Copolymers of 2-(9H-carbazol-9-yl)ethyl 2-methylacrylate and 4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl 2-methylacrylate: correlating hole drift mobility and electronic structure calculations with electroluminescence.

Methacrylate monomers functionalized with pendant carbazole and oxadiazole moieties were copolymerized into random copolymers with varying carbazole/oxadiazole ratios. Specifically, the monomers of 2-(9H-carbazol-9-yl)ethyl 2-methylacrylate (CE) and 4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl 2-methylacrylate (tBPOP) were copolymerized in various ratios, and the inherent hole drift mobilities were assessed through time-of-flight techniques. At a field strength of 345 kV/cm, the homopolymer PCE exhibited a hole mobility of 5.9 x 10(-7) cm(2)/V.s, which was approximately twice the value of the technologically important poly(9-vinylcarbazole), which exhibited a value of 2.8 x 10(-7) cm(2)/V.s. The range of hole mobilities in the copolymers varied from 2.4 x 10(-8) cm(2)/V.s for copolymers containing 50 mol % of the carbazole-containing monomer residue to 3.0 x 10(-7) cm(2)/V.s for copolymers that incorporated 88 mol % of the residue. Density functional theory (B3LYP/6-21G*) and optical absorption derived highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of CE were -5.39 and -1.94 eV, respectively, while the corresponding oxadiazole monomer (tBPOP) had a HOMO energy of -5.99 eV and a LUMO energy of -2.23 eV. The mean luminous efficiency of coumarin 6 doped single-layer devices constructed from the poly(CE-co-tBPOP) copolymers indicated a relatively flat efficiency of ca. 0.25 cd/A over a wide carbazole mole fraction content of 0.30-0.70.

Optical amplification in a first-generation dendritic organic semiconductor.

We report a study of a new class of organic semiconductor as an optical gain medium. We demonstrate amplification of violet light by use of stimulated emission in a solution of a first-generation bis-fluorene-cored semiconducting dendrimer. Amplification is also observed in the solid state by means of amplified spontaneous emission in an optically pumped dendrimer planar waveguide. Gains of 36 dB cm(-1) at 420 nm and 26 dB cm(-1) at 390 nm in solution and 350 dB cm(-1) in the solid state are obtained. These results show that semiconducting dendrimers have potential as visible laser and amplifier materials.

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models.

The one-dimensional diffusion equation governing holographic grating formation in photopolymers, which includes both nonlocal material response and generalized dependence of the rate of polymerization on the illuminating intensity, has been previously solved under the two-harmonic expansion assumption. The resulting analytic expressions for the monomer and polymer concentrations have been derived and their ranges of validity tested in comparison with the more accurate numerical four-harmonic case. We used these analytic expressions to carry out a study of experimental results presented in the literature over a 30-year period. Automatic fitting of the data with these formulas allows material parameters, including the nonlocal chain-length variance sigma, to be estimated. In this way, (i) a quantitative comparison of different materials can be made, and (ii) a standard form of experimental result presentation is proposed to facilitate such a procedure.