Aleksander Siemiarczuk

A novel approach to analysis of pyrene fluorescence decays in sodium dodecylsulfate micelles in the presence of Cu2+ ions based on the maximum entropy method☆

Abstract The maximum entropy method (MEM) has been used to analyze fluorescence decays of pyrene quenched by Cu 2+ ions in micellar SDS solutions. Two new methods for precise determination of kinetic parameters have been introduced. The Poisson distributions of preexponential factors have been recovered explicitly from the fluorescence decay data.

Fluorescence decay kinetics of 1,3-di(1-pyrenyl)propane reinvestigated

Abstract The decay kinetics of the monomer fluorescence band of 1,3-di(1-pyrenyl) propane has been studied by the time-correlated single-photon counting technique. Analysis by the exponential series method has revealed an existence of a short-lifetime distribution in addition to two longer-lived fluorescence components. This is in contradiction with the previous reports, in which authors claimed the existence of three discrete lifetimes for this compound.

Fluorescence lifetime of chlorophyll a in pure and mixed langmuir-blodgett films

Abstract Fluorescence lifetimes of pure chlorophyll a monolayers were determined by single-photon counting and by picosecond spectroscopy. Neither technique could resolve its very fast decay rate, attributed to a high aggregate concentration and rapid intermolecular energy transfer. The same experiments were performed on monolayers of chlorophyll a diluted with phospholipids at a molar ratio of 1 to 100. From the single-photon counting decay curves, two fluorescence lifetimes were deconvoluted, i.e. 4.9 and 2.3 ns, indicating the presence of monomeric and aggregated chlorophyll a, respectively. They differ somewhat from the picosecond spectroscopic result where only one lifetime at 3.3 ns was calculated. This is indicative of an exciton annihilation process since it is smaller than the average of the single-photon counting lifetimes. Fluorescence spectroscopy was also used to better understand the photophysics of the chlorophyll a monolayer.

Recovery Of Underlying Distributions Of Lifetimes From Fluorescence Decay Data

This paper discusses the problem of fluorescent molecular systems where the complexity of the molecule or its environment give rise to distributions of decay times rather than discrete two- or three-component decay behavior. The Exponential Series Method for distribution recovery is examined and examples from recent work presented.

Light-induced intramolecular electron transfer from a porphyrin linked to a p-benzoquinone by a rigid spacer group

A model of the reaction center in photosynthesis is described which consists of a tetra-arylporphyrin attached to a p-benzoquinone through a bicyclo[2.2.2]octane; fluorescence lifetime data suggest that visible light induces intramolecular electron transfer between the porphyrin and the quinone is much less efficient than in previously reported linked porphyrin–quinone molecules and indicate that it is subject to a novel solvent effect.

Recovery Of Fluorescence Lifetime Distributions Generated By Heterogeneous Systems

The Maximum Entropy Method and a new Exponential Series Method are described and tested for the recovery of underlying fluorescence lifetime distributions from digital fluorescence decay data. These two numerical techniques are applied to two heterogeneous systems, the intramolecular quenching in 1,3-di(1-pyrenyl)propane and the cupric ion quenching of pyrene in a sodium dodecyl sulfate micellar system. In the former, the short lifetime region is characterized by a broad distribution, which as the temperature is lowered, shifts dramatically to long lifetimes. In the micellar system, a lifetime distribution following the predicted Poisson distribution is recovered at each of five cupric ion concentrations, a result that supports the model of quencher ions distributed in the micelles according to Poisson statistics.

Spectroscopic and Electrochemical Studies of Photochemical Electron Transfer in Linked Donor-Acceptor Molecules

Some covalently-linked porphyrin-quinone (PQ) molecules of restricted molecular geometry are described. The excited state P*Q, Where P* is the porphyrin S1 state, probably undergoes intramolecular electron transfer to produce the charge-separated state P†Q. The forward rate constant et f at 295 K for this electron transfer, measured from fluorescence quenching in PAQ (Scheme 1) compared with its hydroquinone analogue PAQH2, lies in tne range (1 − 230) × 107 s− and is strongly solvent dependent. The electrochemically measured energy U± of P†Q with respect to the ground state PQ is 1.35 – 1.41 eV and is also somewhat solvent dependent. Rationalization of the solvent dependence of k et f and of U± is attempted both in terms of the Marcus theory of electron transfer and in terms of the Onsager reaction field theory; the latter appears to be more successful.