Optoelectronic conversion and polarization hysteresis in organic MISM and MISIM devices with DA-type single-component molecules.

Organic electronic devices offer various advantages, such as low cost and tunability. However, the organic semiconductors used in these devices have significant drawbacks, including instability in air and low carrier mobility. To address these challenges, we recently introduced organic MISM and MISIM (M = metal, I = insulator, S = semiconductor) devices, which effectively generate photo-induced displacement current and exhibit ferroelectric behavior. In previous studies, the S layer consisted of an organic donor-acceptor (DA) bilayer. In the present research, we fabricated MISM and MISIM devices using DA-type single-component molecules as the S layer and examined their photocurrent and polarization hysteresis. While the performance of these devices does not surpass that of DA bilayer devices, we discovered that DA-type single-component molecules can be utilized for photoelectric conversion and polarization trapping.

A triad molecular conductor: simultaneous control of charge and molecular arrangements.

Molecular and charge arrangements in the solid state were controlled by a new building block: a triad molecule. Owing to the appropriate flexibilities in both molecular structure and electron distribution of the triad, the apparently simple salt exhibits an unstable metallic phase, which is promising for superconducting transitions.

Improvement in Cycle Life of Organic Lithium-Ion Batteries by In-Cell Polymerization of Tetrathiafulvalene-Based Electrode Materials.

Redox-active organic molecules are promising candidates for next-generation electrode materials. Nevertheless, finding low-molecular-weight organic materials with a long cycle life remains a crucial challenge. Herein, we demonstrate the application of tetrathiafulvalene and its vinyl analogue bearing triphenylamines as long-cycle-life electrodes for lithium-ion batteries (LIBs). These molecules were successfully synthesized using palladium-catalyzed C-H arylation. Electrochemical analysis revealed that a polymer formed on the electrode. LIBs comprising these molecules exhibited noteworthy charge-discharge properties with a long cycle life (the capacity after 100 cycles was greater than 90% of the discharge capacity in the third cycle) and a high utilization ratio (approximately 100%). "In-cell" polymerization during the first charge process is considered to contribute to the effect. This study indicates new avenues for the creation of organic materials for rechargeable batteries.

Organic Molecular Conductors Based on Tetramethyl-TTP: Structural and Electrical Properties Modulated by the Anion Size and Shape.

The tetramethyl derivative of bis-fused tetrathiafulvalene, 2,5-bis(4,5-dimethyl-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (TMTTP), has been successfully synthesized. Most of the radical cation salts consisting of TMTTP feature a high electrical conductivity of σrt = 101 to 102 S cm-1 on a single crystal. The anion shape and size of TMTTP conductors modulate the electrical properties. The PF6- and AsF6- salts exhibit metallic conductivity down to 10 K, while the ReO4- and AuI2- salts show metal-to-insulator (MI) transition at 126 and 11 K, respectively. Single-crystal X-ray structure analysis of (TMTTP)2X (X = PF6, AsF6, BF4, and ReO4) and (TMTTP)3AuI2 reveals that the donor packing motif is categorized as the so-called ß-type. The tight-binding band calculations of (TMTTP)2X (X = ReO4, BF4, PF6, and AsF6) suggest these salts are characterized by quasi-one-dimensional Fermi surfaces. The band calculation based on X-ray structure analysis of (TMTTP)2ReO4 at 100 K demonstrates that the MI transition of this salt is associated with the charge ordering with the zigzag stripe pattern.

Synthesis, Structures, and Electronic Properties of 2,7-Anthrylene-Based Azacyclophanes Bearing o-, m-, and p-Phenylenediamine Linkers.

A series of novel azacyclophanes consisting of 2,7-anthrylene and phenylene units were designed and synthesized by the Buchwald-Hartwig coupling reaction to investigate their unique electronic properties in multiple oxidized states. Cyclic voltammetry showed that the p-phenylene derivative exhibited three reversible oxidation waves, whereas the o- and m-phenylene derivatives showed two quasi-reversible oxidation waves due to the complicated intramolecular interaction between the oxidized units and neutral units. Moreover, the absorption spectra of the p-phenylene derivative in different oxidation states showed absorption bands at 865 and 1025 nm, which were attributed to intramolecular charge-transfer interactions. The photophysical and electrochemical properties of the p-phenylene analog were also compared with those of the o- and m-phenylene derivatives based on theoretical calculations for further evaluation of the intramolecular electronic interactions.

Periphery Modification of Tetrathiafulvalenes: Recent Development and Applications.

Tetrathiafulvalene (TTF) and its analogs are fascinating molecules in materials science based on their excellent electron-donating abilities. This personal account describes recent advances in the synthesis of TTF analogs for functional materials via the palladium-catalyzed modification of peripheries of TTF analogs. We first consider three types of molecules: fluorophore-TTF hybrid molecules, multi-redox systems, and an organic ligand for metal-organic frameworks. These molecules were successfully synthesized via Stille coupling or palladium-catalyzed direct C-H arylation and their structural, electrochemical, and optical properties were clarified. Subsequently, phosphorus-substituted TTF analogs were successfully synthesized for future applications of redox-active phosphine ligands for metal catalysts. The development of these molecules can significantly affect the advancement of chemical science.

Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes.

Novel multistage redox tetrathiafulvalenes (TTFs) bearing 6-aryl-1,4-dithiafulvene moieties were synthesized by palladium-catalyzed direct C-H arylation. In the presence of a catalytic amount of Pd(OAc)2, P(t-Bu3)·HBF4, and an excess of Cs2CO3, the C-H arylation of TTF with several aryl bromides bearing 1,3-dithiol-2-ylidenes took place efficiently to produce the corresponding π-conjugated molecules. We also succeeded in the estimation of the oxidation potentials and number of electrons involved in each oxidation step of the obtained compounds by digital simulations.

Fused Tetrathiafulvalene and Benzoquinone Triads: Organic Positive-Electrode Materials Based on a Dual Redox System.

Fused donor-acceptor triads composed of two tetrathiafulvalenes (TTFs) and benzoquinone (BQ; 1) or naphthoquinone (NQ; 2) were successfully synthesized. X-ray structure analysis of the bis(n-butylthio) derivative revealed that the molecules are stacked in a head-to-tail manner. The bis(n-hexylthio)-1 exhibited six-pairs of one-electron transfer waves in the cyclic voltammogram, corresponding to the formation of both reduction and oxidation states from -2 to +4. The unsubstituted and bis(methylthio) derivatives of 1 and 2 were active materials in positive electrodes for rechargeable batteries, several of which displayed energy densities exceeding 800 mWh g-1 . The bis(methylthio)-2 also functions as a positive electrode material for a rechargeable sodium-ion battery.

A molecular crystal with an unprecedentedly long-lived photoexcited state.

The Au(iii)-complex anions in a newly synthesised compound BPY[Au(dmit)2]2 (BPY = N,N'-ethylene-2,2'-bipyridinium, dmit = 1,3-dithiole-2-thione-4,5-dithiolate) reversibly exhibit a molecular distortion in the solid state under UV-radiation. The photoexcited state is maintained for a week at 298 K, during which time molecules relax to their original structures and energy is gradually released as heat without decomposition or light emission. Most Au atoms adopt square planar (SP) coordination geometries, but some anions have unusual non-planar (NP) coordination geometries that produce disorder at the Au sites. The total (Gibbs) energy of the system depends on the proportion of Au atoms of NP geometry, which is directly determined from the occupancy (Occ (%)) by X-ray diffractometry. Due to phase transition, Occ substantially changes at a critical temperature (TC) of ∼280 K without other structural changes; however it remains almost constant in each phase. In addition, due to UV-promoted charge-transfer transitions between BPY and Au(dmit)2, Occ can be controlled by UV irradiation (∼250-450 nm). The UV-excited states have unprecedentedly long relaxation times (t1/2 > 36 h at 298 K), which is attributed to the close connection between the degrees of freedom on charge, spin, and molecular structures.

Hydration of Polycationic [5]Radialene with Quintuple 1,3-Dithiol-2-ylidenes Leads to a New Class of π-Extended Tetrathiafulvalene Scaffold.

[5]Radialene with quintuple 4,5-benzo-1,3-dithiol-2-ylidenes (DTs) easily forms a stable polycationic salt (1)4+ (BF4 - )4 owing to its aromatic character in the central cyclopentadienide ring. In this work, it was found that the polycationic salt (1)4+ underwent a hydration reaction in moist polar solvent to give several unexpected products, namely, an oxygen adduct dicationic salt (2)2+ , a tetrathiafulvalene (TTF) vinylogue (3) with 1,4-dithiine-2(3H)-one moieties, and an oxygen adduct of π-extended TTF with a cyclopentenone core (4). Their molecular structures were fully determined by X-ray crystal-structure analysis. In this reaction, irreversible hydration to the polycationic salt might either initiate the ring expansion and lead to the successive hydration at the specific cationic DT ring (for 3), or promote the transannular reactions to the next DT ring followed by elimination of the DT ring (for 4). Cyclic voltammetry and differential pulse voltammetry measurements for compound 3 indicated the occurrence of multi redox process resulting from electronic delocalization on the vinylogous TTF moiety. The electronic structures of the cationic species of 3 were also investigated by electronic spectra.

Redox-Switchable Bis-fused Tetrathiafulvalene Analogue: Observation and Control of Two Different Reduction Processes from Dication to Neutral State.

Derivatives of a new bis-fused donor composed of TTF and extended TTF with an anthraquinoid spacer (TTFAQ) (2) were successfully synthesized. X-ray structure analysis of the tetrakis(methylthio) derivative 2Aa and its I3- salt revealed that the TTFAQ moieties of both 2Aa and 2Aa•+ adopt the so-called saddle conformation similar to most neutral TTFAQs. The results obtained from the X-ray structure analysis and cyclic voltammetry suggest that a positive charge in 2Aa•+ is unevenly distributed on the TTF moiety, while both positive charges of 22+ are mainly located on the TTFAQ moiety. In the first two-electron redox processes, an extra cathodic wave attributed to the coexistence of a different reduction process from the oxidation process was observed for most of the derivatives.

Bis- and Tris-fused Tetrathiafulvalenes Extended with Anthracene-9,10-diylidene.

Bis- and tris-fused π-electron donors composed of extended tetrathiafulvalene with anthraquinoid spacers (4 and 5) were successfully synthesized. X-ray structure analysis of tetrakis(methylthio)-5 (5a) revealed that the molecule adopted a transoid-cisoid conformation. The cyclic voltammogram of 4a is composed of two pairs of two-electron redox waves, while the cyclic voltammogram of tetrakis(hexylthio) derivative 5b consists of one pair of four-electron redox waves and one pair of two-electron redox waves, respectively. Spectroelectrochemistry of 4a and 1H NMR spectrum of a 4b salt revealed that two positive charges in 42+ are distributed mainly on one TTFAQ (9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene) moiety.

Synthesis, Structure, Optical, and Electrochemical Properties of Triple- and Quadruple-Decker Co-facial Tetrathiafulvalene Arrays.

Understanding the details of the electronic structure in face-to-face arranged tetrathiafulvalenes (TTFs) is very important for the design of supramolecular functional materials and superior conductive organic materials. This article is a comprehensive study of the interactions among columnar stacked TTFs using trimeric (trimer) and tetrameric (tetramer) TTFs linked by alkylenedithio groups (-S(CH2 )n S-, n=1-4) as models of triple- and quadruple-decker TTF arrays. Single-crystal X-ray analyses of neutral trimeric TTFs revealed that the three TTF moieties are oriented in a zigzag arrangement. Cyclic voltammetry measurements (CV) reveal that the trimer and tetramer exhibited diverse reversible redox processes with multi-electron transfers, depending on the length of the -S(CH2 )n S- units and substituents. The electronic spectra of the radical cations, prepared by electrochemical oxidation, showed charge resonance (CR) bands in the NIR/IR region (1630-1850 nm), attributed to a mixed valence (MV) state of the triple- and quadruple-decker TTF arrays. In the trimeric systems, the dicationic state (+2; 0.66 cation per TTF unit) was found to be a stable state, whereas the monocationic state (+1) was not observed in the electronic spectra. In the tetrameric system, substituent-dependent redox processes were observed. Moreover, π-trimers and π-tetramers, which show a significant Davydov blueshift in the spectra, are formed in the tricationic (trimer) and tetracationic (tetramer) state. In addition, these attractive interactions are strongly dependent on the length of the linkage unit.

New tris- and pentakis-fused donors containing extended tetrathiafulvalenes: New positive electrode materials for rechargeable batteries.

Derivatives of tris-fused TTF extended with two ethanediylidenes (5), tris- and pentakis-fused TTFs extended with two thiophene-2,5-diylidenes (6-9) were successfully synthesized. Cyclic voltammograms of the tetrakis(n-hexylthio) derivative of 5 and 7 (5d, 7d) consisted of two pairs of two-electron redox waves and two pairs of one-electron redox waves. On the other hand, four pairs of two-electron redox waves and two pairs of one-electron redox waves were observed for the tetrakis(n-hexylthio) derivative of 9 (9d). Coin-type cells using the bis(ethylenedithio) derivatives of 5 (5b), 6 (6b) and the tetrakis(methylthio) derivatives of 5 (5c) and 8 (8c) as positive electrode materials showed initial discharge capacities of 157-190 mAh g(-1) and initial energy densities of 535-680 mAh g(-1). The discharge capacities after 40 cycles were 64-86% of the initial discharge capacities.

A stable metallic state of (TTPCOO)2NH4 with a mobile dopant.

Ammonium tetrathiapentalene carboxylate [(TTPCOO)2NH4] was prepared via protonic defect-induction doping without electrochemical oxidation. The high electric conductivity of 13 S cm(-1) and Pauli paramagnetic-like behavior of magnetic susceptibility in a wide temperature range exhibit a melting of the charge degrees of freedom induced by a mobile dopant in a salt bridge. Solid-state (1)H NMR strongly indicates a stable metallic state of this compound down to 4 K.

[5]Radialene-fused tetrathiafulvalenes exhibiting a simultaneous four- or eight-electron transfer.

Novel bis- and tris-fused tetrathiafulvalene (TTF) analogs possessing [5]radialene with quintuple 1,3-dithiol-2-ylidene moieties (2-4) were successfully synthesized. Cyclic voltammetry and differential pulse voltammetry revealed that they exhibited a simultaneous four- or eight-electron transfer process. It is suggested that four positive charges are distributed mainly over each of one or two DT[5]radialene units in 2(4+), 3(4+), and 4(8+).

Structural transitions from triangular to square molecular arrangements in the quasi-one-dimensional molecular conductors (DMEDO-TTF)2XF6 (X = P, As, and Sb).

A series of quasi-one-dimensional molecular conductors (DMEDO-TTF)(2)XF(6) (X = P, As, and Sb), where DMEDO-TTF is dimethyl(ethylenedioxy)tetrathiafulvalene, undergo characteristic structural transitions in the range of 130-195 K for the PF(6) salt and 222-242 K for the AsF(6) salt. The dramatic structural transition is induced by the order of the ethylenedioxy moiety, and the resulting anion rotation leads to the reconstruction of the H···F interaction between the methyl groups and the anions. The unique hydrogen bonds play a crucial role in the transition. As a result, the molecular packing is rearranged entirely; the high-temperature molecular stacks with an ordinary quasi-triangular molecular network transforms to a quasi-square-like network, which has never been observed among organic conductors. Nonetheless, the low-temperature phase exhibits a good metallic conductivity as well, so the transition is a metal-metal (MM) transition. The resistivity measured along the perpendicular direction to the conducting ac-plane (ρ(⊥)) and the calculation of the Fermi surface demonstrate that the high-temperature metal phase is a one-dimensional metal, whereas the low-temperature metal phase has considerable interchain interaction. In the SbF(6) salt, a similar structural transition takes place around 370 K, so that the quasi-square-like lattice is realized even at room temperature. Despite the largely different MM transition temperatures, all these salts undergo metal-insulator (MI) transitions approximately at the same temperature of 50 K. The low-temperature insulator phase is nonmagnetic, and the reflectance spectra suggest the presence of charge disproportionation with small charge difference (0.14).

Dimeric and trimeric tetrathiafulvalenes with strong intramolecular interactions in the oxidized states.

New dimeric and trimeric TTF derivatives with methylenedithio spacers (1a,b, 2a, and 2b) have been synthesized. X-ray structure analysis revealed that TTF units of the dimer 1b adopted distorted face-to-face overlapping arrangement both in intra- and intermolecular stacking. Cyclic voltammetric study indicated that trimeric 2a was in favor of taking di- and tetracationic states, while the dimeric 1a was in favor of taking a monocation. The absorption spectroscopic study suggested an existence of the strong face-to-face interaction particularly in di-, tri-, and tetracationic state of the trimeric TTF derivatives.

Tetrathiapentalene-based organic conductors.

The synthesis, structure and properties of tetrathiapentalene-based (TTP) organic conductors are reviewed. Among various TTP-type donors, bis-fused tetrathiafulvalene, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and its derivatives afford many metallic radical cation salts stable down to low temperatures, regardless of the size and shape of the counter anions. Most BDT-TTP conductors have a ß-type donor arrangement with almost uniform stacks. Introduction of appropriate substituents results in molecular packing that differs from the ß-type. A vinylogous TTP, 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (DTEDT) has yielded an organic superconductor (DTEDT)3Au(CN)2 as well as metallic radical cation salts, regardless of the counter anions. (Thio)pyran analogs of TTP, namely (T)PDT-TTP and its derivatives produce molecular conductors with novel molecular arrangements. A TTP analog with reduced π-electron system 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) has afforded several organic superconductors. Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)2 (M = Ni, Au).

Modulating the framework negative charge density in the system [BDT-TTP*+]/[Re6S5Cl9(1-)]/[Re6(S/Se)6Cl8(2-)]/[Re6S7Cl7(3-)]: templating by isosteric cluster anions of identical symmetry and shape, variations of incommensurate band filling, and electronic structure in 2D metals.

A series of 2D metals, beta-(BDT-TTP)6[Re6Se6Cl8] x (CHCl2-CHCl2)2, 2; beta-(ST-TTP)6[Re6S6Cl8] x (CH2Cl-CHCl2)2, 3; beta-(BDT-TTP)7[Re6S6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 4; beta-(BDT-TTP)7[Re6Se6Cl8]0.5[Re6S7Cl7]0.5 x (CH2Cl2), 5; beta-(BDT-TTP)8[Re6S7Cl7] x (CH2Cl2)4, 6 (BDT-TTP and ST-TTP are 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single beta-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic-neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)2[Re6S5Cl9], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2-6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic-inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-TTP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov-de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface.