The dependence of fluorescence quantum yields and S₁ - lifetimes of donor-acceptor substituted trans-stilbenes on temperature were measured in the temperature range from 298 to 100 K, using solutions of stilbenes in 3-methylpentane (3-MP). Measurements of fluorescence and phosphorescence spectra show that the energy is nearly independent of the acceptor. As the S₁ - energy decreases with increasing acceptor strength, the S₁ - T₁ energy gap decreases with increasing acceptor strength. For all compounds intersystem crossing (ISC) S₁ - T₁ is negligible.

The association of complex formation to static quenching in CT-systems was investigated. Evaluation of data made evident that the inner filter effect (IFE) has to be allowed for.
Time resolved and temperature dependent stationary measurements of fluorescence led to the separation of dynamic and static quenching components. The static quenching constant was discussed with respect to the equilibrium constant of complex formation determined by absorption spectroscopy.

For years, there has been a controversial discussion on the subjekt of the relation between the thermodynamics association constant of charge transfer complex formation and the constant of static quenching of fluorescence. Starting from the current state of this discussion it was our concern to carefully investigate all the occuring effects which influence the measured experimental quantities and which have to take into account for finding the constants. For determination of equilibrium constants we studied:

activity constants,

concurrent formation of complexes of different stoichiometry,

specific effects of solvents,

influence of temperature.

Except for activity constants, it can be assumed that the effects change the spectral band profile. The latter was analysed in order to find out about stoichiometry and equilibrium constants. For the band profile analysis a profile function was applied which was set up by us on the grounds of our previous work in the field.
Activity coefficients were calculated using vapor pressure measurements. For finding the association enthalpy the temperature dependence of the equilibrium constant was studied. Refractive index and density were also corrected.
As for the investigation of fluorescence quenching by charge transfer interaction, stationary as well as time resolved measurements in dependence of temperature were performed. The separate determination of the dynamic quenching constant through measeruments of fluorescence lifetimes allowed an accurate assessment of the static quenching component in the overall quenching process. The procedure required that the measured values were corected for all diminant experimental errors. We consider our extended approach to corrections for the inner filter effetcs as an important addition to experiment evaluation hitherto described in publications. Many a quencher used in fluorescence experiments exhibit absorption in the region of excitation and / or in the region of emission of the fluorescence compound. We developed an effective approach with which a quantitative correction for both effects becomes possible.
From the comparative study of the equilibrium constant of complex formation found by absorption spectroscopy with the constant of static fluorescence quenching the relations K_stat < K_CT and DG_CT < DG_stat arise. From this a proposal for a reaction scheme ensues that leads to a deeper insight into charge transfer ground state interaction.

Two differently substituted crystalline 2,5-diphenyl-1,34-oxadiazole compounds are investigated in the pressure range up to 5 GPa. Phase transitions are detected using Raman and X-ray investigations.

The dependence of the fluorescence of 2,5-diphenyl-1,3,4-oxadiazole (DPO) crystals under compression up to 7 GPa was experimentally studied. The knowledge of the structural behavior at high pressure allows to relate the variation of the fluorescence to the diminution of the inter-molecular distance.

The dependence of the fluorescence of 2,5-diphenyl-1,3,4-oxadiazole (DPO) crystals under compression up to 7 GPa was experimentally studied. The knowledge of the sturcutral behavior at high pressure allows to relate the variation of the fluorescence to the diminution of the inter-molecular distance.

Liquid-crystalline polyfluorene (PF) homopolymers substituted with chiral alkyl side chains were synthesized, and their chiroptical properties in the solid state were investigated by means of circular dichroism (CD), circularly polarized photoluminescence (CPPL) and circularly polarized electroluminescence (CPEL) measurements. Polarization-selective scattering of light is shown to cause artifacts in the circularly polarized absorption and emission spectra in the wavelength range near or above the absorption edge, and a measurement scheme to avoid these is presented. For all derivates, significant chiroptical effects appeared only after the solid layers have been annealed at elevated temperatures, preferably into the liquid-crystalline state of the polymer. The largest anisotropy factors were measured for a polyfluorene substituted with chiral (R)-2-ethylhexyl side chains, yielding absolute values of up to 0.28 for CPPL and up to 0.25 for CPEL. These are among the highest ever reported for a chiral conjugated polymer. Anisotropy factors for CD, CPEL, and CPPL were consistently found to follow an "odd-even effect" concerning the position of the chiral center in the alkyl side chain. If the chiral center is placed close to the polymer backbone, the CD is dominated by one peak with its maximum close to the maximum of the pi - pi* absorption band. This indicates that the chiroptical properties are most probably caused by intrachain effects rather than by pure interchain exciton coupling. This interpretation is supported by the results of time-dependent Hartree-Fock calculations for the isolated fluorene dimer and trimer. In both cases, the anisotropy factor depends strongly on the torsion angle between neighboring fluorene units. For the trimer, a maximum anisotropy factor of 0.25, close to the maximum values determined experimentally, is predicted for a torsion angle of ca. 105°. Both experimental and theoretical results indicate that the chiroptical properties of these chiral substitutes polyfluorenes are mainly caused by a helical conformation of the conjugated polymer backbone.