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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.

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.