Biomedical subjects

Hans-Joachim Egelhaaf

Publications and source records attributed to Hans-Joachim Egelhaaf.

5 recordsLinked to original sources

PubMed2005

Solid-state optical properties of linear polyconjugated molecules: pi-stack contra herringbone.

The intermolecular arrangement in the solid state and the consequences on the optical and photophysical properties are studied on different derivatives of oligophenylenevinylenes by UV/VIS absorption and angular-resolved polarized fluorescence spectroscopy. Unsubstituted distyrylbenzene (DSB) organizes in a herringbone manner, with the long axes of the molecules oriented in parallel, but the short axes almost perpendicular to each other. Fluorinated distyrylbenzene (F(12)DSB) as well as the DSB:F(12)DSB cocrystals prefer cofacial pi-stacking in the solid state. For all structures, the consequence of the parallel alignment of the transition moments is a strongly blueshifted H-type absorption spectrum and a low radiative rate constant k(F). Significant differences are observed for the emission spectra: the perpendicular arrangement of the short axes in DSB crystals leads to only very weak intermolecular vibronic coupling. Hence the emission spectrum is well structured, very similar to the one in solution. For F(12)DSB and DSB:F(12)DSB, the cofacial arrangement of the adjacent molecules enables strong intermolecular vibronic coupling of adjacent molecules. Thus, an unstructured and strongly redshifted excimerlike emission spectrum is observed. The differences in the electronic nature of the excited states are highlighted by quantum-chemical calculations, revealing the contribution of interchain excitations to the electronic transitions.

Journal Article↗

PubMed2005

Synthesis of axially substituted tetrapyrazinoporphyrazinato metal complexes for optical limiting and study of their photophysical properties.

The synthesis, characterization, and various photophysical properties of axially substituted tetrapyrazinotetraazaporphyrinatotitanium(IV) oxide (Pyz(4)TAPTiO) (1), tetrapyrazinotetraazaporphyrinatovanadium(IV) oxide (Pyz(4)TAPVO) (2), tetrapyrazinotetraazaporphyrinatozirconium(IV) dihydroxide [Pyz(4)TAPZr(OH)(2)] (3) are reported. Nonlinear optical (NLO) properties of Pyz(4)TAPs 1-3 have been evaluated at 532 nm with nanosecond pulses for optical limiting (OL). It is found that the introduction of nitrogen atoms in the condensed rings of the tetrapyrrolic macrocycles together with the presence of axial substituents lead to an improvement of the excited-state absorption properties in comparison to phthalocyanines (Pcs). In the linear optical regime Pyz(4)TAPs 1-3 display a blue shift (about 50-60 nm) of the main UV-vis absorption bands with respect to Pcs and exhibit orange-red fluorescence, which can be observed with the eye in the case of 1. Frontier electronic orbitals of a Pyz(4)TAP could be depicted from available experimental data and the results of density functional theory (DFT) calculations. In the solid state, Pyz(4)TAPTiO (1) displays photoconducting properties.

Indoles↗

PubMed2005

Design of pi-conjugated organic materials for one-dimensional energy transport in nanochannels.

Various end-substituted distyrylbenzenes have been synthesized to serve as guest molecules in inclusion compounds to promote efficient energy transport along one-dimensional channels. Their optical and photophysical properties have been characterized at both experimental and theoretical levels. All molecules display a large transition dipole moment between the ground state and lowest excited state and hence a short radiative lifetime (on the order of 1-2 ns). They also exhibit a large spectral overlap between the emission and absorption spectra, which enables efficient energy transport between molecules arranged in a head-to-tail configuration in nanochannels. Hopping rates on the order of 10(12) s(-1) are calculated at a full quantum-chemical level; this is much larger than the radiative lifetimes and opens the way for energy migration over large distances. Changes in the nature of the terminal substituents are found to modulate the optical properties weakly but to impact significantly the energy transfer rates.

Journal Article↗

PubMedDate not supplied

Structure property analysis of pentamethine indocyanine dyes: identification of a new dye for life science applications.

A collection of nine pentamethine indocyanine dyes was synthesized, and the photophysical characteristics relevant to applications in cell biology and single molecule detection were analyzed in detail. Substituents at the aromatic system covering the auxochromic series and substitutions in the polymethine chain were investigated with respect to absorption and emission spectra, fluorescence lifetimes, fluorescence quantum yields, and fluorescence autocorrelations. Substitutions in the polymethine chain increased the nonradiative energy dissipation of the excited singlet state and decreased the fluorescence quantum yield, relative to the unsubstituted compound. For substituents at the aromatic rings the fluorescence quantum yield negatively correlates with the position of the substituents in the auxochromic series -SO(3)(-), -H, -F, -CH(3). Compounds with sulfonic acid groups or halogen atoms attached to the indolenine systems had the highest fluorescence quantum yields. The compound S0387 had nearly 70% of the quantum yield of Cy5 and comparable photostability. The free carboxylic acid of S0387 was attached to peptides in high yield and purity by established procedures of solid-phase synthesis. The dye-labeled peptides did not aggregate or bind to tissue culture cells and proteins unspecifically. The indocyanine dye S0387 is therefore an attractive new fluorophore for in vitro and cell-based detection of receptor ligand interaction at nanomolar concentrations by flow cytometry, fluorescence correlation spectroscopy, and laser scanning microscopy.

Algorithms↗

PubMedDate not supplied

Understanding supported reactions in spherical compartments: a general algorithm to model and determine rate constants, diffusion coefficients, and spatial product distributions.

A general algorithm allowing the numerical modeling of the time and space dependence of product formation in spherical reaction volumes is described. The algorithm is described by the complete set of mass balance equations. On the basis of these equations, the effects of the diffusion coefficient, reaction rate, bead size, reagent excess, and packing density of the resin beads on the overall reaction rates are determined for second-order reactions. Experimental data of reaction progress are employed to calculate reaction rates and diffusion coefficients in polymer-supported reactions. In addition, the conditions for shell-like product formation are determined, and various strategies for the radial patterning of resin beads are compared. The effect of diffusion on polymer-supported enzyme-catalyzed reactions of the Michaelis-Menten type is treated, as well. Finally, the effects of typical nonideal solid-phase phenomena, namely, the inhomogeneity of rate constants and the concentration dependence of diffusion coefficients, on overall rates are discussed.

Algorithms↗