We present time-resolved photoluminescence measurements on a range of poly- and oligofluorenes with different molecular weights in both dilute solution and thin films. The commonly observed parasitic broad green emission band, which has previously been attributed to an excimer, is identified in all solution and film samples and assigned to an on-chain emissive defect. By comparison of the luminescence decay in the solid state at different temperatures it is shown that, at room temperature, intramolecular relaxation is faster in these polyphenylenes than intermolecular exciton diffusion.

The synthesis of the azobenzene gelator has already been reported [10a]. To prepare a self-assembled cholesteric gel, a homogeneous mixture of BL006/ R811/gelator was obtained by first dissolving all compounds in a common solvent, tetrahydrofuran (THF), and then evaporating the solvent under reduced pressure. The mixture was flow-filled, at 130 C, into the 10 lm thick electrooptic cell, and subsequent fast cooling of the mixture to room temperature resulted in the gel sample with a uniform physical network built up from nanometer-sized hydrogen-bonded fibrous aggregates (Fig. 1a). To record a grating, a photomask was positioned on one side of the cell, and the whole was placed into a thermostat hot stage and heated to the recording temperature. A curing system (Novacure apparatus) was used to expose the sample to UV light centered at 360 nm. Once the irradiation was completed, the sample was cooled to room temperature, either under irradiation or with irradiation turned off. The gratings were observed on a polarizing optical microscope (Leitz DMR-P apparatus). For SEM observations of the aggregates, on a Hitachi S-4700 FEG SEM apparatus, the cell was carefully opened and the cholesteric LC host was extracted in hexane.For the measurements of the diffraction efficiency under an electric field, a He±Ne laser (633 nm) was used as the incident light source (normal to the cell) and the 1st order (+1) diffraction signal, I d , was monitored using a high-speed photodetector (Displaytech) collected to a digital oscilloscope (Tektronix, TDS 420 A apparatus). A high-voltage waveform generator (WFG500 apparatus, FLC Electronics) was used to apply the AC (1000 Hz), square wave, and pulse electric fields through the cell. The diffraction efficiency was calculated as the ratio of I d over the intensity of the laser beam before reaching the cell.

As the color palette of available solution processable electrochromic polymers expands, there has remained the need for red, orange, and yellow to transmissive switching materials. Here we report on the synthesis and characterization of two such polymers, the orange to transmissive switching (poly{3,4-di(2-ethylhexyloxy)thiophene}) electrochromic polymer-orange (ECP-orange) and the red to transmissive switching processable polymer (poly{3,4-di(2-ethylhexyloxy)thiophene-co-3,4-di(methoxy)thiophene}) electrochromic polymer-red (ECP-red). The ECP-orange has a bandgap of 2.04 eV, an absorption λ max centered at 483 nm, and an E 1/2 of 0.37 V versus Ag/Ag þ . The electrochromic contrast is 48% T at 483 nm with a time to reach 95% of the full optical contrast of 5.3 s for a film that has an absorbance of 0.98 au at λ max . Because of steric relaxations from the random copolymerization of a branched dialkoxy-substituted thiophene with a dimethoxy-substituted thiophene, the red to transmissive switching ECP-red has a bandgap of 2.00 eV, a λ max red-shifted by 42 to 525 nm, and an E 1/2 decreased to 0.21 V versus Ag/Ag þ . Additionally, the red polymer has a higher contrast of 60% T and a shorter time to reach 95% of the full optical contrast of 2.3 s. These two reported polymers allow the field of electrochromics to come closer to a full set of fully solution processable materials that yield films whose optical absorption covers the full visible spectrum while switching to a highly transmissive oxidized state as needed for full color displays.

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