at high concentrations

Abstract At high concentrations of acridizinium and N-methylacridinium salts in methanol (virtually complete dissociation) a differentiated quenching of fluorescence occurs, since a cation-cation and a cation-anion interaction exist in the excited state. The extent of the fluorescence quenching due to cation-anion interaction is determined by the donor properties of the anions and can be correlated with the corresponding ct-parameters. A fluorescence quenching through cation-cation interaction in the excited state (formation of excimers) is only observed in the case of acridizinium salts. These findings are consistent with the ability of cations to cause photodimerization.