We introduce novel statistical copolymers of poly(9,9‐dioctylfluorene), PFO, which contain various concentrations of 6,6′‐(2,2′‐octyloxy‐1,1′‐binaphthyl) spacer groups. We demonstrate that, owing to the large dihedral angle (> 60°) between neighboring naphthalene units, we could hinder the formation of the highly ordered β‐phase in thin films of the copolymers. In low‐temperature photoluminescence measurements, the typical signature of the PFO β‐phase at 442 nm is no longer observed for copolymers with a binaphthyl concentration of about 12 %. Moreover, the optical properties of the copolymers resembled those of the glassy α‐phase PFO. Second‐order distributed feedback (DFB) lasers based on thin films of the homopolymer PFO showed a minimum lasing threshold of 11.7 μJ cm–2 (λmax = 452 nm, excitation at λ  = 337 nm with 500 ps pulses). With increasing binaphthyl concentration in the copolymer backbone, the lasing threshold steadily decreased to 3 μJ cm–2 for a binaphthyl concentration of about 12 %. Therefore, our novel copolymers provide a vast improvement for PFO‐based optoelectronics.

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Admittance spectroscopy is a simple yet powerful tool to determine the carrier mobility of organic compounds. One requirement is to have an Ohmic contact for charge injection. By employing a thin interfacial layer of tungsten oxide, or molybdenum oxide we have found a possibility to efficiently inject holes into organic materials with a deep highest occupied molecular orbital level down to 6.3eV. These results considerably enhance the application range of the admittance spectroscopy method. The measured data are in excellent agreement with data obtained by the time-of-flight technique.

We present a series of low-molecular-weight materials based on cyclic phosphazenes for the use as host materials in blue phosphorescent organic light-emitting diodes. Substituted phenyl rings are attached to the central phosphazene ring either via phosphorus–oxygen bonds to yield phenoxy-substituted derivatives or via direct phosphorus–carbon bonds to yield phenyl-substituted derivatives. The phenoxy substituted cyclic phosphazenes were prepared by nucleophilic substitution of the six chlorine atoms in hexachlorocyclotriphosphazene with phenoxy groups, whereas the phenyl substituted cyclic phosphazenes were formed in a cyclocondensation reaction of three equivalents of substituted phosphinic amides. The phenyl substitution leads to materials with superior thermal properties compared to the phenoxy substitution. Because of the nonconjugated linkage to the phosphazene core, the host materials have very high triplet energies of more than 3 eV. In an OLED device using one compound as host for the saturated blue phosphorescent emitter Ir(dbfmi), a peak power efficiency of 7.6 lm W–1 and a peak luminance of 5000 cd m–2 were achieved.

Our investigations refer to highly efficient emitting materials used in organic light-emitting diodes (OLED). We are especially interested in the possibility of shifting the emission wavelength in phosphorescent iridium(III) complexes. Depending on the mesomeric and inductive behavior of different substituents, the emission spectrum can be varied by introducing those substituents at various positions of the chromophoric ligand. Therefore, we synthesized Ir(ppy) 3 -analogue complexes with nitrile, trifluoromethyl and methoxy groups at different positions of the ligand's phenyl ring to determine the influence of the position and of each substituent on the emission spectrum. To further study the adjustability we prepared several heteroleptic complexes and changed the ancillary ligand therein. In addition, we developed a new and as yet unknown ligand system based on hetero five membered rings, cyclometalated to iridium to generate homo-and heteroleptic complexes. Devices obtained with these emitting materials have shown high luminescence efficiencies of up to 30 lm/W @ 500 cd/m².