Synthesis and characterization of an anthracene-based low band gap polymer for photovoltaic devices.

We have synthesized an anthracene-based conjugated polymer, poly[(9,10-bis(oct-1-ynyl)anthracene)-alt-(5,6-bis(octyloxy)-4,7-bis(thiophen-2-yl)benzo-[c][1,2,5]-thiadiazole)] (PANTBT), for application in organic photovoltaic devices. It exhibited a number average molecular weight of 14,300 g/mol and was fairly soluble in chlorinated organic solvents due to flexible octynyl- and octyloxy side chains on the anthracene and benzothiadiazole moieties. PANTBT showed absorption covering 300-660 nm. Through the bond alternation between the electron-sufficient anthracene (and thiophene) and electron-deficient benzothiadiazole units, a band gap of PANTBT was decreased to 1.89 eV, showing a deep HOMO level of -5.31 eV. As a result, PANTBT exhibited promising photovoltaic properties with a PCE value of 1.90% (VOC = 0.77 V, JSC = -6.50 mA/cm2, FF = 0.38) upon blending with PC71, BM under AM 1.5G.

Cationic conjugated polyelectrolytes-triggered conformational change of molecular beacon aptamer for highly sensitive and selective potassium ion detection.

We demonstrate highly sensitive and selective potassium ion detection against excess sodium ions in water, by modulating the interaction between the G-quadruplex-forming molecular beacon aptamer (MBA) and cationic conjugated polyelectrolyte (CPE). The K(+)-specific aptamer sequence in MBA is used as the molecular recognition element, and the high binding specificity of MBA for potassium ions offers selectivity against a range of metal ions. The hairpin-type MBA labeled with a fluorophore and quencher at both termini undergoes a conformational change (by complexation with CPEs) to either an open-chain form or a G-quadruplex in the absence or presence of K(+) ions. Conformational changes of MBA as well as fluorescence (of the fluorophore in MBA) quenching or amplification via fluorescence resonance energy transfer from CPEs provide clear signal turn-off and -on in the presence or absence of K(+). The detection limit of the K(+) assays is determined to be ~1.5 nM in the presence of 100 mM Na(+) ions, which is ~3 orders of magnitude lower than those reported previously. The successful detection of 5'-adenosine triphosphate (ATP) with the MBA containing an ATP-specific aptamer sequence is also demonstrated using the same sensor scheme. The scheme reported herein is applicable to the detection of other kinds of G-rich aptamer-binding chemicals and biomolecules.

Synthesis of new fluorene-based copolymers containing an anthracene derivative and their applications in polymeric light-emitting diodes.

We report the synthesis of copolymers containing fluorene and highly soluble anthracene derivatives, of general formula, poly{9,9'-bis-(4-octoloxy-phenyl)-fluorene-2,7-diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}s (PFAnts). The PFAnts were synthesized via Suzuki coupling and the feed ratios of the anthracene derivative (Ant) were 1, 5, 10, 30, and 50 mol % of the total amount of monomer. PFAnts showed well-defined high molecular weights and were more soluble in conventional organic solvents. The photoluminescence spectra of PFAnts shifted to longer wavelengths with increases in Ant proportion and the PFAnts emitted various colors varying from greenish-blue to orange. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels trended toward enhanced hole and electron recombination balance as the Ant proportion increased, due to the better electron-accepting ability of the anthracene moiety compared to the fluorene moiety. Polymeric light-emitting diodes with the configurations ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Ca(10 nm)/Al(100 nm) (Device A) and ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Balq(40 nm)/LiF(1 nm)/Al(100 nm) (Device B) were fabricated using the polymers as emissive layers. Especially, Device B with PFAnt01 exhibited the highest measured maximum brightness of 1760 cd/m2 at 14 V, a maximum current efficiency of 1.66 cd/A, and a maximum external quantum efficiency of 0.70%.

Synthesis and photovoltaic properties of cyclopentadithiophene-based low-bandgap copolymers that contain electron-withdrawing thiazole derivatives.

We have synthesized four types of cyclopentadithiophene (CDT)-based low-bandgap copolymers, poly[{4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl}-alt-(2,2'-bithiazole-5,5'-diyl)] (PehCDT-BT), poly[(4,4-dioctyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)-alt-(2,2'-bithiazole-5,5'-diyl)] (PocCDT-BT), poly[{4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5'-diyl}] (PehCDT-TZ), and poly[(4,4-dioctyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5'-diyl}] (PocCDT-TZ), for use in photovoltaic applications. The intramolecular charge-transfer interaction between the electron-sufficient CDT unit and electron-deficient bithiazole (BT) or thiazolothiazole (TZ) units in the polymeric backbone induced a low bandgap and broad absorption that covered 300 nm to 700-800 nm. The optical bandgap was measured to be around 1.9 eV for PehCDT-BT and PocCDT-BT, and around 1.8 eV for PehCDT-TZ and PocCDT-TZ. Gel permeation chromatography showed that number-average molecular weights ranged from 8000 to 14,000 g mol(-1). Field-effect mobility measurements showed hole mobility of 10(-6)-10(-4) cm(2) V(-1) s(-1) for the copolymers. The film morphology of the bulk heterojunction mixtures with [6,6]phenyl-C(61)-butyric acid methyl ester (PCBM) was also examined by atomic force microscopy before and after heat treatment. When the polymers were blended with PCBM, PehCDT-TZ exhibited the best performance with an open circuit voltage of 0.69 V, short-circuit current of 7.14 mA cm(-2), and power conversion efficiency of 2.23 % under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm(-2)).

Organic thin film transistors using a polyhedral oligomeric silsesquioxane-based photo-patternable insulating material.

We synthesized a new photo-patternable organic/inorganic hybrid material, polyhedral oligomeric silsesquioxane (POSS) derivative containing cyclohexene-1,2-epoxide functional groups (POSS-EPOXY), and fabricated an organic thin film transistor (OTFT) using pentacene as an active p-type organic semiconductor and POSS-EPOXY as a gate dielectric layer to demonstrate its applicability for organic electronics. The pentacene transistor with the POSS-EPOXY layer shows comparable transistor characteristics as that with the prototypical polymeric gate insulator of poly(vinylphenol) (PVP). They exhibit field-effect mobility of micro(FET) approximately 0.075 cm2/Vs, threshold voltage of V(T) = -22.2 V, the on/off current ratio of 7 x 10(5), and the subthreshold slope of 3.9 V/dec.

Synthesis and properties of a polyhedral oligomeric silsesquioxane-based new light-emitting nanoparticle.

A polyhedral oligomeric silsesquioxane (POSS)-based electroluminescent nanoparticle, POSS-NPA, which contains anthracenenaphthyl chromophores on each of its eight arms, was easily prepared via the hydrosilylation reaction between octakis(dimethylsiloxy)silsesquioxane and allyl-functionalized 9-naphthalene-2-yl-10-phenyl anthracene chromophores. POSS-NPA was completely soluble in common organic solvents such as chloroform, THF, toluene, p-xylene, and chlorobenzene, and showed good film-forming properties on a quartz plate or an indium tin oxide (ITO) plate, i.e., it has good solution processing properties. The UV-visible absorption and the photoluminescence (PL) emission maxima of POSS-NPA in chlorobenzene solution were found to be 378 nm and 433 nm while those of POSS-NPA in the solid state were 379 and 464 nm, respectively. An electroluminescent (EL) device with the configuration of ITO/PEDOT:PSS/POSS-NPA (50 nm)/BAIq (40 nm)/LiF (1 nm)/Al (120 nm) was also fabricated and the blue light emission was successfully obtained.

Enhanced emission and two-photon absorption cross-section by nanoaggregation of a cyano-substituted stilbene derivative.

This study reports the synthesis and the investigation of optical behaviors of a stilbene derivative, (Z)-2,3-bis[4-(N-4-(diphenylamino)styryl)phenyl]acrylonitrile (StCN). The nanoaggregates of StCN in 50% water/DMF have exhibit an increased fluorescence intensity and a blue shift with emission maximum wavelength with respect to StCN in 100% N, N-dimethylformamide (DMF) solution. This fluorescence enhancement can be attributed to the formation of J-aggregates. The cyano group prevents coplanarization of both arms and intermolecular face-to-face orientation leading to the formation of J-aggregates preventing the solvent relaxation. A strong fluorescence bathochromic solvatochromism is indicative of a large dipole moment in solution. Also, the two-photon absorption cross-section of nanoaggregates has been increased 1.5 times compared to that in DMF solution at the maximum wavelength.

Synthesis of a new polymeric host material for efficient organic electro-phosphorescent devices.

We have synthesized a new polymeric host material for phosphorescent dyes, which can be used in phosphorescent light-emitting layers. An alternating copolymer, composed of N-alkylcarbazole and tetramethylbenzene units was synthesized through the Suzuki coupling reaction. We fabricated electro-phosphorescent devices using the synthesized polymeric host doped with solution-processible green and red phosphorescent dyes. Light-emitting devices have an ITO/PEDOT/polymer + dopant/Balq3/Alq3/LiF/Al configuration. The device containing one of two studied green dopants (designated as green 1) in the polymeric host showed the best performance, with a maximum luminous efficiency of 29 cd/A. A thin film of this polymeric was successfully patterned by laser-induced thermal imaging (LITI), and an electro-phosphorescent device was fabricated using the patterned film. This patterned device showed performance characteristics similar to those of a spin-coated device.

Soluble and easily crystallized anthracene derivatives: precursors of solution-processable semiconducting molecules.

New soluble anthracene derivatives containing thiophene and phenylenevinylene derivatives were synthesized via well-known synthetic routes. TIPS derivatives were added at the 9,10-positions of anthracene for the solubility and crystallinity. Both of the molecules were found to be promising for high charge mobility and stable organic semiconductors. The soluble anthracene core (TIPSAnt) is a potential precursor for the synthesis of novel semiconducting materials.

Synthesis and characterization of a thiazolo[5,4-d]thiazole-based copolymer for high performance polymer solar cells.

A highly processable, new semiconducting polymer, PCDTTz, based on alternating thiazolothiazole and carbazole units was synthesized. The new polymer exhibited a field-effect carrier mobility of up to 3.8 × 10(-3) cm(2) V(-1) s(-1) and bulk heterojunction solar cells made from PCDTTz produced a power conversion efficiency of 4.88% under AM 1.5 G (100 mW cm(-2)) conditions.

New anthracene-thiophene-based copolymers that absorb across the entire UV-vis spectrum for application in organic solar cells.

We report a new class of anthracene-thiophene-based copolymers, PAT4. The UV-vis absorption spectrum of PAT4 was broad and covered the full range of the solar spectrum. The hole mobility of PAT4 was high, up to 0.037 cm(2) V(-1) s(-1). PAT4-based organic solar cells showed promising power conversion efficiencies of 1.7%.

A new amorphous semiconducting polythiophene for high-performance organic thin-film transistors.

A new amorphous semiconducting polymer containing dodecylthiophene rings and a rigid thieno[3,2-b]thiophene ring, poly(2,5-bis(3'-dodecyl-2,2'-bithiophen-5-yl)thieno[3,2-b]thiophene) (NAP), was synthesized via a microwave-assisted Stille coupling reaction. The presence of the flexible unsubstituted thiophene ring units next to the rigid fused thiophene ring caused NAP to have an amorphous structure. This structure was confirmed by XRD, AFM, and computational calculations. In particular, the out-of-plane XRD patterns of NAP thin films exhibited no reflection peaks before or after the annealing process, indicating that the films had amorphous microstructures. In addition, AFM images of the NAP thin films showed amorphous surface morphologies with very small root-mean-square (rms) surface roughnesses of 0.3-0.5 nm, independent of surface treatment or heat treatment. Computational calculations performed to investigate the preferred conformation of the polymer confirmed the amorphous characteristics of the NAP structure. On the basis of these findings, we propose how an amorphous NAP semiconductor can maintain high carrier mobility. A NAP-based TFT device exhibited a very high carrier mobility of 0.02 cm(2) V(-1) s(-1) with an on/off ratio of 1 x 10(5) and a very small threshold voltage of -2.0 V. This carrier mobility is the highest yet reported for TFTs based on amorphous semiconductors. Thus, the present findings suggest that an amorphous semiconductor layer comprised of NAP would be suitable for use in high-performance organic TFTs fabricated via simple processes in which neither surface treatment nor heat treatment is necessary.

Room temperature fabrication of ZnO nanorod films: synthesis and application as a channel layer of transparent thin film transistors.

We report a single-step, solution-based synthesis even at room temperature utilizing a facile sonochemical method to fabricate ZnO nanocrystalline films consisting of well-aligned nanorods.