Visible-to-ultraviolet (<340 nm) photon upconversion by triplet-triplet annihilation in solvents.

In this article, visible-to-ultraviolet photon upconversion (UV-UC) by triplet-triplet annihilation in the emission range shorter than 340 nm, which has not been explored well, is presented and the relevant physicochemical characteristics are elucidated. Investigations were carried out in several deaerated solvents using acridone and naphthalene derivatives as a sensitizer and emitter, respectively. Both upconversion quantum efficiency and sample photostability under continuous photoirradiation strongly depended on the solvent. The former dependence is governed by the solvent polarity, which affects the triplet energy level matching between the sensitizer and emitter because of the solvatochromism of the sensitizer. To elucidate the latter, first we investigated the photodegradation of samples without the emitter, which revealed that the sensitizer degradation rate is correlated with the difference between the frontier orbital energy levels of the sensitizer and solvent. Inclusion of the emitter effectively suppressed the degradation of the sensitizer, which is ascribed to fast quenching of the triplet sensitizer by the emitter and justifies the use of ketonic sensitizers for UV-UC in solvents. A theoretical model was developed to acquire insight into the observed temporal decays of the upconverted emission intensity under continuous photoirradiation. The theoretical curves generated by this model fitted the experimental decay curves well, which allowed the reaction rate between the emitter and solvent to be obtained. This rate was also correlated with the difference between the frontier orbital energy levels of the emitter and solvent. Finally, based on the acquired findings, general design guidelines for developing UV-UC samples were proposed.

Transparent and Nonflammable Ionogel Photon Upconverters and Their Solute Transport Properties.

Photon upconversion based on triplet-triplet annihilation (TTA-UC) is a technology to convert presently wasted sub-bandgap photons to usable higher-energy photons. In this paper, ionogel TTA-UC samples are first developed by gelatinizing ionic liquids containing triplet-sensitizing and light-emitting molecules using an ionic gelator, resulting in transparent and nonflammable ionogel photon upconverters. The photophysical properties of the ionogel samples are then investigated, and the results suggest that the effect of gelation on the diffusion of the solutes is negligibly small. To further examine this suggestion and acquire fundamental insight into the solute transport properties of the samples, the diffusion of charge-neutral solute species over much longer distances than microscopic interpolymer distances is measured by electrochemical potential-step chronoamperometry. The results reveal that the diffusion of solute species is not affected by gelation within the tested gelator concentration range, supporting our interpretation of the initial results of the photophysical investigations. Overall, our results show that the advantage of nonfluidity can be imparted to ionic-liquid-based photon upconverters without sacrificing molecular diffusion, optical transparency, and nonflammability.

Isomerically pure anthra[2,3-b:6,7-b']-difuran (anti-ADF), -dithiophene (anti-ADT), and -diselenophene (anti-ADS): selective synthesis, electronic structures, and application to organic field-effect transistors.

A new straightforward synthesis of isomerically pure anthra[2,3-b:6,7-b'] -difuran (anti-ADF), -dithiophene (anti-ADT), and -diselenophene (anti-ADS) from readily available 2,6-dimethoxyanthracene is described. The present successful synthesis makes it possible to overview the linear-shaped anti-acenedichalcogenophene compounds, that is, benzo[1,2-b:4,5-b']-, naphtho[2,3-b:6,7-b']-, and anthra[2,3-b:6,7-b']- difuran, -dithiophene, and -diselenophene. By comparing their electrochemical and photochemical properties, the electronic structures of acenedichalcogenophenes can be expressed as the outcome of balance between the central acene core and the outermost chalcogenophene rings. Among isomerically pure parent anti-anthradichalcogenophenes, anti-ADT and anti-ADS can afford crystalline thin films by vapor deposition, which acted as active layer in organic field-effect transistors with mobility as high as 0.3 cm(2) V(-1) s(-1) for ADT and 0.7 cm(2) V(-1) s(-1) for ADS. The mobility of isomerically pure anti-ADT is higher by several times than those reported for isomercally mixed ADT, implying that the isomeric purity could be beneficial for realizing the better FET mobility. We also tested the diphenyl derivatives of anti-ADF, -ADT, and -ADS as the active material for OFET devices, which showed high mobility of up to 1.3 cm(2) V(-1) s(-1).

[2,2']Bi[naphtho[2,3-b]furanyl]: a versatile organic semiconductor with a furan-furan junction.

[2,2']Bi[naphtho[2,3-b]furanyl] was synthesized, characterized, and examined as an organic semiconductor for thin-film OFETs, bilayer OPVs, and organic light-emitting transistors (OLETs). In the devices, the material acted as a p-type semiconductor, showing moderately high mobility in OFETs, good photo conversion efficiency in OPVs, and blue-green emission in OLETs.

General synthesis of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) derivatives.

A new straightforward synthesis of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) derivatives from readily available 2-methoxynaphthalenes is described. Thus, newly developed derivatives of DNTT showed very high field effect mobility in the vapor-processed field-effect transistors up to 8 cm(2) V(-1) s(-1).

Dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT): synthesis, characterization, and FET characteristics of new π-extended heteroarene with eight fused aromatic rings.

A novel highly π-extended heteroarene with eight fused aromatic rings, dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT), was selectively synthesized via a newly developed synthetic strategy, fully characterized by means of single crystal X-ray structural analysis, and examined as an organic semiconductor in thin film transistors. Even with its highly extended acene-like π-system, DATT is a fairly air-stable compound with IP of 5.1 eV. Single crystal X-ray structural analysis revealed its planar molecular structure and the lamella-like layered structure with typical herringbone packing. Theoretical calculations of the solid state electronic structure based on the bulk single crystal structure suggest that DATT affords almost comparable intermolecular orbital couplings between HOMOs (t(HOMO)) with those of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), implying its good potential as an organic semiconductor for organic field-effect transistors. In fact, field-effect mobilities as high as 3.0 cm(2) V(-1) s(-1) were achieved with vapor-processed DATT-based devices, which is comparable with that of DNTT-based devices. The molecular ordering of DATT in the thin film state, however, turned out to be not completely uniform; as elucidated by in-plane and out-of-plane XRD measurements, the face-on molecular orientation was contaminated in the edge-on orientation, the former of which is not optimal for efficient carrier transport and thus could limit the mobility.