Biomedical subjects

F Cichos

Publications and source records attributed to F Cichos.

3 recordsLinked to original sources

PubMed2005

Nanoassemblies designed from semiconductor quantum dots and molecular arrays.

The formation of nanoassemblies of CdSe/ZnS quantum dots (QD) and pyridyl-substituted free-base porphyrin (H(2)P) molecules has been spectroscopically identified by static and time-resolved techniques. The formation of nanoassemblies has been engineered by controlling the type and geometry of the H(2)P molecules. Pyridyl functionalization gives rise to a strong complex formation accompanied by QD photoluminescence (PL) quenching. For some of the systems, this quenching is partly related to fluorescence resonance energy transfer (FRET) from the QD to H(2)P and can be explained according to the Förster model. The quantitative interpretation of PL quenching due to complexation reveals that (i) on average only about (1)/(5) of the H(2)P molecules at a given H(2)P/QD molar ratio are assembled on the QD and (ii) only a limited number of "vacancies" accessible for H(2)P attachment exist on the QD surface.

Journal Article↗

PubMed2003

Anisotropic diffusion of single molecules in thin liquid films.

Single molecule wide field imaging is applied to study the diffusion in ultrathin liquid films on solid surfaces. The results show a broad distribution of diffusion coefficients. This is tentatively ascribed to an anisotropy of the diffusion coefficient perpendicular to the surface and a slow exchange of molecules between regions of different diffusion coefficients. We have evidence, that these changes as well as the slow motion perpendicular to the surface are related to the molecular layering of the liquid close to the surface.

Journal Article↗

PubMedDate not supplied

Investigation of tetherable distilbazolium compounds as fluorescent probes in nanostructured silica sol-gel materials.

Distibazolium dyes are investigated by steady-state and time-resolved fluorescence techniques in a series of low- and high-viscosity polar solvents and in a silica sol-gel matrix. In all solvents and the sol-gel matrix, an interplay of photoinduced switching between different cis-trans isomers and solvation dynamics is observed. Even in a viscous solution (glycerol) and in silica gel, cis-trans isomerization is solvent-controlled. Whereas in glycerol the solvation results in a time-dependent fluorescence Stokes shift, the solvation-induced spectral heterogeneity in silica gel is mostly static, possibly due to a close proximity of dye molecules to the silica surfaces of the nanopores. Compared to low-viscosity solvents, where the cis-trans isomerization process takes place with a solvent-dependent rate on the timescale of about 120-150 ps, it slows down to about 1100-1400 ps in glycerol and about 1500 ps in a sol-gel matrix. Additionally, fluorescence kinetics of the dyes in the sol-gel reveals the presence of a range of different "frozen-in" conformers exhibiting a broad spectrum of lifetimes from 20 to 300 ps.

Journal Article↗