Blue electroluminescent diodes utilizing poly(alkylfluorene) have been demonstrated for the first time. A Schottky-type electroluminescent diode of poly(9,9-dihexylfluorene) is driven at ∼10 V and has a peak emission wavelength of 470 nm at room temperature.

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3‐dodecylthiophene) [P3DT] and poly (3‐hexylthiophene) [P3HT], the temperature dependence of x‐ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit‐cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a‐axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a‐axis direction. (2) The interplanar spacing, intensity, and integral width of the x‐ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x‐ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans‐type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.

We have measured the quadratic electroabsorption ͑EA͒ spectrum of a variety of soluble luminescent and nonluminescent-conjugated polymer films in the spectral range of 1.5-4.5 eV. The luminescent polymers include MEH and DOO derivatives of poly͑phenylene-vinylene͒, poly͑phenylene ethylene͒, and polythiophene; the nonluminescent polymers include poly͑diethynyl silane͒ and monosubstituted polyacetylene. All EA spectra show a Stark shift of the low-lying odd-parity exciton (1B u) and imply the presence of phonon sidebands. There are also higher-energy bands due to transfer of oscillator strength to even-parity exciton states (A g), the strongest of which (mA g) is located at an energy about 1.3 times that of the 1B u exciton in both luminescent and nonluminescent polymers; in the luminescent polymers the EA spectra also show a second prominent A g state (kA g) at an energy of about 1.6 times that of the 1B u. We have successfully fitted the EA spectra by calculating the imaginary part of the third order optical susceptibility, Im͓ 3 (Ϫ;,0,0)͔, using a summation over states model dominated by the ground state, the 1B u exciton, two strongly coupled A g states ͑mA g and kA g ͒, and their most strongly coupled vibrations, using Frank-Condon overlap integrals. A distribution of conjugation lengths, which results in a distribution of excited state energies, was also incorporated into the model. The decomposition of the EA spectra due to the conjugation length distribution was then used to calculate the 1B u exciton polarizability (⌬p) using first derivative analysis. For the longest conjugation lengths in our films, we found ⌬p to be of order 10 4 (Å) 3 in luminescent polymers and 10 3 Å 3 in nonluminescent polymers, respectively, in good agreement with recent subnanosecond transient photoconductivity measurements. We also found that the Huang-Rhys parameter of the 1B u exciton varies between 0.25 and 0.9, being in general smaller for the luminescent polymers. The consequent exciton relaxation energies were calculated to be of order 100 meV. ͓S0163-1829͑97͒03948-9͔

Irradiation W 2 9 0 nm) of an aqueous suspension of poly(p-phenylene) leads to photocatalytic H2 evolution in the presence of triethylamine or diethylamine.

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SYNOPSISConducting polyfluorene derivatives with alkyl chains-poly (9-alkylfluorene) s and poly-( 9,9-dialkylfluorene) s-have been synthesized by chemical polymerization utilizing FeC13 as an oxidizing agent. The polymers obtained are found to be soluble in conventional organic solvents such as chloroform and have been characterized by 'H-and 13C-NMR.The results indicate that the fluorene moeities are mainly linked in the 2,7'-fashion to yield the straight chain polymer. The degree of polymerization is estimated (by gel permeation chromatography) to be of the order of 10. The polymers are found to be fusible and the thermal properties of the polymers have been characterized by differential scanning calorimetry. The glass transition temperature is found to decrease with an increase of the alkyl chain length. 0 1993 John Wiley & Sons, Inc.

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Nematic liquid crystals and smectic liquid crystals can be infiltrated into a three-dimensional periodic array of interconnected nanosize voids in opal films prepared by sedimentation of SiO2 spheres of various diameters. The optical stop band in the transmission spectra of opals shifts drastically by the infiltration of liquid crystals. The stop band is also found to shift at the phase transition points with changing temperature. This effect enables the tuning of optical properties of opals as a prototype tunable photonic crystal. This phenomenon can also be used as a measurement method for the refractive index.