Triplet-triplet annihilation photon upconversion from diphenylhexatriene and ring-substituted derivatives in solution.

We report that diphenylhexatriene (DPH) and its ring-substituted derivatives act as emitter molecules in triplet-triplet annihilation photon upconversion (TTA-UC). A palladium porphyrin derivative, -tetraphenyl-tetrabenzoporphine palladium complex (PdTPBP), which acts as a sensitiser in TTA-UC, and DPH derivatives were dissolved in tetrahydrofuran (THF). The solution showed blue-green to green UC emission under photoexcitation at 640 nm in a nitrogen atmosphere.

Oriented Thin Films of Insoluble Polythiophene Prepared by the Friction Transfer Technique.

A thin film of unsubstituted polythiophene (PT), an insoluble conjugated polymer, with molecular chains uniaxially oriented in plane was prepared by the friction transfer method. The structure of highly oriented thin films of PT was investigated using grazing-incidence X-ray diffraction (GIXD), ultraviolet-visible (UV-vis) spectroscopy, and infrared (IR) spectroscopy. The polarized UV-vis and IR spectra and GIXD measurements showed the PT molecular chains were well aligned in parallel to the friction direction.

Triplet-triplet annihilation upconversion through triplet energy transfer at a nanoporous solid-liquid interface.

We report the triplet-triplet annihilation (TTA) upconversion (UC) through triplet energy transfer (TET) from a sensitiser fixed on a solid surface to free emitters dissolved in solution. A carboxylic-acid derivative of Pt-porphyrin was used as the sensitiser fixed on an amino-treated surface of continuous nanoporous glass without aggregation. UC emission was observed under photoexcitation of 532 nm for porphyrin-fixed glass immersed in an emitter solution of 9,10-diphenylanthracene (DPA), showing that TET occurs through the solid-liquid interface.

Synergetic Effects of Triplet-Triplet Annihilation and Directional Triplet Exciton Migration in Organic Crystals for Photon Upconversion.

In condensed solids, triplet exciton migration and succeeding triplet-triplet annihilation (TTA) are major bottleneck processes for efficient photon upconversion (UC) using sunlight excitation. We theoretically investigated the reaction times of TTA and the triplet-triplet energy transfer (TTET) as the elementary processes of triplet exciton migration in organic crystals of two molecular species: 9,10-diphenylanthracene (DPA) and its double-strapped alkyl  derivative (C7-sDPA) as the models of a recently reported crystalline system of TTA-UC by Kamada et al. The reaction times calculated based on Marcus theory clarified that the dimensionality of TTET and synergetic effects of TTA and TTET are responsible for the high UC quantum yield as well as their triplet lifetimes.

Enhanced phosphorescence properties of a Pt-porphyrin derivative fixed on the surface of nano-porous glass.

The room-temperature phosphorescence chromophore, Pt(ii) coproporphyrin I (PtCP), was fixed on the surface of a 3D-network of nanoscale pores of porous glass through ion-exchange reaction. The absorption and phosphorescence spectra indicated that PtCP can be loaded while maintaining monomeric dispersion at concentrations well beyond solubility limits of PtCP in solution. The phosphorescence quantum yield of PtCP fixed on the surface was also found to have double the enhancement of solution.

Organic Photovoltaic Devices Based on Oriented -Type Molecular Films Deposited on Oriented Polythiophene Films.

The molecular orientation of π-conjugated molecules has been reported to significantly affect the performance of organic photovoltaic devices (OPVs) based on molecular films. Hence, the control of molecular orientation is a key issue toward the improvement of OPV performance. In this research, oriented thin films of an n-type molecule, 3,4,9,10-Perylenetetracarboxylic Bisbenzimida-zole (PTCBI), were formed by deposition on in-plane oriented polythiophene (PT) films.

Organic heterojunctions: Contact-induced molecular reorientation, interface states, and charge re-distribution.

We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure - in the presence of Fermi-level pinning - at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (EF) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes EF-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface.

Orientation of α-sexithiophene on friction-transferred polythiophene 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.