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Triplet-triplet annihilation photon upconversion (TTA-UC) has received significant attention in energy harvesting applications such as solar cells. The realization of high UC performance in the form of films is a crucial factor for the incorporation of this technology into large-area devices. Herein, we propose a porous UC film, prepared by a simple emulsification method with a poly(vinyl alcohol) (PVA) aqueous solution and a toluene solution of chromophores (rubrene/Pd-tetraphenyl-tetraanthraporphyrin pair) that achieved considerable UC performance in the near-infrared (NIR) (810 nm) to visible (560 nm) range with a maximum quantum yield of 3.7 % (out of 50 %) under an air atmosphere. Notably, the films displayed a clear UC emission when using an NIR light-emitting diode as a low-power-density non-coherent light source, which was confirmed by the naked eye. Excitation-power-dependent time-resolved photoluminescence measurements showed almost identical triplet lifetimes of emitter species for the films and toluene solutions; however, smaller threshold intensities (Ith = 1–2 W/cm2) were observed for the films compared to those of the solutions (Ith = ~10 W/cm2). An evaluation of the remaining toluene in the film and UC emission behavior in liquid nitrogen suggested that the chromophores exist as an amorphous solid in the pores, thus enabling hybrid triplet energy transfer (chromophore-mobility-based and exciton migration) in this unique film. The presented methodology can be generalized to other wavelengths and can enable diverse applications of the TTA-UC technology.

Triplet-triplet annihilation photon upconversion (TTA-UC) has received significant attention in energy harvesting applications such as solar cells. The realization of high UC performance in the form of films is a crucial factor for the incorporation of this technology into large-area devices. Herein, we propose a microporous UC film, prepared by a simple emulsification method with a poly(vinyl alcohol) (PVA) aqueous solution and a toluene solution of chromophores (rubrene/Pd-tetraphenyl-tetraanthraporphyrin pair), which achieved considerable UC performance in the near-infrared (NIR) (810 nm) to visible (560 nm) range with a maximum quantum yield of 7.3 % (out of 100 %) under an air atmosphere. Notably, the films displayed clear UC emission upon using an NIR light-emitting diode as a low-power-density non-coherent light source, which was confirmed by the naked eye. Excitation-power-dependent time-resolved photoluminescence measurements showed almost identical triplet lifetimes of emitter species for the films and toluene solutions; however, smaller threshold intensities (Ith = 1–2 W/cm2) were observed for the films compared to those of the solutions (Ith = ~10 W/cm2). An evaluation of the remaining toluene in the film and UC emission behavior in liquid nitrogen suggested that the chromophores exist as an amorphous solid in the micropores, enabling hybrid triplet energy transfer (chromophore-mobility-based and exciton migration) in this unique film. The presented methodology can be generalized to other wavelengths and can enable diverse applications of TTA-UC technology.

Hemoconcentration membranes used in cardiopulmonary bypass require a pore structure design with high pure water permeability, which does not allow excessive protein adsorption and useful protein loss. However, studies on hemoconcentration membranes have not been conducted yet. The purpose of this study was to analyze three-dimensional pore structures and protein fouling before and after blood contact with capillary membranes using the tortuous pore diffusion model and a scanning probe microscope system. We examined two commercially available capillary membranes of similar polymer composition that are successfully used in hemoconcentration clinically. Assuming the conditions of actual use in cardiopulmonary bypass, bovine blood was perfused inside the lumens of these membranes. Pure water permeability before and after bovine blood perfusion was measured using dead-end filtration. The scanning probe microscopy system was used for analysis. High-resolution three-dimensional pore structures on the inner surface of the membranes were observed before blood contact. On the other hand, many pore structures after blood contact could not be observed due to protein fouling. The pore diameters calculated by the tortuous pore diffusion model and scanning probe microscopy were mostly similar and could be validated reciprocally. Achievable pure water permeabilities showed no difference, despite protein fouling on the pore inlets (membrane surface). In addition, low values of albumin sieving coefficient are attributable to protein fouling that occurs on the membrane surface. Therefore, it is essential to design the membrane structure that provides the appropriate control of fouling. The characteristics of the hemoconcentration membranes examined in this study are suitable for clinical use.

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 examined typical commercial poly(ethersulfone) (PESf) hemodialysis and hemoconcentration membranes successfully used in manufacturing, and employed scanning probe microscope (SPM) to achieve a structural observation of the pores in the inner membrane surfaces, as well as measure the pore diameters and their distribution, verifying the relationship between the typical mass transfer properties. We focused on the differences between the PESf membranes which were expected to further improve the advanced pore structure control and functional design for various medical uses. The three-dimensional tortuous capillary pores on the inner surface of hollow fiber hemodialysis and hemoconcentrator membranes were investigated using dynamic force microscopy (DFM), and the pore diameter and distribution were measured through a line analysis. Compared with PUREMA-A, PES-Sα hemodialysis membranes have smaller three-dimensional tortuous capillary pore diameters and pore areas, as well as a smaller pore diameter distribution and pore area distribution, which make the accurate measurements of the pore diameter using FE-SEM impossible. These PESf membranes are almost the same in pure water permeability, but greatly differ in pore diameter and pore diameter distribution. By comparing and verifying as above, we may gain insight into the flexibility, versatility, and superior structural and functional controllability of PESf membrane pore structures, which could advance the development of pore structure control. Pending issues include the fact that, using a line analysis software of SPM devices, it is very difficult to measure hundred pores which clearly reflects the poor quality of pore size distributions obtained in this study, measurement accuracy must be improved further.