M. Hauser

Diffusion and long-range energy transfer

Abstract Based on a pair probability method for the statistics of resonance energy transfer the effect of additional diffusion is studied. Simple approximate formulae for luminescence quenching are derived and compared with results previously given in the literature.

Theoretical and experimental investigations of combined diffusion and long-range energy transfer

Abstract An improved expression for the effective interaction radius is derived for the general case of energy transfer accompanied by diffusion. The donor fluorescence decay of pyrene/perylene in 1:1 paraffin oil/1-methylnaphthalene supports the theory.

Diffusion-controlled reaction kinetics in micelles

Abstract The rate of diffusional encounters between two species confined pairwise in small spherical volumes is investigated by means of computer simulation and approximate analytical analysis. Such systems consisting of cage type subsystems with two reactants occur in the case of micellar solubilized partners of a diffusion-controlled reaction. It is shown that the rate of encounter or reaction is, to a good approximation, that of a homogeneous solution reaction where one molecule per volume is the effective concentration.

Substituent effects on triplet yields in aminoanthraquinones : radiationless deactivation via intermolecular and intramolecular hydrogen bonding

Abstract The dependence of the triplet quantum yields of monosubstituted and disubstituted aminoanthraquinones on the number of substituents and on their position was studied. Using fluorescence lifetimes, fluorescence quantum yields and triplet quantum yields, the rate constants of the intersystem crossing into the triplet state and of the internal conversion into the ground state were evaluated. For monosubstituted aminoanthraquinones the individual contributions of various mechanisms to the internal conversion have been estimated. In quenching the excited singlet state, intermolecular hydrogen bonding to the solvent is more efficient by an order of magnitude than intramolecular hydrogen bonding.

Determination of the rotational diffusion by a picosecond phase fluorometer

Abstract The rotational diffusion of the oxypyrenetrisulphonate anion (OPS) in aqueous solution has been studied by measuring the time dependent fluorescence depolarization with a phase fluorometer. In the temperature region from 10 to 95°C the relaxation times vary between 136 and 26 ps. Comparison with the theory shows that the rotating volume is a sphere containing the OPS molecule and about 10 water molecules.

The Coulomb cage pair

Abstract The separation of initially induced ion pairs into free ions in solution is discussed theoretically by means of numerical calculations of the partial differential equation for diffusion in a Coulomb field. The theory is compared with simple approximation formulae and previously published experimental data.

Kinetic analysis of the abnormal fluorimetric titration behaviour of naphthylamines

Abstract The fluorimetric titration behaviour of naphthylamines is abnormal in that the sum of the reduced quantum yields of conjugated acid and base passes through a minimum. Based on fluorescence quantum yield and lifetime measurements, we explain this behaviour by two independent mechanisms: A diabatic quenching of the excited base by protons and a decrease of the excited cations protolytic dissociation in the hyperacidic region. Though apparently independent processes, their rate constants can be shown to be related to each other by a quasi-thermodynamical equation.

1-Pyrene sodium sulphonate in inverse micelles. Absorption and emission studies

Abstract The absorption and fluorescence spectra of 1-pyrene sodium sulphonate were measured in water and in the system benzene/cetyldimethylbenzylammonium chloride/water, which forms micelles with an aqueous interior. From the large solvent effect on the oscillator strength of the L b band, which is in accordance with the measured fluorescence lifetimes and quantum yields, it is to be concluded that the solute is incorporated in the detergent layer of the inverse micelles.

Investigation of the internal mobility of triton X 100 micelles by fluorescence anisotropy and excimer probing

Abstract The rotational and translational mobility of various fluorescent probes in micelles of Triton X 100/water is unexpectedly higher than in the pure liquid detergent. The intramicellar mobility of small probes is higher than that of larger probes and is still pronounced well below the freezing point of the pure detergent. This peculiar intramicellar mobility near the freezing point is reflected by fluorescence anisotropy and excimer formation. The rotational mobility, which is spherical in homogeneous solution, is anisotropic in the micelles, but this behaviour is not pronounced.

Excimer Formation of 1-Pyrene-Sodium Sulphonate in Inverse Micelles

Abstract Micelle aggregation numbers may be obtained from the fluorescence time dependence of excimerforming solubilised substances. The micellar system cetyldimethylbenzylammonium chloride (CDBA)/water/benzene was studied using 1-pyrene sodium sulphonate as the fluorescent probe. Solubilised water increases the CDBA aggregation number. It is shown that the micelles are poly-disperse at lower CDBA concentrations. The influence of concentration and aggregation number on the photostationary excimer/monomer fluorescence intensity ratio of the solubilised probe is discussed.