Tetrathiafulvalene Units Research Articles

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Binucleating Jäger-type {(N2O2)2}4- ligands: magnetic and electronic interactions of Fe(II), Ni(II) and Cu(II) across an in-plane TTF-bridge.

The simultaneous presence of different electrophores provides an interesting playground for responsive materials. Herein, we present the incorporation of a twice-reversibly oxidizable tetrathiafulvalene (TTF) unit into a binucleating ligand, bridging two metal centers in a fully conjugated plane. A two-step synthesis scheme gave the D2h symmetric Schiff base-like ligand H4L in moderate yields from which the corresponding copper(II) [Cu2L], nickel(II) [Ni2L], [Ni2L(py)4] and iron(II) complexes [Fe2L(py)4], [Fe2L(dmap)4] and [Fe2L(bpee)2]·1 Tol could be obtained. Characterization was performed through 1H-NMR, IR, UV-vis and 57Fe-Mössbauer spectroscopy, SQUID magnetometry and cyclic voltammetry, supported by density functional theory (DFT) calculations. Single crystal X-ray analysis of [Ni2L(py)4] revealed six-coordinate paramagnetic centers, whereas [Ni2L] underwent gradual coordination induced spin state switching (CISSS) in solution. The magnetic independence of both metal centers is echoed by close-to-ideal Curie-plots of the [Cu2L] system and the gradual spin crossover of all iron(II) compounds. By contrast, cyclic voltammetry measurements in solution indicated oxidation-dependent TTF-metal interactions, as well as metal-metal interactions. The reversible TTF-borne events in H4L and [Ni2L] are overlaid with metal-borne events in the case of [Fe2L(py)4], as is corroborated by an analysis of the frontier orbital landscapes and through diagnostic spectral features upon chemical oxidation.

Mechanistic studies of isomeric [2]rotaxanes consisting of two different tetrathiafulvalene units reveal that the movement of cyclobis(paraquat-p-phenylene) can be controlled.

Controlling the movement in artificial molecular machines is a key challenge that needs to be solved before their full potential can be harnessed. In this study, two isomeric tri-stable [2]rotaxanes 1·4PF6 and 2·4PF6 incorporating both a tetrathiafulvalene (TTF) and a monopyrrolotetrathiafulvalene (MPTTF) unit in the dumbbell component have been synthesised to measure the energy barriers when the tetracationic cyclobis(paraquat-p-phenylene) (CBPQT4+) ring moves across either a TTF2+ or an MPTTF2+ dication. By strategically exchanging one of the thiomethyl barriers on either the TTF unit or the MPTTF unit with the bulkier thioethyl group, the movement of the CBPQT4+ ring in 14+ and 24+ can be controlled to take place in only one direction upon tetra-oxidation. Cyclic voltammetry and 1H NMR spectroscopy were used to investigate the switching mechanism and it was found that upon tetra-oxidation of 14+ and 24+, the CBPQT4+ ring moves first to a position where it is located between the TTF2+ and MPTTF2+ dications producing high-energy co-conformations which slowly interconvert into thermodynamically more stable co-conformations. The kinetics of the movement occurring in the tetra-oxidised [2]rotaxanes 18+ and 28+ were studied at different temperatures allowing the free energy of the transition state, when CBPQT4+ moves across TTF2+ (21.5 kcal mol-1) and MPTTF2+ (20.3 kcal mol-1) at 298 K, to be determined. These results demonstrate for the first time that the combination of a TTF and an MPTTF unit can be used to induce directional movement of the CBPQT4+ ring in molecular machines with a 90% efficiency.

Progressive framework designing and photocurrent responsive tuning based on tetra(4-pyridyl)-tetrathiafulvalene ligand

Although metal−organic frameworks (MOFs) based on redox-active tetrathiafulvalene (TTF) unit show good photocurrent performance, related reports about systematically elucidating the relationship between framework and photocurrent propriety are still scarce. Herein, three topologically and dimensionally tunable MOFs based on the redox active tetra(4-pyridyl)-tetrathiafulvalene (TTF(py)4), terephthalic acid (TPA), 4,4′-biphenyldicarboxylic acid (BDA) and 4,4′-oxybisbenzoic acid (OBA) ligand, namely as [Cd(TTF(py)4)2(TPA)2]n (1), [Zn(TTF(py)4)2(BDA)2]n (2) and {[Zn(TTF(py)4)2(OBA)2] H2O}n (3), were prepared via utilizing solvothermal method. Single crystal diffraction analysis showed that the structural adjustment of auxiliary ligands can realize the supramolecular networks with different dimensions well. The rod-shaped auxiliary ligands can endow MOFs (complex 1 and 2) with better three-dimensional (3D) extension skeleton. As a comparison, the fold-like auxiliary ligand (OBA) enabled complex 3 to extend along the two-dimensional (2D) backbone. In addition, all complexes exhibit redox activity and photocurrent responsive properties. Interestingly, complex 3 linking by fold-like auxiliary ligand shows nearly 10 times higher photocurrent intensity than traditional TTF unit. This work sheds some light on the construction of complexes with high photocurrent response properties through rational tuning of MOFs dimensions.

Stabilizing Indigo Z‐Isomer through Intramolecular Associations of Redox‐Active Appendages

AbstractPhotoswitchable small molecules, such as N,N’‐disubstituted indigos, have received great interest within fields such as pharmacology, energy storage, and functional materials, as they represent key building blocks for reversible and non‐invasive control of chemical processes. However, to ensure applicability of photochromic systems it is of paramount importance to manipulate the photostationary state. In this work, we achieved this by tethering two redox‐active indenofluorene‐extended tetrathiafulvalene units to an N,N’‐disubstituted indigo photoswitch. Upon two‐electron oxidation, we observe significantly enhanced stability of the Z‐isomer, compared to the neutral compound, illustrated by a substantial increase in the half‐life from 0.48 seconds to 22 hours. This remarkable stabilization is ascribed to formation of strong, intramolecular π‐dimers between the oxidized subunits.

π-Conjugated Molecules Containing Tetrathiafulvalene and Benzo[b]phosphole Oxide: Synthesis, Structure, and Electrochemical and Optical Properties

Three new π-conjugated molecules containing a tetrathiafulvalene (TTF) unit and a benzo[b]phosphole oxide unit were successfully synthesized. X-ray structural analysis revealed that the benzo[b]phosphole oxide unit exhibits high planarity, whereas the TTF unit adopts a bending structure. Electrochemical analysis by cyclic voltammetry revealed two pairs of redox waves derived from the TTF site. The absorption bands were almost identical to those of the TTF and benzo[b]phosphole oxide moieties, although their fluorescence was significantly quenched by intramolecular electron transfer.

Theoretical prediction on photoelectric and supramolecular properties of benzoquinone-tetrathiafulvalene macrocyclic molecules.

Benzoquinone has the ability to serve as an electron acceptor, and tetrathiafulvalene has the ability to serve as an electron donor. Based on the facts above, this work creatively cycles the benzoquinone unit and the tetrathiafulvalene unit alternately into macrocyclic molecules, the cyclopolymers of benzoquinone-tetrafluorene (C[n]QTTF, n = 3~6). To explore their structure and properties, the M06-2X functional of density functional theory (DFT) with 6-311g(d) basis set was used to optimize the ground-state structures of C[n]QTTF. Based on the stable configurations of the ground states, the electronic structure property is analyzed systematically. The results show that these macrocyclic molecules have excellent electron transport capability and electrochemical activity. Then, the electron absorption spectra of each system are carried out by using time-dependent density functional theory (TD-DFT) at the M062X/6-311+G(d) level. It turns out that their maximum absorption wavelengths are all in the visible range. Further calculation suggests that C[n]QTTF can also be characterized with one-dimensional self-assembly, double-walled assembly, and the host-guest inclusion performance, based on which it gains a variety of supramolecular structures. In summary, the benzoquinone-tetrafluorofurene macrocyclic molecules predicted by DFT calculations may be of assistance to the potential applications in organic electronics and supramolecular chemistry.

Synthesis and properties of supramolecular gels based on tetrathiafulvalene and cyanobiphenyl units

ABSTRACT For the development of self-assembly donor-σ-acceptor (D-σ-A) molecules, a series of D-σ-A low-molecular mass organogelators, consisting of tetrathiafulvalene (D) and cyanobiphenyl (A) connected by a thioalkanoyloxy spacer of varying lengths modified with hydrophobic chains incorporating amide groups on the side, was designed and readily synthesized. Their gelation properties were studied. The results showed that the gelation capability of these compounds was highly dependent on the alkyl chain length in the spacer group and the TTF and cyanobiphenyl units. Derivative 1a with short alkyl chain (n = 4) efficiently gelated in some aromatic solvents, forming opaque organogels. These gelators reacted with F4TCNQ to form stable charge-transfer complex gels in ethanol. Clear evidence of self-assembled micro/nanoflower, fibrous, or tubular morphologies in gelation state was obtained by scanning electron microscopy. It was found that the molecules adopted lamellar and rectangular columnar molecular packing models in the gel phase by X-ray diffraction. The native gels underwent a reversible gel-sol phase transition upon exposure to external stimuli. The gel-sol transition of the organogel was stimulated by the addition of fluoride anions. Interestingly, all gels showed an irreversible gel-sol transition triggered by TFA and TEA. The formation of flower-like morphologies of TTF-based derivatives in the gel state was observed.

Twisted chromophore assist to tetrathiafulvalene-spiropyran hybrid driving four-state molecular switch

A series of novel molecular hybrids, in which tetrathiafulvalene (TTF) unit and spiropyran (SP) core are covalently linked to various typical π-conjugated bridges, has been designed based on auxiliary donors and acceptors model and twisted intramolecular charge transfer (TICT) strategy. And the second-order nonlinear optical (NLO) responses of these molecular hybrids have been investigated by using density functional theory (DFT) calculations. The results show that grafting of the TTF unit and SP core to the twisted chromophore (TC) can effectively enhances second-order NLO responses. The promoting effect of enhancing NLO response can be attributed to a strongly favorable charge transfer in TTF-TC-SP hybrid. More importantly, we have found that this TTF-TC-SP hybrid with donor-π-conjugated bridge-acceptor structure can efficiently switch the first hyperpolarizability across four states via redox and photochemical stimuli. Meanwhile, time-dependent (TD) DFT calculations were carried out to probe the origin of the second-order NLO response of TTF-TC-SP molecular hybrid. All these findings provide a clear and well understanding of the relationship between the tunable first hyperpolarizability and electronic structure. We hope these findings would be very useful to guide the search for potential polymorphic molecular switch.

Iron(II) Spin Crossover Complexes Based on a Redox Active Equatorial Schiff-Base-Like Ligand.

In this work, two iron(II) coordination compounds with a N2O2 coordinating Schiff base-like ligand bearing a redox active tetrathiafulvalene (TTF) unit and pyridine or trans-1,2-bis(4-pyridylethylene) as an axial ligand are synthesized. Crystals suitable for single X-ray structure analysis were obtained for the new ligand. The complexes were characterized by magnetic susceptibility measurements, T-dependent UV-vis spectroscopy, and cyclic voltammetry. Both complexes display spin transition behavior below room temperature with T1/2 values of 146 and 156 K. The mononuclear iron(II) complex [FeTTFL(py)2] is relatively stable up to 400 K compared to similar complexes, showing no loss of axial ligands upon heating. Temperature dependent Mössbauer spectroscopy was conducted for the coordination polymer {[FeTTFL(bpee)]}n to get more information regarding the origin of the stepwise spin crossover (SCO) behavior observed in the magnetic measurements. The change of the spin state is accompanied by a change of the optical properties, which can be monitored by VT-UV-vis spectroscopy for the mononuclear complex and has been analyzed in theoretical studies. The redox behavior of the iron(II) complexes reveals three reversible redox steps which are located at the iron center and at the TTF unit of the ligand. Oxidation of the TTF unit induces characteristic changes in the UV-vis spectrum that can be followed by spectroelectrochemical UV-vis spectroscopy. Addressing the potential of the iron-centered redox process results in similar changes in the UV-vis spectrum, which indicates an electronic coupling of the redox active unit with the metal center under certain circumstances.

Electrochemical Switching of a Fluorescent Molecular Rotor Embedded within a Bistable Rotaxane.

We report how the nanoconfined environment, introduced by the mechanical bonds within an electrochemically switchable bistable [2]rotaxane, controls the rotation of a fluorescent molecular rotor, namely, an 8-phenyl-substituted boron dipyrromethene (BODIPY). The electrochemical switching of the bistable [2]rotaxane induces changes in the ground-state coconformation and in the corresponding excited-state properties of the BODIPY rotor. In the starting redox state, when no external potential is applied, the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles the tetrathiafulvalene (TTF) unit on the dumbbell component, leaving the BODIPY rotor unhindered and exhibiting low fluorescence. Upon oxidation of the TTF unit to a TTF2+ dication, the CBPQT4+ ring is forced toward the molecular rotor, leading to an increased energy barrier for the excited state to rotate the rotor into the state with a high nonradiative rate constant, resulting in an overall 3.4-fold fluorescence enhancement. On the other hand, when the solvent polarity is high enough to stabilize the excited charge-transfer state between the BODIPY rotor and the CBPQT4+ ring, movement of the ring toward the BODIPY rotor produces an unexpectedly strong fluorescence signal decrease as the result of photoinduced electron transfer from the BODIPY rotor to the CBPQT4+ ring. The nanoconfinement effect introduced by mechanical bonding can effectively lead to modulation of the physicochemical properties as observed in this bistable [2]rotaxane. On account of the straightforward synthetic strategy and the facile modulation of switchable electrochromic behavior, our approach could pave the way for the development of new stimuli-responsive materials based on mechanically interlocked molecules for future electro-optical applications, such as sensors, molecular memories, and molecular logic gates.

Redox-Driven Folding, Unfolding, and Refolding of Bis(tetrathiafulvalene) Molecular Switch.

We report redox-driven folding, unfolding, and refolding motions of a synthetic molecular system, in which two tetrathiafulvalene (TTF) units are tethered onto a conformationally rigid yet torsionally flexible π-conjugated backbone. Upon one-electron oxidation, this molecular switch undergoes swiveling motions from a fully relaxed and freely rotating Z-shaped conformation to a compact folded conformation stabilizing π-stacked radical species. Subsequent one-electron oxidation produces dicationic intermediates, which either engage in intimate π-π interactions or transition to an open structure. Further oxidation, however, brings the molecule back to the initial conformation to minimize the repulsion between doubly-charged TTF units. Intriguingly, the reaction coordinates of this redox-driven structural change have strong dependence on the environment, such as the solvent (THF vs CH2Cl2) and supporting electrolyte (PF6- vs B(C6F5)4-). With a proper design, factors that are typically considered as "secondary effects" could dictate the solution dynamics and reaction pathways of structural folding and unfolding, all driven by controlled delivery of electrons.

Diverse π-π stacking motifs modulate electrical conductivity in tetrathiafulvalene-based metal-organic frameworks.

We report three electrically conductive metal-organic frameworks (MOFs) based on a tetrathiafulvalene linker and La3+. Depending on the solvent ratios and temperatures used in their solvothermal synthesis, these MOFs crystallize with different topologies containing distinct π-π stacking sequences of the ligand. Notably, their transport properties correlate rationally with the stacking motifs: longer S···S contact distances between adjacent ligands coincide with lower electrical conductivities and higher activation energies. Diffuse reflectance spectroscopic measurements reveal ligand-based intervalence charge transfer bands in each phase, implicating charge delocalization among mixed-valent tetrathiafulvalene units as the dominant mode of transport. Overall, these frameworks demonstrate how tuning the intermolecular interactions in MOFs serves as a route towards controlling their physical properties.

Modification of Side Chains of Conjugated Molecules and Polymers for Charge Mobility Enhancement and Sensing Functionality.

Organic semiconductors have received increasing attentions in recent years because of their promising applications in various optoelectronic devices. The key performance metric for organic semiconductors is charge carrier mobility, which is governed by the electronic structures of conjugated backbones and intermolecular/interchain π-π interactions and packing in both microscopic and macroscopic levels. For this reason, more efforts have been paid to the design and synthesis of conjugated frameworks for organic semiconductors with high charge mobilities. However, recent studies manifest that appropriate modifications of side chains that are linked to conjugated frameworks can improve the intermolecular/interchain packing order and boost charge mobilities. In this Account, we discuss our research results in context of modification of side chains in organic semiconductors for charge mobility enhancement. These include the following: (i) The lengths of alkyl chains in sulfur-rich thiepin-fused heteroacences can dramatically influence the intermolecular arrangements and orbital overlaps, ushering in different hole mobilities. Inversely, the lamellar stacking modes of alkyl chains in naphthalene diimide (NDI) derivatives with tetrathiafulvalene (TTF) units are affected by the structures of conjugated cores. (ii) The steric hindrances owing to the bulky branching chains can be weakened by partial replacement of the branching alkyl chains with linear ones for diketopyrrolopyrrole (DPP)-based D (donor)-A (acceptor) conjugated polymers. Such modification of side chains makes the polymer backbones more planar and thus interchain packing order and charge mobilities are improved. The incorporation of hydrophilic tri(ethylene glycol) (TEG) chains into the polymers also leads to improved interchain packing order. In particular, the polymer in which TEG side chains are distributed uniformly exhibits relatively high charge mobility without thermal annealing. (iii) The incorporation of urea groups in the side chains induces the polymer chains to pack more orderly and form large domains because of the additional H-bonding among urea groups. Accordingly, thin film mobilities of the conjugated D-A polymers with side chains entailing urea groups are largely boosted in comparison with those of polymers of the same backbones with either branching alkyl chains or branching/linear alkyl chains. (iv) The torsions of branching alkyl chains in conjugated D-A polymers can be inhibited to some extent upon incorporation of tiny amount of NMe4I in the thin film. As a result, the polymer thin films with NMe4I exhibit improved crystallinity, and charge mobilities can be boosted by more than 20 times. (v) Side chains with functional groups in the conjugated polymers can endow the thin film field-effect transistors (FETs) with sensing functionality. FETs with the conjugated polymer with -COOH groups in the side chains show sensitive, selective, and fast responses toward ammonia and amines, while FETs with the ultrathin films of the polymer containing tetra(ethylene glycol) (TEEG) in the side chains can sense alcohol vapors (in particular ethanol vapor) sensitively and selectively with fast response.

Synthesis and characterization of a doubly spin-labelled electrochemically driven molecular shuttle

The EPR properties of novel nitroxide-spin-labelled rotaxanes containing a tetrathiafulvalene (TTF) unit and a cyclobis(paraquat-p-phenylene) ring are described.

A Class of Electron-Transporting Vinylogous Tetrathiafulvalenes Constructed by the Dimerization of Core-Expanded Naphthalenediimides.

The combination of the (1,3-dithiol-2-ylidene)malononitrile (DTYM) and/or (1,3-dithiol-2-ylidene)acetonitrile (DTYA) moieties with naphthalenediimide (NDI) core affords two singly linked NDI-based dimers, (DTYM-NDI-DTYA)2 (D1) and (NDI-DTYA)2 (D2), which both contain a dicyano-substituted vinylogous tetrathiafulvalene (TTF) unit. The synthesis, thermal/optical/electrochemical properties of D1 and D2, and their primary applications in n-channel organic thin film transistors are studied. The results demonstrate that these NDI-fused vinylogous TTFs are excellent electron acceptors, and their further applications are promising.

Impact of mechanical bonding on the redox-switching of tetrathiafulvalene in crown ether-ammonium [2]rotaxanes.

Switchable crown ether-ammonium [2]rotaxanes with a redox-active tetrathiafulvalene (TTF) unit implemented in their wheels were synthesised and fully characterised. Reversible operation in two modes is possible, in which the [2]rotaxane's axle is either charged or neutral. Cyclic voltammetry experiments reveal the effects of mechanical bonding on the electrochemical properties of TTF and show the [2]rotaxanes to perform a distinct function in both modes. In the charged mode, redox-switching is dominated by strong electrostatic repulsion in the [2]rotaxane which subsequently leads to a macrocycle translation along the axle. In the non-charged mode, a selective energetic stabilisation of TTF radical cations is observed, which can be attributed to an interplay of weak electrostatic interactions between wheel and axle.

Multilevel Investigation of Charge Transport in Conjugated Polymers.

Conjugated polymers have attracted the world's attentions since their discovery due to their great promise for optoelectronic devices. However, the fundamental understanding of charge transport in conjugated polymers remains far from clear. The origin of this challenge is the natural disorder of polymers with complex molecular structures in the solid state. Moreover, an effective way to examine the intrinsic properties of conjugated polymers is absent. Optoelectronic devices are always based on spin-coated films. In films, polymers tend to form highly disordered structures at nanometer to micrometer length scales due to the high degree of conformational freedom of macromolecular chains and the irregular interchain entanglement, thus typically resulting in much lower charge transport properties than their intrinsic performance. Furthermore, a subtle change of processing conditions may dramatically affect the film formation-inducing large variations in the morphology, crystallinity, microstructure, molecular packing, and alignment, and finally varying the effective charge transport significantly and leading to great inconsistency over an order of magnitude even for devices based on the same polymer semiconductor. Meanwhile, the charge transport mechanism in conjugated polymers is still unclear and its investigation is challenging based on such complex microstructures of polymers in films. Therefore, how to objectively evaluate the charge transport and probe the charge transport mechanism of conjugated polymers has confronted the world for decades. In this Account, we present our recent progress on multilevel charge transport in conjugated polymers, from disordered films, uniaxially aligned thin films, and single crystalline micro- or nanowires to molecular scale, where a derivative of poly(para-phenylene ethynylene) with thioacetyl end groups (TA-PPE) is selected as the candidate for investigation, which could also be extended to other conjugated polymer systems. Our systematic investigations demonstrated that 3-4 orders higher charge transport properties could be achieved with the improvement of polymer chain order and confirmed efficient charge transport along the conjugated polymer backbones. Moreover, with downscaling to molecular scale, many novel phenomena were observed such as the largely quantized electronic structure for an 18 nm-long TA-PPE and the modulation of the redox center of tetrathiafulvalene (TTF) units on tunneling charge transport, which opens the door for conjugated polymers used in nanometer quantum devices. We hope the understanding of charge transport in PPE and its related conjugated polymer at multilevel scale in this Account will provide a new method to sketch the charge transport properties of conjugated polymers, and new insights into the combination of more conjugated polymer materials in the multilevel optoelectronic and other related functional devices, which will offer great promise for the next generation of electronic devices.

Bezoquinone Dimer Fused By the Tetrathiafulvalene Unit As an Orgunic Positive Electlode Material for Rechargeable Batteries

Recently, the development of a high performance rechargeable battery system without using any minor metal-based materials, especially in the positive-electrode is desired due to the increasing concern about the limited resources. One of the candidate categories is a series of redox active organic materials that contain no scarce metal resources. Organic materials are flexible and light-weight, and have a high degree of freedom in molecular design. Due to these unique characteristics, several types of organic compounds have already been proposed so far as positive electrode active materials. Among some categories, 1,4-benzoquinone (BQ) derivatives are reported to exhibit high capacities [1] since these derivative undergo a two-electron transfer type redox reaction per skeleton. However, their discharge potentials are usually lower than those of the inorganic competitors. This is related to the redox mechanism of the BQs, in which the electron accepter type carbonyl group receives an electron and a lithium cation during the discharge process. On the other hand, electron donor type tetrathiafulvalene (TTF) analogues, which release electrons and receive anions during the charge process, are known to exhibit a relatively high discharge potential [2], although their discharge capacities are not high enough. To satisfy the both high capacity and high discharge potential, we have focused on a fused structure (1) in which two BQ skeletons are crosslinked by one TTF unit. A high capacity of 441 mAh/g is expected for this compound, 1. In this paper, we synthesized 1 to evaluate its battery performance. The synthetic route for 1 is described in Fig. 1a. First, 4 was prepared in 32% yield by the P(OEt)3-mediated cross coupling of 2 [3] with 1.5 equiv. mol. of 3 [4] (lit. 45%, in the case of homo-coupling of 3 [3]. Then, 1 was prepared by a literature procedure [3] in 53% yield. An IEC R2032 coin-type cell composed of a positive electrode of 1 and a lithium metal sheet as a negative electrode was prepared to examine the battery performance. The positive electrode was prepared by mixing the powder of 1 with acetylene black as the conductive additive, and poly(tetrafluoroethylene) as the binder in the weight ratio of 1: 8: 1. The initial five cycles of charge-discharge curves of the prepared cell is shown in Fig. 1b. The observed initial discharge capacity of 259 mAh/g corresponds to 88% of the theoretical value of 294 mAh/g under the assumption of only the redox of the BQ moieties. The discharge capacities of second cycle was increased to 310 mAh/g. This capacity is 70% of the theoretical capacity in which six-electron transfer reaction per molecule is considered. This result undoubtedly indicates that both BQ and TTF moieties in the skeleton of 1 participate in the discharge process. The average potential of 2.84 V vs. Li/Li+ is higher than those of reported normal quinone derivatives [5] and the energy density was calculated to be 880 mWh/g. As shown in Fig. 1c, the electrode of 1 had a relatively good cycle stability: it maintained 206 mAh/g after 25 cycles. The results obtained in this paper suggests that fusing a donor and acceptor type redox units can be an effective strategy for designing a high energy density positive electrode material.

New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties.

A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3π-π*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry.