We demonstrate up-conversion of noncoherent sunlight realized by ultralow excitation intensity. The bimolecular up-conversion process in our systems relies on the presence of a metastable triplet excited state, and thus has dramatically different photophysical characteristics relative to the other known methods for photon up-conversion (two-photon absorption, parametric processes, second harmonic generation, sequential multiphoton absorption, etc.).

Highly polarized electroluminescence from a liquid‐crystal polymer device, based on a branched polyfluorene with a branched side chain, is demonstrated here as a further step towards the use of organic electroluminescent (EL) devices as backlights in conventional liquid‐crystal displays. The modification of a polyimide (PI) for hole conduction by addition of a suitable filler at moderate concentration is reported and the performance of a device containing such a rubbed, hole‐conductor‐filled PI layer as the alignment layer is compared with that of a device with a PI‐only alignment layer.

Efficient deep‐blue electroluminescence(EL) is obtained via end‐capping polyfluorene (PF) homopolymers with hole‐transporting moieties (HTMs). Strong evidence that the observed improvement in device performance is related to the end‐capper moieties comes from the comparison of two different end‐cappers. The HTM does not disturb the liquid‐crystal properties of the PF polymer. Using doped polyimide alignment layers, polarized light‐emitting diodes (LEDs) with a polarization ratio in excess of twenty at an efficiency of 0.25 cd/A could be realized.

Spin-coated films of an ethylhexyl derivative of polyfluorene can be converted on a pretreated polyimide substrate into highly oriented films by annealing in the liquid crystalline state. Together with improving orientation segregation of the wormlike molecules with respect to chain lengths and lamella formation proceeds. End groups are preferentially assembled in interlamellar regions. This morphological feature is thought to influence all measurements of intrinsic properties of polyfluorene films with similar histories. Electron diffraction patterns of the film are identical with X-ray fiber diagrams of fibers drawn from the melt and annealed in the liquid crystalline state. The experimental data show that the polymer molecules adopt a helical (5/q) conformation, packing in a trigonal unit cell. Molecular modeling based on ab initio MO calculations have been carried out to obtain independent estimates of chain geometry and conformation. These calculations are more in favor of a 5/2 rather than a 5/1 helix, with the argument of the observed packing of the individual PF chains and a plausibly low torsion angle of adjacent fluorene building blocks only for a 5/2 helix.

An emitter/sensitizer couple (see picture; C red/green, H white, N blue, Pd gray) was specially designed for the process of noncoherently excited photon up‐conversion. The hypsochromic shift between the energy of the excitation photons and the emitted photons is about 0.7 eV, and an external quantum yield of 0.04 is achieved. As noncoherent excitation source, the near‐infrared part of the solar spectrum was used.