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Dense chromophore systems have been proposed as an alternative approach to creating solid-state triplet–triplet annihilation upconversion (TTA-UC) materials. In order to extend this system to polymer-based TTA-UC materials, a new method for the in situ preparation of dense chromophore systems in poly(vinyl alcohol) (PVA) was developed using a mechanical stretching technique. The chromophores used in this study were newly synthesised to dissolve homogeneously in a PVA aqueous solution. These chromophores exhibited a blue upconverted emission in MeOH solution upon excitation with a 532 nm green laser. Remarkably, a clear upconversion emission was observed from the chromophore-blended PVA films even under ambient conditions after the stretching process. In addition, a correlation between the elongation length of the films and the ratio of UC emission/phosphorescence was clearly observed. The stretching process made the chromophores more condensed in the oriented and cross-linked polymer chains, thereby creating favourable conditions for triplet–triplet annihilation.

A novel functionalized cellulose derivative, 6-O-[4-(9H-carbazol-9-yl)butyl]-2,3-di-O-methyl cellulose, has been synthesized and characterized. The photoluminescence spectrum of the as-cast film of the cellulose derivative exhibits sharp peaks with a well-defined vibronic structure, which indicates that the interaction between carbazole groups is rather weak. This is in contrast to the broad spectrum of a poly(N-vinylcarbazole) thin film. A thin-film device, where the cellulose derivative is sandwiched by two different metals, shows a drastic transition between low- and high-conductivity states upon the forward and backward sweeping of an external electric field. This reversible current density transition behavior demonstrates a typical memory characteristic, with the ON/OFF (high- and low-conductivity) states exhibiting a current ratio of about four orders of magnitude. The cellulose derivative with a functional group such as a carbazole moiety will be a candidate for organic electronic materials.

The structure inhomogeneities and dynamic fluctuations in poly(N-isopropylacrylamide) (PNIPA) gels have been investigated by dynamic light scattering as a function of gel-preparation pressure, Pprep. The ensemble average light scattered intensity (〈I〉E), a measure of structure inhomogeneities, was found to be an increasing function of Pprep and diverged at Pprep = 168 MPa. This indicates that PNIPA gels undergo phase separation by increasing Pprep. The corresponding PNIPA solution was transparent and had no Pprep dependence. It is concluded that the structure of gels depends not only on the pressure at observation Pobs but also on Pprep, and the inhomogeneities increase with Pprep. On the other hand, the dynamic fluctuations were independent of Pprep. This shows that cross-linking plays a major role in formation of built-in structure inhomogeneities.

We fabricated organic field-effect transistors (OFETs) based on benzodithiophene (BDT)-dimer films by vacuum evaporation. The surface of the BDT-dimer films deposited on a SiO2 gate insulator was so rough that excellent FET characteristics were not obtained. However, the surface morphology of the films deposited on poly(methyl methacrylate) buffer layers was significantly improved, and dense grains of submicron size were formed. Grain size increased from the submicron scale to the micron scale by reducing growth rate from 0.035 to 0.02 nm/s. The fabricated OFETs have shown p-type FET characteristics with a carrier mobility of 0.016 cm2 V-1 s-1. More importantly, it has been demonstrated that the performance of the BDT-dimer OFET is much more stable in air than that of the pentacene OFET.

Pressure dependence of the Flory-Huggins interaction parameter for poly (N-isopropylacrylamide)/water gel is obtained by measuring the swelling ratio of the gel in equilibrium under hydrostatic pressure up to about 100 MPa and by employing a mean field theory based on the Flory-type of the Gibbs free energy formula. The interaction parameter strongly depends on the volume fraction of a gel network and also on solvent pressure. In the swollen phase equilibrium of a gel under pressure, both the enthalpy and entropy increase with pressure, the second virial term decreases inversely and the interaction parameter is an increasing function of pressure. It can be seen that hydrostatic compression strengthens the hydrophobic interaction between polymer segments because of a loosening hydrogen-bond structure near the monomer unit.