Polypyridyl Ru(II)-sensitizers with extended π-system enhances the performance of dye sensitized solar cells

New polypyridyl ruthenium(II) complexes “cis-Ru(4,4′-dimesityl-2,2′-bipyridine) (Ln) (NCS)₂ H102” and “cis-Ru(4,4′-bis(2,3,6-tri-isopropylphenyl)-2,2′-bipyridine) (Ln) (NCS)₂ H105”, where Ln = 4,4′-dicarboxylic acid-2,2′-bipyridine; were synthesized and successfully applied to sensitization of nano-crystalline TiO₂ based solar cells (DSSCs). The DSSCs of H102 and H105 fabricated from 0.16 cm² TiO₂ electrodes exhibited broader comparable photocurrent action spectra with almost identical solar-to-electrical energy conversion efficiency (η) as compared to N719 sensitizer. The incident photon-to-current conversion efficiency (IPCE) values of 98% and 95% were obtained for H102 and H105 sensitizers respectively. Under 1 sun condition, η-values of 8.39% (short-circuit photocurrent (J_SC) = 16.4 mA/cm², open-circuit photo voltage (V_OC) = 692 mV, fill factor = 0.734), 8.76% (J_SC = 16.3 mA/cm², V_OC = 735 mV, fill factor = 0.734) and 9.12% (J_SC = 16.1 mA/cm², V_OC = 745 mV, fill factor = 0.753) were obtained for H102, H105 and N719 sensitizers respectively.     

Synthesis and characterization of low-bandgap copolymers based on dihexyl-2H-benzimidazole and terthiophene

A series of new semiconducting polymers with 3-(hexyloxy)thiophene, 2,2-dihexyl-2H-benzimidazole (HBI) and thiophene units was synthesized using Stille polymerization. These random copolymers show good solubility at room temperature in organic solvents owing to the long alkyl chain in new acceptor, 2,2-dihexyl-2H-benzimidazole. In HBI, the sulfur at 2-position of 2,1,3-benzothiadiazole (BT) unit was replaced with the carbon to make a highly soluble electron deficient moiety while keeping the 1,2-quinoid form of BT unit. The spectra of the solid films show absorption bands with maximum peaks at about 408–526 nm and the absorption onsets at 550–692 nm, corresponding to band gaps of 1.79–2.25 eV. The onset wavelengths of the absorption spectra in thin films exhibit a gradual red-shift with decreased amount of dihexyl-2H-benzimidazol unit, that is, from 550 nm with PHOTDTHBI-9 to 692 nm with PHOTDTHBI-1. Under white light illumination (AM 1.5 G, 100 mW/cm²), the device with PHOTDTHBI-3:PCBM blend demonstrated a V_OC value of 0.36 V, a J_SC value of 1.20 mA/cm², and a FF of 0.37, leading to the efficiency of 0.16%.     

Crystal structures and magnetic properties of two molecular solids based on bis(maleonitriledithiolate)nickelate monoanion with substituted piperidinium cations

Two new molecular solids, [1-NaMePid][Ni(mnt)₂] (1) and [2-NaMePid][Ni(mnt)₂] (2) (mnt^2? = maleonitriledithiolate, [1-NaMePid]⁺ = 1-(1′-naphthylmethyl)piperidinium and [2-NaMePid]⁺ = 1-(2′-naphthylmethyl)piperidinium) have been characterized structurally and magnetically. Both [Ni(mnt)₂]^? anions and the cations of 1 and 2 form segregated column stacks, and the Ni(III) ions form a 1D zigzig alternating magnetic chain within a [Ni(mnt)₂]^? column through Ni···S, S···S, Ni···Ni, or π···π interactions. Some conformational features in two isomeric cations and the geometry of the individual [Ni(mnt)₂]^? anion for 1 and 2 remain similar, while the changes of the space filling properties, the packing requirements and the existence of the water molecule in 2 result in the difference of the stacking mode of the [Ni(mnt)₂]^? anions. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 is diamagnetism, while 2 exhibits a novel and interesting spin–gap transition around 16.8 K with antiferromagnetic interaction (J = ?4.6 cm^?1) in the high-temperature phase (HT) and the spin–gap (Δ/k_b = 68.5 K) in the low-temperature phase (LT).     

A blue organic emitting diode derived from new styrylamine type dopant materials

We have designed and synthesized new dopant materials based on the styrylamine moiety, 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]biphenyl (4) and 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]terphenyl (8). Blue OLEDs were obtained from new styrylamine dopant materials and compared with those of blue dopant bis[4-(di-p-N,N-diphenylamino)styryl]stilbene (DSA-Ph) and diphenyl[4-(2-terphenyl vinyl)phenyl]amine (R-BD). The ITO/DNTPD/NPB/MADN:dopant/Alq₃/Al-LiF device obtained from 4 shows blue EL spectrum at 469 nm and high efficiency 3.02 cd/A at 7 V. 8 also shows blue EL spectrum around λ_max = 468 nm, efficiency of 3.51 cd/A and a current density of 25.94 mA/cm² (855.7 cd/m²) at 7 V.     

Blue organic light-emitting materials based on diphenylaminofluorene and N-phenylcarbazole derivatives

A series of diphenylaminofluorene- and phenylcarbazole-derived, blue fluorescent molecules have been synthesized via the Hornor–Wadsworth–Emmons and Suzuki-cross coupling reactions. To explore the electroluminescent properties of these molecules, multilayer devices were fabricated with a structure of ITO/NPB/(1–6) doped in MADN/Bphen/Liq/Al, yielding a device that exhibited highly efficient sky-blue emissions with the luminous efficiency of 11.2 cd/A at 20 mA/cm², a power efficiency of 7.35 lm/W at 20 mA/cm², and CIE_x,y coordinates of (x = 0.16, y = 0.26) at 8 V. Also, a deep blue OLED with CIE_x,y coordinates of (x = 0.16, y = 0.13) at 8 V showed a luminous efficiency of 2.13 cd/A and power efficiency of 1.20 lm/W at 20 mA/cm², respectively.     

Doped and non-doped organic light-emitting diodes based on a yellow carbazole emitter into a blue-emitting matrix

A new carbazole derivative with a 3,3′-bicarbazyl core 6,6′-substituted by dicyanovinylene groups (6,6′-bis(1-(2,2′-dicyano)vinyl)-N,N′-dioctyl-3,3′-bicarbazyl; named (OcCz2CN)₂, was synthesized by carbonyl-methylene Knovenagel condensation, characterized and used as a component of multilayer organic light-emitting diodes (OLEDs). Due to its π-donor–acceptor type structure, (OcCz2CN)₂ was found to emit a yellow light at λ_max = 590 nm (with the CIE coordinates x = 0.51; y = 0.47) and was used either as a dopant or as an ultrathin layer in a blue-emitting matrix of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi). DPVBi (OcCz2CN)₂-doped structure exhibited, at doping ratio of 1.4 weight %, a yellowish–green light with the CIE coordinates (x = 0.31; y = 0.51), an electroluminescence efficiency η_EL = 1.3 cd/A, an external quantum efficiency η_ext = 0.4 % and a luminance L = 127 cd/m² (at 10 mA/cm²) whereas for non-doped devices utilizing the carbazolic fluorophore as a thin neat layer, a warm white with CIE coordinates (x = 0.40; y = 0.43), η_EL = 2.0 cd/A, η_ext = 0.7%, L = 197 cd/m² (at 10 mA/cm²) and a color rendering index (CRI) of 74, were obtained. Electroluminescence performances of both the doped and non-doped devices were compared with those obtained with 5,6,11,12-tetraphenylnaphtacene (rubrene) taken as a reference of highly efficient yellow emitter.     

Synthesis and photovoltaic application of donor–acceptor type copolymers containing 9-cyanomethylenefluorene derivatives with chemically tunable electronic properties

Four 9-cyanomethylenefluorene derivatives were synthesized as a new class of electron-deficient building blocks for donor–acceptor (D–A) type alternating copolymers. UV–vis absorption spectroscopy, cyclic voltammetry and density functional theory calculations show that the substituent X at the cyanomethylene unit, depending on its electron-withdrawing ability (X = –H, –CONMe₂, –COOiBu and –CN), can continuously control the LUMO energy level of the monomer. D–A type copolymers were synthesized using the derivatives and an oligothiophene as the electron-donating block. The photovoltaic performance of D–A copolymer:PCBM bulk heterojunction devices shows the importance of LUMO level alignment to achieve efficient charge separation at the donor/acceptor interface. After optimization, the power conversion efficiency of the device with X = –H reached 1.14% with V_OC of 0.61 V, J_SC of 3.24 mA cm^?2 and FF of 0.58 under the irradiation of AM1.5 simulated solar light. The electronic properties of the copolymers correlated well with the electron-withdrawing ability of the monomers while the structure of the π-conjugated backbone was preserved, demonstrating the advantage of the chemically tunable monomer design.     

Synthesis and characterization of poly[(R)-(−) and (S)-(+)-3-(1′-pyrrolyl)propyl-N-(3″,5″-dinitrobenzoyl)-α-phenylglycinate]s as chiral oligomers of pyrrole

Chiral polypyrrole oligomers were prepared from (R)-(?) (1) and (S)-(+)-3-(1′-pyrrolyl)propyl-N-(3″,5″-dinitrobenzoyl)-α-phenylglycinate (2) by oxidative polymerization in the presence of FeCl₃ as an oxidant. The new polymers were characterized by ¹H NMR, FTIR and UV–vis (λ_máx = 251 nm). TGA analyses of the corresponding polymers, poly1 and poly2, demonstrate an excellent thermal stability up to 204 °C, followed by two consecutive weight losses at higher temperatures. Relative number-average molecular weights of about 1.4 × 10³ and 2.3 × 10³, for poly1 and poly2, respectively, were measured by SEC, corresponding to oligomeric chains. Specific optical rotation measurements (c 0.1, THF) for poly1 [α]_D²⁰ = ?44 and poly2 ([α]_D²⁰ = +44) suggest that chirality is retained during the polymerization. Transversal section analysis of SEM images indicates the materials isolated right after the synthesis is highly porous.     

A cyclopentadithiophene/thienopyrroledione-based donor–acceptor copolymer for organic solar cells

A new cyclopentadithiophene/thienopyrroledione-based donor–acceptor copolymer (P1) was synthesized using a microwave-assisted Stille coupling procedure and was compared to a known benzodithiophene-based copolymer using the same thienopyrroledione acceptor monomer (PBDTTPD). Cyclopentadithiophene-based copolymers have been known to exhibit lower band gaps than their corresponding benzodithiophene-based counterparts. The polymer showed excellent solubility at room temperature in chlorinated solvents. The absorption onset for P1 is close to 740 nm as compared with ～685 nm for PBDTTPD, corresponding to an optical band gap of 1.67 eV, which is 0.15 eV lower than PBDTTPD. The photovoltaic characteristics of the polymer were determined under AM1.5 illumination. The P1:PCBM BHJ device showed a high V_oc (0.92 V) and J_sc (8.02 mA/cm²) as well as a good PCE (2.43%), while the best device with 2% solvent additive gave a PCE of 3.47%.     

Synthesis,characterization and nonlinear optical properties of 2-[(E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substitutedbenzenesulfonate compounds

In the present investigation, 2-[(E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substituted benzenesulfonate (X = CH₃ (1), X = OCH₃ (2), X = Cl (3), X = Br (4)) have been synthesized and characterized by ¹H NMR, UV–Vis and FT-IR spectroscopy methods. In addition compound 3 was also characterized by single crystal X-ray diffraction (XRD) and found that it crystallized out in the monoclinic space group P2₁ with cell parameters, a = 9.8072(9) Å, b = 6.4848(5) Å, c = 19.4405(16) Å, α = 90°, β = 103.421(5)°, γ = 90°, z = 2 and V = 1202.61(17) Å³. The nonlinear optical absorption of the samples has been studied at 532 nm using 5 ns laser pulses, employing the open-aperture z-scan technique. It is found that some of the samples are potential candidates for optical limiting applications.     

Highly efficient red electroluminescence induced by efficient electron injection and exciton confinement

Highly efficient DCJTB-doped device was realized by enhanced electron injection and exciton confinement. A fluorine end-capped linear phenylene/oxadiazole oligomer 2,5-bis(4-fluorobiphenyl-4′-yl)-1,3,4-oxadiazole (1) and a trifluoromethyl end-capped oligomer 2,5-bis(4-trifluoromethylbiphenyl-4′-yl)-1,3,4-oxadiazole (2) were designed and incorporated as an electron transporting/hole blocking material in the device structure ITO/NPB (60 nm)/DCJTB:Alq₃ (0.5%, 10 nm)/1 or 2 (20 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm). The devices showed highly efficient red luminescence. In particular, the device based on 1 achieved pure red luminescence at 620 nm originating from DCJTB, with a narrow FWHI of 65 nm, maximal brightness of 13,300 cd/m² at voltage of 20.8 V and current density of ca. 355 mA/cm². High current and power efficiencies (>3.6 cd/A, 1.0 lm/W) were retained within a wide range of current densities. Our results show efficient and stable DCJTB-doped red electroluminescence could be anticipated for practical applications by taking advantage of the present approaches. The control experiments using BCP were also studied.     

New amorphous electron-transporting materials based on Tris-benzimidazoles for all wet-process OLED devices

New amorphous electron-transporting materials 1,3,5-tris[1-(phenoxy phenyl)-1H-benzimidazol-2-yl]benzene (6a and 6b) were synthesized by dehydration reaction of corresponding triamides and fully characterized. Compounds 6a and 6b showed high thermal stability (T_g = 108 to 110 °C) and good solubility in common organic solvents, such as acetone, 2-methoxyetanol, tetrahydrofuran, chloroform, and 2-butanone. Pinhole-free transparent films were obtained by spin-casting the 2-butanone solution. 6a and 6b were fabricated as electron-transporting layer by spin-casting on a hole-transporting layer that was deposited by spin-cast beforehand and was insoluble in 2-butanone. Both devices showed no emission, but carrier transporting property was observed (400 mA/cm²). The device showed a blue emission (35 cd/m²) from 9,10-diphenylanthracene (DPA) when 10 wt.% DPA was mixed into the 6b layer.     

Metal ion sensing functional mono and double-decker lanthanide phthalocyanines: Synthesis,characterization and electrical properties

We report, in this study, the preparation, physical characterization metal ion sensing properties of peripherally functionalized ionophore ligand, 4,5-bis(6-hydroxyhexylthio)-1,2-dicyanobenzene (1) and its mono 2,3,7,8,12,13,17,18-octakis(6-hydroxyhexylthio)phthalocyaninatometal (II) {M = Zn^II (2), Cu^II (3)} and double-decker lanthanide bis-phthalocyanines, {([4,5,4′,5′ 4″,5″,4?,5?]-tetrakis-(6-hydroxyhexylthio)phthalocyaninatolanthanium(III)}){M[Pc(S–C₆H₁₃OH)₄]₂} {M = Eu^III (4), Yb^III (5), and Lu^III (6)}. All benzenes on phthalocyanines are functionalized with hydroxyhexylsulfanyl moieties for potential use as soft metal ion binding, such as Ag⁺ and Pd²⁺. The temperature dependence of the dc and ac conduction properties of 4, 5 and 6 thin films have been investigated in the frequency range of 40–10⁵ Hz and temperature range 290–436 K. The dc results showed an activated conductivity dependence on temperature for all films. Obtained data reveal that ac conductivity obeys the relation σ_ac(ω) = Aω^s and exponent is found to decrease by increasing temperature. The data obtained results were compared with the prediction of the Quantum Mechanical Tunelling (QMT) and Correlated Barrier Hopping (CBH) models. The analysis showed that the CBH model is the dominant conduction mechanism for the electron transport in the films. The new synthesized compounds have been characterized by elemental analysis, FTIR, ¹H and ¹³C NMR, MS, UV–vis and EPR spectral data.     

5′-(Anthracene-9,10-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene) derivatives bearing 5-ethynyl-5′-hexyl-2,2′-bithiophene and 2-ethynyl-5-hexylthieno[3,2-b]thiophene: Thin film transistors and photovoltaic applications

Novel 5,5′-(anthracene-9,10-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene)-based conjugated molecules have been synthesized via the Sonogashira coupling reaction. Newly synthesized anthracene-based molecules exhibit good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the two molecules were evaluated in organic thin film transistors (OTFTs). The two π-conjugated molecules 4 and 7 exhibit fairly high charge carrier mobilities—as high as 0.010–0.022 cm² V^?1 s^?1 (I_on/I_off > 10³)—without any annealing process. The high charge carrier mobilities of the as-spun films are attributed to the fact that the molecules demonstrated pronounced J-aggregation behavior, resulting in easy crystallization and dense coverage of the surface of a dielectric layer. In addition, two molecules were employed to fabricate organic photovoltaic (OPV) cells with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PC₆₁BM) without thermal annealing. As a result, the photovoltaic cell containing 7 had the best preliminary results with an open-circuit voltage of 0.92 V, a short-circuit current density of 1.82 mA/cm², and a fill factor of 0.32, offering an overall power conversion efficiency (PCE) of 0.54%.     

Synthesis,spectroscopy and electroluminescence of cadmium(II) polypyridyl complexes

Five new complexes [Cd(ptpy-R)₂](PF₆)₂ (ptpy = 4′-phenyl-2,2′:6′,2″-terpyridine; R = tert-Butyl (1), hexyloxy (2), carbozole-9-yl (3), naphthalene-1-yl-phenylamine-N-yl (4) and diphenylamine-N-yl (5)) were synthesized and characterized by ¹H NMR, elemental analyses, UV–vis spectroscopy and cyclic voltammetry. The emission color of resultant complex molecules has been tuned effectively, from violet (397 nm) for 1 to orange (602 nm) for 5 in film, by modifying the electron-donating ability of the substituent R. The UV–vis spectroscopy and the solution-state luminescence showing remarkable solvatochromism suggests the emission involves the intra-ligand charge transfer (¹ILCT) excited state, occurring from the substituent R moiety to Cd(II) coordinated terpyridine. The electroluminescence (EL) properties for these organic materials were also studied and complexes 3, 4 and 5 exhibit EL wavelength at 548 nm, 596 nm and 604 nm with maximum current efficiency of 3.25 cd/A, 3.15 cd/A and 2.16 cd/A, respectively.     

s-Triazine as an exchange linker in organic high-spin molecules

s-Triazine was used as an exchange linker to couple phenyl-t-butylnitroxide and t-butylated phenoxyl radicals. Quartet and triplet state systems of both types were identified by ESR spectroscopy. The quartet state zero field splittings of 2,4,6-tris(4-N-t-butyl-N-aminoxylphenyl)-s-triazine (1) and 2,4,6-tris(3,5-di-t-butyl-4-oxyphenyl)-s-triazine (2) were |D|=12 and 33 G, respectively. The phenoxyl-based systems were persistent in solution, but not solid state stable. The s-triazine unit accommodates planarity of attached phenyl rings in the solid state, as shown by crystallographic studies of 1 and phenolic precursors to the phenoxyl-based systems. Triradical (1) was subjected to magnetic analysis by an equilateral triangular model with mean field inter-radical interactions, giving J_intra/k_B=+9.0 K and J_inter/k_B=−1.45 K. A similar isosceles triangle model gave J_1-intra/k_B=+10.5 K, J_2-intra/J_1-intra=0.77 and J_inter/k_B=−1.3 K. Compound 1 thus has a ferromagnetically coupled quartet ground state, with a small AFM coupling between molecules.     

One-dimensional antiferromagnetic behavior of a chiral molecular crystal, α′-(S,S-DMBEDT-TTF)2PF6

The synthesis, crystal and electronic structures, resistivity, magnetic susceptibility, and dielectric constant of the novel chiral crystal, α′-(S,S-DMBEDT-TTF)₂PF₆ [DMBEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene] are presented. The α′-type donor arrangement affords the one-dimensional antiferromagnetic behavior with J = ?40 K. The calculated band structure indicates the pseudo-one-dimensional interaction in the molecular side-by-side direction along the b-axis. The frequency-dependent dielectric constant suggests the charge disproportionation above 100 K. The non-centrosymmetric space group due to the composed chiral molecules affords the possibility of piezoelectricity.     

Synthesis and characterization of dithienothiophene vinylene based co-polymer for bulk heterojunction photovoltaic cells

An electron-donor–acceptor type co-polymer, PDTTBBO, composed of 3,5-dihexyldithieno [3,2-b:2′3′-d] dithiophene as donor and 2,6-dimethyl benzo[1,2-d; 5,4-d′] bisoxazole as an acceptor unit was synthesized by Horner–Wadsworth–Emmons (HWE) olefination reaction via multi-step procedure. The UV–vis absorption and photoluminescence emission peaks of the co-polymer in chlorobenzene were observed in a range from UV to near 700 nm. The lowest unoccupied molecular orbital (LUMO) and highest unoccupied molecular orbital (HOMO) levels of the co-polymer were estimated at ?5.71 eV and ?3.46 eV, respectively, corresponding to a band-gap of 2.25 eV. Bulk heterojunction photovoltaic cells were fabricated using a blend of PDTTBBO and PCBM with a ratio of 1:1. The short-circuit current density (J_sc), open-circuit voltage (V_oc) and fill factor (FF) of the device were estimated to be 1.306 mA/cm², 0.628 and 0.37, respectively, corresponding to power conversion efficiency (PCE) of 0.31% under AM 1.5 illumination.     

Synthesis and photovoltaic properties of oligothiophene derivatives

In order to develop novel photovoltaic materials, 5-formyl-2,2′:5′,2″-terthiophene (3T-CHO) and rare earth (terbium) complex based on the 5,5′-bis(5-(2,2′-bithiophene))-2,2′-bipyridine (B2TBPY) ligand, were synthesized. The photovoltaic properties of 3T-CHO and Tb complex based on B2TBPY ligand were studied. Under 78.2 mW/cm² illumination, the ITO/3T-CHO/PCH/Al device has a short circuit current of 1.81 mA/cm², an open circuit voltage of 2.25 V, fill fact of 48.3% and photoelectric conversion efficiency of 2.52%. The ITO/B2TBPY-Tb/PCH/Al device has a short circuit current of 2.47 mA/cm², an open circuit voltage of 0.57 V, fill fact of 29.1% and photoelectric conversion efficiency of 0.52%.     

Sharp and red “single-chain” luminescence from poly[2,5-dialkoxy-1,4-phenylene vinylene] locked in ordered host matrix

We found that the luminescence profile of poly[2,5-di(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (OC₁₀C₁₀-PPV), which originally is an orange-emitting polymer, can red-shift significantly by ca. 30 nm (λ_max: from 585 to 614 nm) and become very narrow (full width at half maximum: 30 nm) when doped into poly{2-[m-(3′,7′-dimethyloctyloxy)phenyl]-1,4-phenylene vinylene} (m-Ph-PPV). Due to the ordered structure of the host polymer, the effective conjugation length of the guest polymer is extended as if the chains were frozen. Surprisingly, the OC₁₀C₁₀-PPV chains can even be more tightly locked in the ordered m-Ph-PPV matrix than in the cooled neat OC₁₀C₁₀-PPV film at 5 K.