Metal–organic frameworks (MOFs) have aroused great interest as lithium-ion battery (LIB) electrode materials. In this work, we first report that a pristine three-dimensional tetrathiafulvalene derivatives (TTFs)-based zinc MOF, formulated [Zn2(py-TTF-py)2(BDC)2]·2DMF·H2O (1) (py-TTF-py = 2,6-bis­(4′-pyridyl)­tetrathiafulvalene and H2BDC = terephthalic acid), can work as a high-performance electrode material for rechargeable LIBs. The TTFs-Zn-MOF 1 electrode displayed a high discharge specific capacity of 1117.4 mA h g–1 at a current density of 200 mA g–1 after 150 cycles along with good reversibility. After undergoing elevated discharging/charging rates, the electrode showed superior lithium storage performance in the extreme case of 20 A g–1 and could finally recover the capability when the current rate was back to 200 mA g–1. Particularly, specific capacities of 884.2, 513.8, and 327.8 mA h g–1 were reached at high current densities of 5, 10, and 20 A g–1 after 180, 175, and 300 cycles along with good reversibility, respectively. Such an excellent performance is first reported for the LIB anode materials. TTFs-Zn-MOF 2, namely, [Zn2(py-TTF-py) (BDC)2]·DMF·2H2O (2), was prepared as a contrast to explore the relationship between the structures of the electrode materials and the electrochemical properties. Based on the structural analysis of 1 and 2 and ex situ X-ray photoelectron spectroscopy, the TTF moiety and the twofold TTF pillar play a key role in the excellent electrochemical performance. The full cell of MOF 1 with NMC 622 delivered the capacity of 131.9 mA h g–1 at 100 mA g–1 with the Coulombic efficiency of 99.45% after 70 cycles and exhibited the tolerance to high-current operation.

Titanium oxo clusters (TOCs) have become one of the worldwide hot research topics because they are excellent molecular TiO materials having unique photoactive properties and can been used as models of dye-sensitized solar cells (DSSCs). S-Heterocyclic ligands such as thiophene (Th) and tetrathiafulvalene (TTF) derivatives have been widely used in electronic or photoelectronic devices and solar cells. However, a study of the synthesis and properties of TOCs anchored with Th and TTF derivatives is missing. Herein four such TOCs as single crystals were synthesized and structurally c h a r a c t e r i z e d :(3), and [Ti 6 O 4 (O i Pr) 10 (L TTF ) 2 (O 3 PPh) 2 ] (4). Charge transfer from the Th or TTF electron donor to the TOC core was evaluated by electronic spectra and theoretical calculations. This work first systematically investigated the photoelectrochemistry of TOCs with different conjugated S-heterocyclic ligands in molecular levels. The photocurrent densities of these clustermodified TiO 2 electrodes were examined using DSSCs, which were well responsive to irradiation. The photocurrents of TTF cluster-modified electrodes are higher than those of the Th cluster-modified electrodes because of the sulfur-rich conjugated system.

Tetrathiafulvalene (TTF) derivatives as promising hole transport materials in assembling hybrid halide perovskite solar cells have attracted great attention; however, electron transfer or charge-transfer (CT) between TTF and metal halides has been studied with less detail at the molecular level. Using molecular models, we herein report four new TTF-bismuth-halides assembled by methylated or protonated bis(4'-pyridyl)-tetrathiafulvalene cations, (MePy)TTF or (HPy)TTF, and bismuth-halide anions. Single crystal analysis showed that the cations are stacked to form a TTF column, and the bismuth-halide anions are inlaid between the TTF columns with anion-cation interactions. In these compounds, the main contribution to CT is the intracation CT, namely intramolecular CT (IMCT) from TTF moiety to pyridinium group. However, the anion to cation CT (ACCT) has a significant effect on the IMCT and physical properties. The different anion-cation interaction modes result in different synergistic effects of IMCT and ACCT, which modified the band gaps and photocurrent properties of the hybrids. The research gives a clear image of structure-property relationship and provides a perspective on the design of new perovskite materials at the molecular level.

Understanding the effect of charge transfer on the physical properties of metal–organic frameworks (MOFs) is essential for designing multifunctional MOF materials. In this work, three redox-active tetrathiafulvalene (TTF)-based MOFs, formulated as [Co6L6(bpe)6(EtOH)2(MeOH)2(H2O)] n ·5nH2O (1), [Co5(μ3–OH)2L4(bpe)2] n (2), and [CoL­(bpa)­(H2O)] n ·2nH2O (3) (L = dimethylthio-tetrathiafulvalene-bicarboxylate, bpe = 1,2-bis­(4-pyridyl)­ethene, bpa = 1,2-bis­(4-pyridyl)­ethane), are crystallographically characterized. Complexes 1 and 3 are two-dimensional (2D) coordination polymers, and 2 features an unusual three-dimensional (3D) MOF. The structure of 2 contains a cluster chain constructed from μ2-O bridged pentanuclear cluster subunits, which is first found for 3D MOFs. Complexes 1 and 2 are comprised of the same ligands L and bpe but with different multidimensional configuration, and complexes 1 and 3 have the same 2D layered structures with the same ligand L but with different conjugation ligand bpe/bpa, which provide a good comparison for the structure–property relationship. The charge-transfer (CT) interactions within MOF 1 are stronger than those of 2 due to the closer packing of electron donor (D) L and electron acceptor (A) bpe in 1, and no CT occurs within MOF 3 because of the unconjugated bpa. The order of photocurrent density is 1 > 2 ≫ 3, which is in accordance with that of CT interactions. Further analysis reveals that the CT interactions within the MOF are not beneficial for the supercapacitance which is verified by the highest supercapacitance performance of 3. This work is the first study of the structures and CT effects on the supercapacitance performance.

Although pristine metal–organic framework (MOF) anodes for lithium-ion batteries (LIBs) show moderate activities and relatively stable cycling, the poor rate capability of the MOF anodes limited their applications in the development of a new generation of energy storage. Herein, the electric active CoII ion is selected to coordinate with redox-active S-rich tetrathiafulvalene (TTF) derivatives to create two TTF-Co-MOFs, formulated as [Co2(py-TTF-py)2(BDC)2]·2DMF·H2O (TTF-Co-MOF 1) and [Co2(py-TTF-py)2(BPDC)2]·3DMF·3H2O (TTF-Co-MOF 2), where py-TTF-py = 2,6-bis­(4′-pyridyl)­tetrathiafulvalene, H2BDC = terephthalic acid, H2BPDC = biphenyl-4,4′-dicarboxylic acid, and DMF = N,N-dimethylformamide. Crystallographic characterization indicated that the two MOFs possess similar 2-fold-interpenetrating 3D frameworks but with two different pore sizes. The pore-size-dependent performances of the TTF-Co-MOFs were explored to optimize the MOFs as the anode materials for LIBs. TTF-Co-MOF 1 presents a high reversible specific capacity of 1186.6 mAh g–1 at 200 mA g–1 after 287 cycles. The rate capability is greatly enhanced by the introduction of CoII into TTF-based MOFs with specific capacities of 1028.6 mAh g–1 at 5 A g–1 and 966.5 mAh g–1 at 10 A g–1. On the basis of the series analysis of theoretical calculations, electrochemical impedance spectroscopy, and crystal structures, it is found that the CoII metal centers play a bridging role in charge transport within the MOF framework, which is beneficial for the transportation of Li ions. The competitive performances of TTF-Co-MOF 1 are attributed to the synergistic effect of the CoII metal centers and S-rich TTF ligand as well as suitable porosity. The study shed some light for the fabrication of advanced energy storage devices through the rational design of MOF-based anode materials.