Herein, triplet–triplet annihilation upconversion (TTA-UC) from near-infrared (NIR, 785 nm) to visible (yellow, centered at 570 nm) regions has been demonstrated in the binary solid of condensed chromophores. Microparticles of the binary solid comprising rubrene as a matrix (emitter) and π-extended Pd-porphyrin as a dopant (sensitizer) in a mole ratio of 1000:1 were obtained by solution casting. Excitation intensity dependence and quantum yield (QY) of the upconverted emission were characterized for individual particles under a microscope and revealed a low threshold intensity (∼100 mW/cm2) as compared to the solution and moderate UC-QY (∼0.5%) in the NIR range. The factors contributing to the UC-QY were investigated by time-resolved and steady-state spectroscopies. It was found that the intersystem crossing of the sensitizer, triplet energy transfer, and TTA occurred efficiently in the binary solid, and the fluorescence QY of the emitter governed the UC-QY.

We have been studying oriented thin films of polymers fabricated by the friction transfer method, which allows a variety of conjugated polymers to be aligned into highly oriented films. However, with this method it is difficult to prepare oriented films from a mixture. In this work we prepared oriented thin films of a mixture of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which is a promising combination for application in organic solar cells. We obtained oriented blend films of P3HT and PCBM by the friction transfer method from a solid block prepared from a mixed solution with a weight ratio of 1 : 1. Atomic force microscopy shows that microscale phase separation took place in the blend films. Polarized UV–visible spectra show that the P3HT chains were aligned parallel to the friction direction in the blend films. X-ray diffraction studies suggested that the preferred orientation of P3HT crystallites was the “face-on” orientation in the blend film.

Controlling the molecular orientation of the conjugated oligomer, α-sexithiophene (6T), is crucial to improve organic optoelectronic device performance. Most 6T molecules evaporated onto quartz and SiO(2)/Si substrates orient nearly perpendicular to the substrate. Here, we report the formation of oriented thin films of 6T on in-plane-oriented polythiophene (PT) films formed by the friction-transfer method. 6T was evaporated onto oriented PT films under vacuum. The films were investigated by polarized optical microscopy, polarized ultraviolet-visible light (UV-vis) absorption spectroscopy, and grazing incidence X-ray diffraction measurement (GIXD). In all spectra, larger absorbance derived from PT and 6T was observed, in parallel polarization to the friction direction, compared to that of orthogonal polarization. These results indicate that the 6T molecular axis is aligned in the friction direction (PT chain direction) of PT films. GIXD also confirmed that the 6T molecular axis was aligned parallel to the PT chain axis. In contrast, 6T molecules evaporated onto quartz and poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated silicon substrates aligned nearly perpendicular to the substrate. These results indicate that oriented PT films induce 6T orientation parallel to the PT chain direction.

Control of the molecular orientation of regioregular poly(3-alkylthiophene)s (RR-P3ATs) improves the performance of field-effect transistors and organic photovoltaic devices (OPVs). However, most thiophene ring planes of the RR-P3AT molecules (except RR-poly(3-butylthiophene)) in films formed by the conventional spin-coating method stand on the substrate, that is, edge-on orientation. Orientation control of RR-poly(3-dodecylthiophene) (RR-P3DDT) molecules in films formed by the friction transfer method is reported and the performance of OPVs based on friction-transferred RR-P3DDT films is compared to that of OPVs based on spin-coated films. The films are investigated by polarized ultraviolet-visible light absorption spectroscopy, Fourier transform infrared spectroscopy, and grazing-incidence X-ray diffraction measurement. For friction-transferred films, the RR-P3DDT molecular chain is uniaxially aligned parallel to the substrate plane. In addition, the thiophene ring planes of the RR-P3DDT molecules are also oriented parallel to the substrate plane, that is, face-on orientation. The power conversion efficiency (PCE) and fill factor of the RR-P3DDT/C 60 bilayer OPVs based on the friction-transferred RR-P3DDT films are higher than those of devices based on spin-coated films. The PCE and photocurrent of the device based on the friction-transferred film are larger under irradiation with polarized light parallel to the RR-P3DDT molecular chain direction than with polarized light orthogonal to the chain direction. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40136.

Thin films of a water-soluble poly(phenylenevinylene) (PPV) derivative with sulfonate-containing side chains (DPS-PPV) were formed on silica substrates by a solvent-free friction transfer technique. The films were highly aggregated producing “rods” of polymer aligned perpendicular to the drawing direction. This “log rolling” is in contrast with the reported behavior of most comparable polymers, which tend to align along the drawing direction. The photophysical behavior of the friction-transferred film is also different compared with other film formation techniques of the same polymer. Comparison of the steady-state and time-resolved emission characteristics of these films with films coated by the conventional drop-casting method reveals that short-lived fluorescence components are dominant in the highly aggregated friction-transferred polymer films compared to less aggregated drop-cast films in which long-lived emission species are favored. This highlights the importance of the film formation processes on the properties of the film.