Polyalkylthiophene-containing electron donor and acceptor heteroaromatic bicycles: synthesis, photo-physical, and electroluminescent properties

The synthesis and characterization of a series of polyalkylthiophenes-containing electron-rich thienothiophene (donor heteroaromatic bicycle) and electron-deficient benzothiadiazole (acceptor heteroaromatic bicycle) block have been reported. The polymers are synthesized by Stille cross-coupling reaction and are found to be having high molecular weight with number-average molecular weight in the range of 7.1 x 10(4)-5.7 x 10(4). The photo-physical, electro-chemical, and electroluminescent (EL) properties of the polymers are investigated in detail. The optical band gap of the polymers is found to be in the range of 1.53-1.54 eV. These new polymers are luminescent in nature and showed red photoluminescence in chloroform solution (722-740 nm) as well as in thin film (781-786 nm). Ionization potential for these polymers is calculated and falling in the range of 5.23-5.33 eV. Polymer light emitting diodes with configuration ITO/PDOT:PSS/polymer/BCP/Alq(3)/LiF/Al have been fabricated, and a deep red emission is observed. The EL maxima of polymers are found to be in the range of 750-760 nm with threshold voltages around 4.0-5.5 V. The fabricated devices show luminescence around 40 cd/m(2) at current density of 100 mA/cm(2) with maximum value of 580-810 cd/m(2) at 11 V

Fluorene-based conjugated poly(arylene ethynylene)s containing heteroaromatic bicycles: preparation and electro-optical properties

A series of high molecular weight fluorene-based soluble poly(arylene ethynylene)s (PAEs) have been prepared and characterized. The polymers consist of 2,5-bis(3-tetradecylthiophen-2-yl)-3a,6a-dihydrothieno[3,2-b]thiophene, 2,5-bis(3-tetradecylthiophen-2-yl)-3a,6a-dihydrothiazolo[5,4-d]thiazole, or 4,7-bis(3-tetradecylthiophen-2-yl)benzo[c] [1, 2, 5] thiadiazole unit with an electron donor 9,9-bis(2-ethylhexyl)-9H-fluorene unit connected via electron accepting ethynylene linkage. The molecular weights (M (w)) of the polymers were found to be in the range of 103600-179000 g/mol with polydispersity index (PDI) of 3.9-5.0. Optical and redox properties have been investigated by UV-visible, fluorescence spectroscopy, and cyclic voltammetry (CV) measurements. Combination of experimental and density functional theory (DFT) calculations indicated that the benzothiadiazole unit incorporated polymer has lowest band gap with most stable lowest unoccupied molecular orbital (LUMO) energy level. Polymer light emitting diode properties have been investigated for the polymer having highest molecular weight with device configuration ITO/PEDOT:PSS/Polymer/LiF/Al. Well-behaved diode characteristics with EL maxima at 600 nm were observed

Polymer binder assisted, solution processed cyanophenyl functionalized diketopyrrolopyrrole microwire for n-channel field-effect transistors

A cyanophenyl functionalized diketopyrrolopyrrole molecular semiconductor, DPP-PhCN, is used as an nchannel active material for organic field-effect transistors (FETs) with a polymer gate dielectric. Two types of DPP-PhCN active layer are prepared for the formation of the FET devices; 1) thin-film formed through a thermal vacuum deposition at different substrate temperatures and 2) microwire (single and multiple), prepared through a polymer binder assisted solution process. Both types of devices show electron dominant charge transport behavior. The device based on the polymer assisted solution processed microwire exhibit higher performance than the device with a thin-film. The highest electron mobility of 0.23 cm(2)/Vs in ambient condition is achieved from a device with only one microwire of DPP-PhCN, and is 30 times higher than that of the device with DPP-PhCN thin-film (0.008 cm(2)/Vs)

Substituent effect on the optoelectronic properties of poly(p-phenylenevinylene) based conjugated-nonconjugated copolymers

Two classes of light emitting Poly(p-phenylenevinylene) (PPV) based conjugated-nonconjugated copolymers (CNCPs) have been synthesized. The conjugated chromophores containing 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEHPV) and 2,5-dimethyl-1,4-phenylenevinylene (DMPV) moieties are rigid segments and nonconjugated portion containing hexyl units are flexible in nature. All copolymers were synthesized by well-known Wittig reaction between the appropriate bisphosphonium salts and the dialdehyde monomers. The resulting polymers were found to be readily soluble in common organic solvents like chloroform, THF and chlorobenzene. The effect of chromophore substituents on the optical and redox properties of the copolymers has been investigated. Color tuning was carried out by varying the molar percentage of the comonomers. The UV-Vis absorption and PL emission of the copolymers were in the range 314–395 nm and 494–536 nm respectively. All the polymers show good thermal stability. Polymer light-emitting diodes (PLEDs) were fabricated in ITO/PEDOT:PSS/emitting polymer/cathode configurations of selected polymers using double-layer, LiF/Al cathode structure. The emission maxima of the polymers were around 499–536 nm, which is a blue-green part of the color spectrum. The threshold voltages of the EL polymers were in the range of 5.4–6.2 V

Dithieno[3,2-b:2′,3′-d]pyrrole–alkylthiophene–benzo[c][1,2,5]thiadiazole-based highly stable and low band gap polymers for polymer light-emitting diodes

A series of new low band gap π-conjugated polymers containing N-alkyldithieno[3,2-b:2′,3′-d]pyrrole, benzo[c][1,2,5]thiadiazole, and alkylthiophenes are reported. The polymerization condition was standardized and the use of CuO to obtain high-molecular-weight polymer was also realized. The molecular weight of the polymers was found to be in the range of 45,000–53,000. All the polymers were found to be soluble in most of the common organic solvents, such as chloroform, dichloromethane, THF, and chlorobenzene with excellent film forming properties. The λmax of the polymers was found to be in the range of 687–663 nm with band gap in the range of 1.35–1.43 eV. The oxidation potential of the polymers from cyclic voltammetry was determined to be 0.5–0.75 V. The HOMO levels of the above synthesized polymers were found to be between 5.24 and 5.54 eV. All the polymers exhibited a PL emission in between 755 and 773 nm. The polymers were found to be thermally stable above 277 °C with only a 5% weight loss. From the thermal stability values, it is expected that the current set of polymers are stable enough for the application in electronic devices. To realize the potential use of the polymers, EL devices were fabricated and found to show red emission with comparatively low threshold voltage. A brightness of 54 cd m−2 for the device with polymer PC could be reached

Synthesis and characterization of alternative donor–acceptor arranged poly(arylene ethynylene)s derived from 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP)

A series of donor–acceptor type poly(arylene ethynylene)s (PAEs) have been synthesized through Sonogashira polycondensation. The polymers consist of an electron donating 9,9-bis(2-ethylhexyl)-9H-fluorene, triphenylamine, 1,4-dialkoxybenzene or 9-(2-ethylhexyl)-9H-carbazole unit and an electron accepting 2,5-bis(2-ethylhexyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (EH-DPP) unit, alternately connected through ethynyl bridge. The polymers exhibit weight-average molecular weights (Mw) up to 68, 500 and are soluble in chlorobenzene, dichlorobenzene, THF, chloroform and toluene. A brilliant red solution with absorption maxima between 491 and 500 nm was observed for all the polymers. An intense red fluorescent with photoemission maxima between 551 and 571 nm was observed from polymer solutions. The polymers showed good thermal stability with decomposition temperature more than 260 °C at 5% weight loss. Onset oxidation potentials of the polymers were observed between 1.30 and 1.58 V with HOMO energy levels in the range of −6.10 to −6.38 eV. The OLED devices were fabricated with configuration of ITO/PEDOT:PSS/polymer/LiF/Al for all the polymers and EL maxima between 666 and 684 nm were observed

n-Type ternary zinc complexes: Synthesis, physicochemical properties and organic light emitting diodes application

We report synthesis, characterization and use of ternary zinc complexes as emissive and electron transport material in organic light emitting devices (OLED). 5,7-Dimethyl-8-hydroxyquinoline or 2-carbonitrile-8-hydroxyquinoline have been used with 2-(2-hydroxyphenyl)benzoxazole to synthesize (2-(2-hydroxyphenyl)benzoxazolato) (5,7-dimethyl-8-hydroxyquinolinato)zinc(II) [Zn(HPB)(Me(2)q)] and (2-(2-hydroxyphenyl) benzoxazolato)(2-carbonitrile-8-hydroxyquinolinato)zinc(II) [Zn(HPB)(CNq)] complexes. These complexes possessed high thermal stability and having good film forming property. Optical properties of the synthesized complexes have been studied by UV-visible absorption, photoluminescence and time resolved photo-luminescence spectroscopy. Density functional theoretical calculations have been performed to demonstrate the three-dimensional geometries and the frontier molecular orbital energy levels of these compounds. Synthesized materials show quite good efficiency in multilayered device structure ITO/alpha-NPD/Zinc complex/BCP/Alq(3)/LiF/Al with maximum brightness of 7017 cd/m(2) and 6925 cd/m(2) having electroluminescence spectral peak emission centered at 567 nm and 569 nm, respectively. Electron mobility of these molecules were found to be 1.5 x 10(-6)-1.2 x 10(-5) cm(2)/V s for electric field range 1000-1200 (V/cm)(1/2) and hence showed very high efficiency as electron transport layer in device structure ITO/alpha-NPD/5% Ir(ppy)(3) doped CBP/BCP/Zn(HPB)(Me(2)q) or Zn(HPB)(CNq)/LiF/Al

Solution-grown single-crystalline microwires of a molecular semiconductor with improved charge transport properties

Preparation and structural analysis of highly ordered single crystalline wires of a diketopyrrolopyrrole (DPP) molecular semiconductor grown through a solution process are reported, and the static/dynamic electrical response of an organic electronic device using the DPP semiconductor has been analyzed