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 derivatives, 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 π-π* 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 substituted polyfluorenes are mainly caused by a helical conformation of the conjugated polymer backbone.

The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume–pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K0 = 8.6 GPa and K′0 = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure-induced shift of the Raman modes to higher frequencies. The mode Grüneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied.

The dependence of fluorescence quantum yields and S

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