Triadic Intramolecular Charge Transfer Compound of Tetrathiafulvalene Exhibiting Multicolor Solvatochromism

Development of a novel colorimetric thermometer based on poly(N-vinylcaprolactam) with push–π–pull tricyanofuran hydrazone anion dye

Thermochromic poly(N-vinylcaprolactam-co-tricyanofuran hydrazone) [poly(VC-co-TCFH)] gel labeled with a halochromic chromophore was developed using traditional free radical polymerization.

Reversible single crystal-to-single crystal double [2+2] cycloaddition induces multifunctional photo-mechano-electrochemical properties in framework materials

Reversible structural transformations of porous coordination frameworks in response to external stimuli such as light, electrical potential, guest inclusion or pressure, amongst others, have been the subject of intense interest for applications in sensing, switching and molecular separations. Here we report a coordination framework based on an electroactive tetrathiafulvalene exhibiting a reversible single crystal-to-single crystal double [2 + 2] photocyclisation, leading to profound differences in the electrochemical, optical and mechanical properties of the material upon light irradiation. Electrochemical and in situ spectroelectrochemical measurements, in combination with in situ light-irradiated Raman spectroscopy and atomic force microscopy, revealed the variable mechanical properties of the framework that were supported using Density Functional Theory calculations. The reversible structural transformation points towards a plethora of potential applications for coordination frameworks in photo-mechanical and photoelectrochemical devices, such as light-driven actuators and photo-valves for targeted drug delivery.

Porous coordination frameworks that undergo reversible structural transformations are promising for sensing, switching and separations. Here, the authors report an electroactive framework that exhibits a reversible single crystal-to-single crystal double [2+2] photocyclisation, leading to property changes.

Solvatochromic fluorescence properties of phenothiazine-based dyes involving thiazolo[4,5-b]quinoxaline and benzo[e]indole as strong acceptors

The present work describes the photophysical properties of two newly synthesized compounds, namely (E)-10-butyl-3-(2-(thiazolo[4,5-b]quinoxalin-2-yl)vinyl)-10H-phenothiazine (PTQ) and (E)-10-butyl-3-(2-(1,1-dimethyl-1H-benzo[e]indol-2-yl)vinyl)-10H-phenothiazine (PBI). A strong intramolecular charge transfer (ICT) is observed in both dyes as indicated from absorption and emission studies on varying the solvent polarity. This can be concluded from the large Stokes shifts among these dyes as PTQ exhibits large Stokes shift with >270nm and PBI around 200nm. The effect of increasing polarity caused drastic increase in the charge transfer process leading to twisted intramolecular charge transfer (TICT) process in both the dyes PTQ and PBI. Time-resolved emission studies and non-radiative decay rate constant indicates that the excited states of both dyes behave differently with respect to solvent polarity. The non-radiative decay constant increases dramatically with the solvent polarity specifying change of ICT emissive states in non-polar solvent while TICT emitting states in highly polar solvent. On the other hand, PBI follows a general trend initially exhibiting higher non-radiative decay constant in non-polar solvent like cyclohexane, lowest in moderate polarity owing to the ICT emissive state but with increase in the polarity, the non-radiative decay constant again increases indicating TICT states.

Alkali base triggered intramolecular charge transfer metallogels based on symmetrical A-π-D-chiral-D-π-A type ligands

Three l-tartaric acid based symmetrical A-π-D-chiral-D-π-A type structural isomeric nitrobenzylidenes (1-3) have been synthesized with intent to achieve isomer specific metallogels with intramolecular charge transfer properties. Alkali metal ions in these systems not only trigger charge transfer but also play a vital role in gelation. The presence of intramolecular rather than intermolecular charge transfer as well as aggregation has been well established by various kinds of experiments using UV-vis, CD, (1)H NMR, DFT and crystallography techniques. The role of alkali metal ions in triggering ICT was proved by titration with their respective crown ethers. Notably, Na(+) afforded twisted fiber morphology whilst Li(+) gave merely long range fibers. The true gel phase material was proved by detailed rheological studies.

Covalent non-fused tetrathiafulvalene–acceptor systems

The main families of non-fused TTF–acceptors are discussed with a special focus on their characteristics and properties.

An ionic charge-transfer dyad prepared cost-effectively from a tetrathiafulvalene carboxylate anion and a TMPyP cation

The assembly of a simple ionic supramolecular system would be a cost-effective way to construct donor–acceptor ensembles and the strong anion–cation interaction can enhance the charge-transfer between them.

Donor-acceptor type co-crystals of arylthio-substituted tetrathiafulvalenes and fullerenes

A series of donor-acceptor type co-crystals of fullerene (as the acceptor) and arylthio-substituted tetrathiafulvalene derivatives (Ar-S-TTF, as the donor) were prepared and their structural features were thoroughly investigated. The formation of co-crystals relies on the flexibility of Ar-S-TTF and the size matches between Ar-S-TTF and fullerene. Regarding their compositions, the studied co-crystals can be divided into two types, where types I and II have donor:acceptor ratios of 1:1 and 1:2, respectively. Multiple intermolecular interactions are observed between the donor and acceptor, which act to stabilize the structures of the resulting co-crystals. In the type I co-crystals, the fullerene molecule is surrounded by four Ar-S-TTF molecules, that is, two Ar-S-TTF molecules form a sandwich structure with one fullerene molecule and the other two Ar-S-TTF molecules interact with the fullerene molecule along their lateral axes. In the type II co-crystals, one fullerene molecule has the donor-acceptor mode similar to that in type I, whereas the other fullerene molecule is substantially surrounded by the aryl groups on Ar-S-TTF molecules and the solvent molecules.

Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives

Stille and Sonogashira coupling strategies allowed the preparation of luminescent TTF-benzothiadiazole donor–acceptor compounds with direct linkage or an acetylenic spacer.

Decorating tetrathiafulvalene (TTF) with fluorinated phenyls through sulfur bridges: facile synthesis, properties, and aggregation through fluorine interactions

Tetrathiafulvalene derivatives (TTF1-TTF9) bearing fluorinated phenyl groups attached through the sulfur bridges have been synthesized by employing a copper-mediated C-S coupling reaction of C6 H5-x Fx I (x=1, 2, 5) and a zinc-thiolate complex, (TBA)2 [Zn(DMIT)2 ] (TBA=tetrabutyl ammonium, DMIT=1,3-dithiole-2-thione-4,5-dithiolate), as the key step. Particularly, the selective synthesis of C6 F5 -substituted (TTF8) and C6 F4 -fused (TTF9) TTFs from C6 F5 I is disclosed. The physicochemical properties and crystal structures of these TTFs are fully investigated by UV/Vis absorption spectra, cyclic voltammetry, molecular orbital calculation, and single-crystal X-ray diffraction. The exchange of hydrogen versus fluorine on the peripheral phenyl groups show a notable influence on both the electronic and crystallographic natures of the resulting TTFs: 1) lowering both the HOMO and the LUMO energy levels, 2) modulating the electrochemical properties by regioselective and/or the degree of fluorination, 3) enhancing the driving forces of stacking by multiple fluorine interactions (F⋅⋅⋅S, CF⋅⋅⋅π/πF , CF⋅⋅⋅FC, and CF⋅⋅⋅H). This work indicates that the decoration with fluorinated phenyls holds promise to produce functional TTFs with novel electronic and aggregation features.

Metal centered oxidation or ligand centered oxidation of metal dithiolene? Spectral, electrochemical and structural studies on a nickel-4-pyridine-1,2-dithiolate system

The complex Et(4)N[Ni(4-pedt)(2)] (1) (4-pedt = 1-(pyridine-4-yl) ethylene-1,2-dithiolate) was synthesized to investigate the behaviour of metal dithiolene compounds upon protonation and oxidation by absorption spectroscopy, electrochemistry and structural analyses and to further understand the electronic states of the dithiolene compounds. It is unexpected that the 915 nm NIR transition band is not shifted when H(+) is added, and it is only affected (blue-shifted) when the compound is oxidized. All the evidence of electronic spectra indicates that the NIR band is relevant to the central [Ni(edt)(2)] moiety (edt = ethylenedithiolate), not the behaviour of individual Ni ions or ligands. It is also not the band of intermolecular interaction of a dimer. The moderately intense band appearing at 655 nm upon protonation is assigned to the intramolecular charge-transfer band between the [Ni(edt)(2)] moiety and the pyridine. The redox potentials of the metal dithiolene are sensitive to the protonation of the pyridyl group. The structures of monocationic complex and the protonated compounds [Ni(4-Hpedt)(2)]·ClO(4)·H(2)O (2) and [Ni(4-Hpedt)(2)]·PhSO(3)·2DMF (3) were characterized by single crystal X-ray determination. The structural data demonstrate that the oxidation of the monoanionic dithiolene complex to neutral does not change the Ni-S bond distances obviously, which further indicates that the process is not only the metal centered oxidation.