Design of a Quinoidal Thieno[3,4‐b]thiophene‐Diketopyrrolopyrrole‐Based Small Molecule as n‐Type Semiconductor

A quinoidal small‐molecule semiconductor QDPPBTT was synthesized. Organic thin‐film transistor (OTFT) devices based on QDPPBTT showed an electron mobility as high as 0.13 cm² V^?1 s^?1 and I_on/I_off ratio of 10⁶ under ambient conditions. We suggested that 2D extended π‐conjugation and quinoid‐enhancing effect had an important role in electron mobility and stability of n‐type FET devices, which might be a good strategy in designing new material systems.     

A Fluorescent Chemosensor for Dihydrogen Phosphate Ion Based on 2‐[2‐Hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine‐Fe3+ Ensemble

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H₂PO₄^? ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe³⁺ ion, Fe³⁺ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY‐Fe³⁺ ensemble could recover the quenched fluorescence upon the addition of H₂PO₄^? anion resulting in an off‐on‐type sensing with a detection limit of micromolar range in the same medium, and other anions, including F^?, Cl^?, Br^?, I^?, AcO^?, HSO₄^?, ClO₄^? and CN^? had nearly no influence on the probing behavior. The test strips based on 2‐[2‐hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine and Fe³⁺ metal complex ( GY‐Fe³⁺ ) were fabricated, which could act as convenient and efficient H₂PO₄^? test kits.     

The Role of Ion Pairs in the Second‐Order NLO Response of 4‐X‐1‐Methylpiridinium Salts

A series of 4‐X‐1‐methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)‐CH?CHC₆H₅; (E)‐CH?CHC₆H₄‐4′‐C(CH₃)₃; (E)‐CH?CHC₆H₄‐4′‐N(CH₃)₂; (E)‐CH?CHC₆H₄‐4′‐N(C₄H₉)₂; (E,E)‐(CH?CH)₂C₆H₄‐4′‐N(CH₃)₂) with various organic (CF₃SO₃^?, p‐CH₃C₆H₄SO₃^?), inorganic (I^?, ClO₄^?, SCN^?, [Hg₂I₆]^2?) and organometallic (cis‐[Ir(CO)₂I₂]^?) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second‐order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second‐order NLO response, investigated by the electric‐field‐induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10^?3 M , and their dipole moments were determined. Generally, below 5×10^?4 M , ion pairs start to dissociate into ions with parallel increase of the second‐order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10^?3 M , some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second‐order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self‐aggregate.     

Dithienoindophenines: p‐Type Semiconductors Designed by Quinoid Stabilization for Solar‐Cell Applications

Compared with the dominant aromatic conjugated materials, photovoltaic applications of their quinoidal counterparts featuring rigid and planar molecular structures have long been unexplored despite their narrow optical bandgaps, large absorption coefficients, and excellent charge‐transport properties. The design and synthesis of dithienoindophenine derivatives (DTIPs) by stabilizing the quinoidal resonance of the parent indophenine framework is reported here. Compared with the ambipolar indophenine derivatives, DTIPs with the fixed molecular configuration are found to be p‐type semiconductors exhibiting excellent unipolar hole mobilities up to 0.22 cm² V^?1 s^?1, which is one order of magnitude higher than that of the parent IP‐O and is even comparable to that of QQT(CN)4‐based single‐crystal field‐effect transistors (FET). DTIPs exhibit better photovoltaic performance than their aromatic bithieno[3,4‐b]thiophene (BTT) counterparts with an optimal power‐conversion efficiency (PCE) of 4.07 %.     

Synthesis and Electrochemical Studies of Bingel–Hirsch Derivatives of M3N@Ih‐C80 (M=Sc,Lu)

Bingel–Hirsch derivatives of the trimetallic nitride template endohedral metallofullerenes (TNT‐EMFs) Sc₃N@I_h‐C₈₀ and Lu₃N@I_h‐C₈₀ were prepared by reacting these compounds with 2‐bromodiethyl malonate, 2‐bromo‐1,3‐dipyrrolidin‐1‐ylpropane‐1,3‐dionate bromide, and 9‐bromo fluorene. The mono‐adducts were isolated and their ¹H NMR spectra showed that the addition occurred with high regioselectivity at the [6,6] bonds of the I_h‐C₈₀ fullerene cage. Electrochemical analysis showed that the reductive electrochemistry behavior of these derivatives is irreversible at a scan rate of 100 mV s^?1, which is comparable to the behavior of the pristine fullerene species. The first reduction potential of each derivative is either cathodically or anodically shifted by a different value, depending on the attached addend. Bis‐adducts containing EtOOC‐C‐COOEt and HC‐COOEt addends were isolated by HPLC and in the case of Sc₃N@I_h‐C₈₀ the first reduction potential exhibits a larger shift towards negative potentials when compared to the mono‐adduct. This observation is important for designing acceptor materials for the construction of bulk heterojunction (BHJ) organic solar cells, since the polyfunctionalization not only increases the solubility of the fullerene species but also offers a promising approach for bringing the LUMO energy levels closer for the donor and the acceptor materials.     

Multielectron Redox Chemistry of a Neutral,NIR‐Active,Indigo‐Pillared ReI‐Based Triangular Metalloprism

Self‐assembled, hexarhenium(I), triangular metalloprism compound [{(CO)₃Re(μ‐ 2 )Re(CO)₃}₃(μ₃‐ 1 )₂] ( 3 ) featuring three bis‐chelating pillarlike indigo dianions (μ‐ 2 ), each of which connects two fac‐Re(CO)₃ cores, which are interconnected by a tritopic N donor, that is, a 2,4,6‐tris(4‐pyridyl)‐1,3,5‐triazine (μ₃‐ 1 , tPyTz) ligand, has been synthesized in high yield and characterized. Metalloprism 3 exhibits a strong absorption in the near‐infrared (NIR) region. The reversible, multielectron redox properties of the electrogenerated 3 ⁿ species, where n=3+, 0, 3?, 4?, 5?, 8?, in the visible and especially in the NIR region were investigated in THF solution by cyclic voltammetry (CV), chronocoulometry, EPR spectroscopy, and thin‐layer UV/Vis/NIR spectroelectrochemistry (SEC). Stepwise, site‐specific electrochemical reductions lead to the formation of a series of highly stable ion (radical) species in which electrons associated with μ‐ 2 or μ₃‐ 1 components of the molecule can be clearly distinguished. An EPR investigation revealed interaction of unpaired electrons with the metal nuclei (^185,187Re, I=5/2) in the reduced intermediates. The framework has C₂ symmetry, and accidental degeneracies suffice. Detailed theoretical calculations by structure‐based DFT confirm that the triply degenerate HOMO has ≥70 % indigo character with a sizable dπ‐Re character, while the LUMO is dominated by the triply degenerate indigo ligands, and the LUMO+1 by doubly degenerate tPyTz ligands. A comparison of 3 and previously reported 2,2′‐bis‐benzimidazolate‐ (BiBzlm) or alkoxy‐pillared Re^I metalloprisms indicates a very low switching potential with a potential window of less than 1 V and reversibly accessible optical properties with higher stability of the intermediates. The properties exhibited by 3 appear to be due to the slight tuning of the bridging ligand from N,N^? to N,O^?.     

SnS‐Quantum Dot Solar Cells Using Novel TiC Counter Electrode and Organic Redox Couples

Low‐cost quantum‐dot sensitized solar cells (QDSSCs) were fabricated by using the earth‐abundant element SnS quantum dot, novel TiC counter electrodes, and the organic disulfide/thiolate (T₂/T^?) redox couple, and reached an efficiency of 1.03 %. QDSSCs based on I^?/I₃^?, T₂/T^?, and S^2?/S_x^2? redox couples were assembled to study the role of the redox couples in the regeneration of sensitizers. Charge‐extraction results reveal the reasons for the difference in J_SC in three QDSSCs based on I^?/I₃^?, T₂/T^?, and S^2?/S_x^2? redox couples. The catalytic selectivity of TiC and Pt towards T₂/T^? and I^?/I₃^? redox couples was investigated using Tafel polarization and electrochemical impedance analysis. These results indicated that Pt and TiC show a similar catalytic selectivity for I^?/I₃^?. However, TiC possesses better catalytic activity for T₂/T^? than for I^?/I₃^?. These results indicate the great potential of transition metal carbide materials and organic redox couples used in QDSSCs.     

Bifunctional Ion‐Selective Electrode Based on C60‐Cryptand 22 for Silver and Iodine Ions

Fullerence C60‐cryptand 22 was prepared and successfully applied as the electric carrier in the PVC electrode membrane of a bifunctional ion‐selective electrode for cations, e.g., Ag⁺ ions as well as anions, e.g., I^? ions. The bifunctional ion‐selective electrode based on C60‐cryptand 22 can be applied as a Silver (Ag⁺) ion selective electrode with an internal electrode solution of 10^?3 M AgNO₃ in water (pH = 6.3), or as an Iodide (I^?) ion selective electrode with an acidic internal electrode solution of 10^?4 M KI_(aq) (pH = 2) in which the cryptand 22 is protonated, and the C60‐cryptand 22 is changed to C60‐Cryptand22–H⁺ and becomes an anionic electro‐carrier to absorb the I^? ion. The Ag⁺ ion selective electrode based on C60‐cryptand 22 gave a linear response with a near‐Nernstian slope (59.5 mV decade^?1) within the concentration range 10^?1‐10^?3 M Ag⁺_(aq). The Ag⁺ ion electrode exhibited comparatively good selectivity for silver ions, over other transition‐metal ions, alkali and alkaline earth metal ions. The Ag⁺ ion selective electrode with good stability and reproducibility was successfully used for the titration of Ag⁺_(aq) with Cl^? ions. The Iodide (I^?) Ion selective electrode based on protonated C60–cryptand22‐H⁺ also showed a linear response with a nearly Nernstian slope (58.5 mV decade^?1) within 10^?1 ‐ 10^?3 M I^? _(aq) and exhibited good selectivity for I^? ions and had small selectivity coefficients (10^?2–10^?3) for most of other anions, e.g., F^? , OH^?, CH₃COO^?, SO₄^2?, CO₃^2?, CrO₄^2?, Cr₂O₇^2? and PO₄^3? ions.     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Redox Sorption and Recovery of Silver Ions as Silver Nanocrystals on Poly(aniline‐co‐5‐sulfo‐2‐anisidine) Nanosorbents

Poly[aniline(AN)‐co‐5‐sulfo‐2‐anisidine(SA)] nanograins with rough and porous structure demonstrate ultrastrong adsorption and highly efficient recovery of silver ions. The effects of five key factors—AN/SA ratio, Ag^I concentration, sorption time, ultrasonic treatment, and coexisting ions—on Ag^I adsorbability were optimized, and AN/SA (50/50) copolymer nanograins were found to exhibit much stronger Ag^I adsorption than polyaniline and all other reported sorbents. The maximal Ag^I sorption capacity of up to 2034 mg g^?1 (18.86 mmol g^?1) is the highest thus far and also much higher than the maximal Hg‐ion sorption capacity (10.28 mmol g^?1). Especially at ≤2 mM Ag^I, the nanosorbents exhibit ≥99.98 % adsorptivity, and thus achieve almost complete Ag^I sorption. The sorption fits the Langmuir isotherm well and follows pseudo‐second‐order kinetics. Studies by IR, UV/Vis, X‐ray diffraction, polarizing microscopy, centrifugation, thermogravimetry, and conductivity techniques showed that Ag^I sorption occurs by a redox mechanism mainly involving reduction of Ag^I to separable silver nanocrystals, chelation between Ag^I and ? NH? /? N?/? NH₂/ ? SO₃H/? OCH₃, and ion exchange between Ag^I and H⁺ on ? SO₃^?H⁺. Competitive sorption of Ag^I with coexisting Hg, Pb, Cu, Fe, Al, K, and Na ions was systematically investigated. In particular, the copolymer nanoparticles bearing many functional groups on their rough and porous surface can be directly used to recover and separate precious silver nanocrystals from practical Ag^I wastewaters containing Fe, Al, K, and Na ions from Kodak Studio. The nanograins have great application potential in the noble metals industry, resource reuse, wastewater treatment, and functional hybrid nanocomposites.     

Halide‐Anion Binding by Singly and Doubly N‐Confused Porphyrins

The halide‐binding properties of N‐confused porphyrin (NCP, 1 ) and doubly N‐confused porphyrins (trans‐N₂CP ( 2 ), cis‐N₂CP ( 3 )) were examined in CH₂Cl₂. In the free‐base forms, cis‐N₂CP ( 3 ) showed the highest affinity to each anion (Cl^?, Br^?, I^?) with association constants K_a=7.8×10³, 1.9×10³, and 5.8×10² M ^?1, respectively. As metal complexes, on the other hand, trans‐N₂CP 2–Cu exhibited the highest affinity to Cl^?, Br^?, and I^? with K_a=9.0×10⁴, 2.7×10⁴, and 1.9×10³ M ^?1, respectively. The corresponding K_a values for cis‐N₂CP 3–Cu and NCP 1–Cu were about 1/10 and 1/2, respectively, of those of 2–Cu . With the help of density functional theory (DFT) calculations and complementary affinity measurements of a series of trisubstituted N‐confused porphyrins, the efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron‐deficient C₆F₅ groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability. The orientation and magnitude of the dipole moments in NCPs were suggested to be important factors in the differentiation of the affinity for anions.     

Face‐Capped M4L4 Tetrahedral Metal–Organic Cage: Iodine Capture and Release,Ion Exchange,and Electrical Conductivity

An M⁴L₄ type metal–organic cage (MOC‐19) has been synthesized from the one‐pot reaction of tri(pyridinylmethylene)phenylbenzeneamine (TPBA) with hydrated Zn(ClO₄)₂ under mild conditions and characterized by single‐crystal X‐Ray diffraction. Iodine capture studies show that the porous crystals of MOC‐19 exhibit a versatile behavior to accumulate iodine species not only in vapor (for I₂) but also in solution (for I₂ and I₃^?), and anion‐exchange experiments indicate the capacity to extract IO₃^? anions from aqueous solution. Enrichment of iodine species from KI/I₂ aqueous solution proceeds facilely, revealing a pseudo‐second‐order kinetics of I₃^? adsorption. Furthermore, the electrical conductivity of MOC‐19 single crystals could be significantly altered by I₂ inclusion.     

Synthesis,Structures, and Properties of Crystalline Salts with Radical Anions of Metal‐Containing and Metal‐Free Phthalocyanines

Radical anion salts of metal‐containing and metal‐free phthalocyanines [MPc(3?)]^.?, where M=Cu^II, Ni^II, H₂, Sn^II, Pb^II, Ti^IVO, and V^IVO ( 1 – 10 ) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C?N_imine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1 – 10 show new bands at 833–1041 nm in the NIR range, whereas the Q‐ and Soret bands are blue‐shifted by 0.13–0.25 eV (38‐92 nm) and 0.04–0.07 eV (4–13 nm), respectively. Radical anions with Ni^II, Sn^II, Pb^II, and Ti^IVO have S=1/2 spin state, whereas [Cu^IIPc(3?)]^.? and [V^IVOPc(3?)]^.? containing paramagnetic Cu^II and V^IVO have two S=1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal‐free phthalocyanine radical anions [H₂Pc(3?)]^.? (linewidth of 0.08–0.24 mT), broad EPR signals are manifested (linewidth of 2–70 mT) with g‐factors and linewidths that are strongly temperature‐dependent. Salt 11 containing the [Na^IPc(2?)]^? anions as well as previously studied [Fe^IPc(2?)]^? and [Co^IPc(2?)]^? anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3?)]^.? in 1 – 10 .     

Naphthodithiophene‐Diketopyrrolopyrrole‐Based donor–Acceptor alternating π‐Conjugated polymers for Organic thin‐Film transistors

Novel naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) and diketopyrrolopyrrole (DPP)‐containing donor‐acceptor conjugated polymers (PNDTDPPs) with different branched side chains were synthesized via Pd(0)‐catalyzed Stille coupling reaction. Octyldodecyl (OD) and dodecylhexadecyl (DH) groups were tethered to the DPP units as the side chains. The soluble fraction of PNDTDPP‐OD polymer in chloroform has much lower molecular weight than that of PNDTDPP‐DH polymer. PNDTDPP‐DH polymer bearing relatively longer DH side chains exhibited much better charge‐transport behavior than PNDTDPP‐OD polymer with shorter OD side chains. The thermally annealed PNDTDPP‐DH polymer thin films exhibited an outstanding charge carrier mobility of ～1.32 cm² V^?1 s^?1 (I_on/I_off ～ 10⁸) measured under ambient conditions, which is almost six times higher than that of thermally annealed PNDTDPP‐OD polymer thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5280–5290     

Phenacyl–Thiophene and Quinone Semiconductors Designed for Solution Processability and Air‐Stability in High Mobility n‐Channel Field‐Effect Transistors

Electron‐transporting organic semiconductors (n‐channel) for field‐effect transistors (FETs) that are processable in common organic solvents or exhibit air‐stable operation are rare. This investigation addresses both these challenges through rational molecular design and computational predictions of n‐channel FET air‐stability. A series of seven phenacyl–thiophene‐based materials are reported incorporating systematic variations in molecular structure and reduction potential. These compounds are as follows: 5,5′′′‐bis(perfluorophenylcarbonyl)‐2,2′:5′,‐ 2′′:5′′,2′′′‐quaterthiophene ( 1 ), 5,5′′′‐bis(phenacyl)‐2,2′:5′,2′′: 5′′,2′′′‐quaterthiophene ( 2 ), poly[5,5′′′‐(perfluorophenac‐2‐yl)‐4′,4′′‐dioctyl‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene) ( 3 ), 5,5′′′‐bis(perfluorophenacyl)‐4,4′′′‐dioctyl‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene ( 4 ), 2,7‐bis((5‐perfluorophenacyl)thiophen‐2‐yl)‐9,10‐phenanthrenequinone ( 5 ), 2,7‐bis[(5‐phenacyl)thiophen‐2‐yl]‐9,10‐phenanthrenequinone ( 6 ), and 2,7‐bis(thiophen‐2‐yl)‐9,10‐phenanthrenequinone, ( 7 ). Optical and electrochemical data reveal that phenacyl functionalization significantly depresses the LUMO energies, and introduction of the quinone fragment results in even greater LUMO stabilization. FET measurements reveal that the films of materials 1 , 3 , 5 , and 6 exhibit n‐channel activity. Notably, oligomer 1 exhibits one of the highest μ_e (up to ≈0.3 cm² V^?1 s^?1) values reported to date for a solution‐cast organic semiconductor; one of the first n‐channel polymers, 3 , exhibits μ_e≈10^?6 cm² V^?1 s^?1 in spin‐cast films (μ_e=0.02 cm² V^?1 s^?1 for drop‐cast 1 : 3 blend films); and rare air‐stable n‐channel material 5 exhibits n‐channel FET operation with μ_e=0.015 cm² V^?1 s^?1, while maintaining a large I_on:off=10⁶ for a period greater than one year in air. The crystal structures of 1 and 2 reveal close herringbone interplanar π‐stacking distances (3.50 and 3.43 Å, respectively), whereas the structure of the model quinone compound, 7 , exhibits 3.48 Å cofacial π‐stacking in a slipped, donor‐acceptor motif.     

Redox‐Switchable Ring‐Closing Metathesis: Catalyst Design,Synthesis, and Study

High yielding syntheses of 1‐(ferrocenylmethyl)‐3‐mesitylimidazolium iodide ( 1 ) and 1‐(ferrocenylmethyl)‐3‐mesitylimidazol‐2‐ylidene ( 2 ) were developed. Complexation of 2 to [{Ir(cod)Cl}₂] (cod=cis,cis‐1,5‐cyclooctadiene) or [Ru(PCy₃)Cl₂(?CH‐o‐O‐iPrC₆H₄)] (Cy=cyclohexyl) afforded 3 ([Ir( 2 )(cod)Cl]) and 5 ([Ru( 2 )Cl₂(?CH‐o‐O‐iPrC₆H₄)]), respectively. Complex 4 ([Ir( 2 )(CO)₂Cl]) was obtained by bubbling carbon monoxide through a solution of 3 in CH₂Cl₂. Spectroelectrochemical IR analysis of 4 revealed that the oxidation of the ferrocene moiety in 2 significantly reduced the electron‐donating ability of the N‐heterocyclic carbene ligand (ΔTEP=9 cm^?1; TEP=Tolman electronic parameter). The oxidation of 5 with [Fe(η⁵‐C₅H₄COMe)Cp][BF₄] as well as the subsequent reduction of the corresponding product [ 5 ][BF₄] with decamethylferrocene (Fc*) each proceeded in greater than 95 % yield. Mössbauer, UV/Vis and EPR spectroscopy analysis confirmed that [ 5 ][BF₄] contained a ferrocenium species, indicating that the iron center was selectively oxidized over the ruthenium center. Complexes 5 and [ 5 ][BF₄] were found to catalyze the ring‐closing metathesis (RCM) of diethyl diallylmalonate with observed pseudo‐first‐order rate constants (k_obs) of 3.1×10^?4 and 1.2×10^?5 s^?1, respectively. By adding suitable oxidants or reductants over the course of a RCM reaction, complex 5 was switched between different states of catalytic activity. A second‐generation N‐heterocyclic carbene that featured a 1′,2′,3′,4′,5′‐ pentamethylferrocenyl moiety ( 10 ) was also prepared and metal complexes containing this ligand were found to undergo iron‐centered oxidations at lower potentials than analogous complexes supported by 2 (0.30–0.36 V vs. 0.56–0.62 V, respectively). Redox switching experiments using [Ru( 10 )Cl₂(?CH‐o‐O‐iPrC₆H₄)] revealed that greater than 94 % of the initial catalytic activity was restored after an oxidation–reduction cycle.     

Synthesis,properties, and field effect transistor characteristics of new thiophene‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline‐thiophene‐based conjugated polymers

Four new conjugated copolymers based on the moiety of bis(4‐hexylthiophen‐2‐yl)‐6,7‐diheptyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline (BTHTQ) were synthesized and characterized, including poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) (PBTHTQ), poly‐(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo‐[3,4‐g]quinoxaline‐alt‐2,5‐thiophene) (PTTHTQ), poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl) [1,2,5]‐thiadiazolo‐[3,4‐g]quinoxaline‐alt‐9,9‐dioctyl‐2,7‐fluore‐ne) (PFBTHTQ), and poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline‐alt‐1,4‐bis(decyloxy)phenylene) (PPBTHTQ). The λ_max of PBTHTQ, PTTHTQ, PFBTHTQ, and PPBTHTP thin films was shown at 780, 876, 734, and 710 nm, respectively, with the corresponding optical band gaps (E) of 1.31, 1.05, 1.40, and 1.43 eV. The relatively small band gaps of the synthesized polymers suggested the significance of intramolecular charge transfer between the donor and TQ moiety. The estimated hole mobilities of PBTHTQ, PTTHTQ, and PFBTHTQ‐based field effect transistor devices using CHCl₃ solvent were 8.5 × 10^?5, 8.5 × 10^?4, and 2.8 × 10^?5 cm² V^?1 s^?1, respectively, but significantly enhanced to 1.6 × 10^?4, 3.8 × 10^?3, and 1.5 × 10^?4 cm² V^?1 s^?1 using high boiling point solvent of chlorobenzene (CB). The higher hole mobility of PTTHTQ than the other two copolymers was attributed from its smaller band gap or ordered morphology [wormlike (chloroform) or needle‐like (CB)]. The characteristics of small band gap and high mobility suggest the potential applications of the BTHTQ‐based conjugated copolymers in electronic and optoelectronic devices. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6305–6316, 2008     

Synthesis and characterization of fused‐thiophene containing naphthalene diimide n‐type copolymers for organic thin film transistor and all‐polymer solar cell applications

Naphthalene diimide copolymers are attractive n‐type materials due to their high electron affinities, high electron mobilities, and exceptional stability. Herein, we report a series of NDI‐fused‐thiophene based copolymers with each copolymer differing in the number of fused thiophenes in the donor monomer. Increasing the number of fused‐thiophene moieties within an NDI‐copolymer backbone is shown to not only enable tuning of the electronic structure but also improve charge mobilities within the active layer of organic field‐effect transistors. Electron mobilities and on/off ratios as high as 0.012 cm² V^?1 s^‐1 and I_on/I_off > 10⁵ were measured from n‐channel thin‐film transistors fabricated using NDI‐xfTh copolymers. Bulk heterojunction solar cell devices were also fabricated from the NDI‐xfTh copolymer series in blends with poly(3‐hexylthiophene) (P3HT) with PNDI‐4fTh ‐ based devices yielding the largest J_sc (0.57 mA cm^?2) and fill factor (55%) in addition to the highest measured PCE for this series (0.13%). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4061–4069     

Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]^? ( 1 ^?; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ^? acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄^?, ClO₄^?, ReO₄^?). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au? S and Au? P bonds, which is essential for metallaring expansion and contraction.     

A Highly Active N‐Heterocyclic Carbene Manganese(I) Complex for Selective Electrocatalytic CO2 Reduction to CO

We report here the first purely organometallic fac‐[Mn^I(CO)₃(bis‐^MeNHC)Br] complex with unprecedented activity for the selective electrocatalytic reduction of CO₂ to CO, exceeding 100 turnovers with excellent faradaic yields (η_CO≈95 %) in anhydrous CH₃CN. Under the same conditions, a maximum turnover frequency (TOF_max) of 2100 s^?1 was measured by cyclic voltammetry, which clearly exceeds the values reported for other manganese‐based catalysts. Moreover, the addition of water leads to the highest TOF_max value (ca. 320 000 s^?1) ever reported for a manganese‐based catalyst. A Mn^I tetracarbonyl intermediate was detected under catalytic conditions for the first time.