Tetrathiafulvalene- (TTF-) Derived Oligopyrrolic Macrocycles

Organic Donor-Acceptor Complexes As Potential Semiconducting Materials

In this review article, the synthesis, characterization and physico-chemical properties of the organic donor-acceptor complexes are highlighted and a special emphasis has been placed on developing them as semiconducting materials. The electron-rich molecules, i. e., donors have been broadly grouped in three categories, namely polycyclic aromatic hydrocarbons, nitrogen heterocycles and sulphur containing aromatic donors. The reactions of these classes of the donors with the acceptors, namely tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), tetracyanobenzene (TCNB), benzoquinone, pyromellitic dianhydride and pyromellitic diimides, fullerenes, phenazine, benzothiadiazole, naphthalimide, DMAD, maleic anhydride, viologens and naphthalene diimide are described. The potential applications of the resulting DA complexes for physico-electronic purposes are also included. The theoretical investigation of many of these products with a view to rationalise their observed physico-chemical properties is also discussed.

Extended Tetrathiafulvalenes with Fluoreno[3,2-b]fluorene and Diindeno[1,2-b : 1',2'-i]anthracene Cores

In one-dimensional polycyclic aromatic hydrocarbons (PAHs) containing five- and six-membered rings fused together, one key question is whether the structures possess a quinoidal or aromatic diradical character. Here, we generate such PAHs by reversible oxidation of PAH-extended tetrathiafulvalenes (TTFs). Extended TTFs were thus prepared and studied for their geometrical properties (crystallography), redox properties, and UV/Vis/NIR/EPR characteristics as a function of charge state. The EPR measurements of radical cations showed unique features for each PAH-TTF. The dications, formally composed of fluoreno[3,2-b]fluorene and diindeno[1,2-b:1',2'-i]anthracene cores, were experimentally found to exhibit singlet ground states. For the latter, calculations reveal the closed shell, quinoid singlet state to be isoenergetic with the open shell singlet diradical. Each charge state exhibited unique optical properties with radical cations absorbing strongly in the NIR region with signatures from π-dimers for the large core. The experimental results were paralleled and supported by detailed computations, including spin density distribution calculations, EPR simulations, and nucleus independent chemical shift (NICS) xy scans.

Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/enediyne acceptor units

Large donor-acceptor scaffolds derived from polycyclic aromatic hydrocarbons (PAHs) with tunable HOMO and LUMO energies are important for several applications, such as organic photovoltaics. Here, we present a large selection of PAHs based on central indenofluorene (IF) or fluorene cores and containing various dithiafulvene (DTF) donor units that gain aromaticity upon oxidation and a variety of acceptor units, such as vinylic diesters, enediynes, and cross-conjugated radiaannulenes (RAs) that gain aromaticity upon reduction. In some cases, the DTF units are expanded by pyrrolo annelation. The optical and redox properties of these compounds, in some cases carbon-rich, were studied by UV-vis absorption spectroscopy and cyclic voltammetry. Synthetically, the work explores IF diones or fluorenone as central building blocks by subjecting the carbonyl groups to a variety of reactions; that are, phosphite- or Lawesson's reagent-mediated olefination reactions (to introduce DTF motifs), Ramirez/Corey-Fuchs dibromo-olefinations followed by Sonogashira couplings (to introduce enediynes motifs), and Knoevenagel condensations (to introduce the vinylic diester motif). By a subsequent Glaser-Hay coupling reaction, a RA acceptor unit was introduced to provide a DTF-IF-RA donor-acceptor scaffold with a low-energy charge-transfer absorption and multi-redox behavior.

Synthesis of 2-(Methylthio)-1,3-dithioles from 1,3-Dithiole-2-thiones: Important Building Blocks in Tetrathiafulvalene Chemistry

2-(Methylthio)-1,3-dithioles are important heterocyclic compounds used for the preparation of redox-active derivatives of tetrathiafulvalene as they serve as precursors for phosphonate esters that can be employed in Horner-Wadsworth-Emmons olefination reactions. Here, we present a mild and less hazardous method than previous methods for converting readily accessible 1,3-dithiole-2-thiones into 2-(methylthio)-1,3-dithioles by methylation with trimethyl orthoformate and HBF4·Et2O and a subsequent reduction with NaBH4.

Synthesis and Properties of Norphthalocyanines Functionalized with a Tetrathiacrown Ether-Tetrathiafulvalene Substituent

To construct novel ion receptors and D-A self-assembly systems for materials with better functions, the annulation of a tetrathiafulvalene donor with a magnesium norphthalocyanine core via a flexible tetrathiacrown ether bridge afforded a new triad 1. The structure of this product was characterized by 1H NMR and infrared spectroscopy, time-of-flight mass spectrometry, and elemental analysis. The optical and electrochemical properties were investigated using UV-vis spectroscopy and cyclic voltammetry. The complex of triad 1 and 2,3,5,6- tetrafluoro-7,7,8,8-tetracyanoquinodimethane produced electron transfer with a radical cationic character, as confirmed by UV-Vis and electron paramagnetic resonance analysis. Furthermore, the target compound presented evident intramolecular charge-transfer interactions in ground states, which were explained using density functional theory. Furthermore, norphthalocyanine 1 was able to coordinate Ag⁺ through the peripheral ligating oxathiaether crown.

A Macrocyclic Furan with Accessible Oxidation States: Switching Between Aromatic and Antiaromatic Global Ring Currents

Macrocyclic furans are predicted to switch between global aromaticity and antiaromaticity, depending on their oxidation states. However, the macrocyclic furans reported to date are stabilized by electron withdrawing groups, which result in inaccessible oxidation states. To circumvent this problem, a post-macrocyclization approach was applied to introduce methylene-substituted macrocyclic furans, which display an extremely low oxidation potential of -0.23 vs. Fc/Fc⁺ , and are partially oxidized in ambient conditions. Additional oxidation to the dication results in aromaticity switching to a global 30πe^- aromatic state, as indicated by the formation of a strong diatropic current observed in the ¹ H NMR spectrum. NICS and ACID calculations support this trend and provide evidence for a different pathway for the global current in the neutral and dicationic states. According to these findings, macrocyclic furans can be rendered as promising p-type materials with stable oxidation states.

A bis-NHC-CAAC dimer derived dicationic diradical

The isolation of carbon-centered diradicals is always challenging due to synthetic difficulties and their limited stability. Herein we report the synthesis of a trans-1,4-cyclohexylene bridged bis-NHC-CAAC dimer derived thermally stable dicationic diradical. The diradical character of this compound was confirmed by EPR spectroscopy. The variable temperature EPR study suggests the singlet state to be marginally more stable than the triplet state (2J = -5.5 cm-1 (ΔE ST = 0.065 kJ mol-1)). The presence of the trans-1,4-cyclohexylene bridge is instrumental for the successful isolation of this dicationic diradical. Notably, in the case of ethylene or propylene bridged bis-NHC-CAAC dimers, the corresponding dicationic diradicals are transient and rearrange to hydrogen abstracted products.

Electron-Rich Diruthenium Complexes with π-Extended Alkenyl Ligands and Their F4 TCNQ Charge-Transfer Salts

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(Pⁱ Pr₃ )₂ (L)} entities (L=Cl^- in complexes Ru₂ -3 and Ru₂ -7; L=acetylacetonate (acac^- ) in complexes Ru₂ -4 and Ru₂ -8) and with π-conjugated 2,7-divinylphenanthrenediyl (Ru₂ -3, Ru₂ -4) or 5,8-divinylquinoxalinediyl (Ru₂ -7, Ru₂ -8) as bridging ligands are reported. The bridging ligands are laterally π-extended by anellating a pyrene (Ru₂ -7, Ru₂ -8) or a 6,7-benzoquinoxaline (Ru₂ -3, Ru₂ -4) π-perimeter. This was done with the hope that the open π-faces of the electron-rich complexes will foster association with planar electron acceptors via π-stacking. The dinuclear complexes were subjected to cyclic and square-wave voltammetry and were characterized in all accessible redox states by IR, UV/Vis/NIR and, where applicable, by EPR spectroscopy. These studies signified the one-electron oxidized forms of divinylphenylene-bridged complexes Ru₂ -7, Ru₂ -8 as intrinsically delocalized mixed-valent species, and those of complexes Ru₂ -3 and Ru₂ -4 with the longer divinylphenanthrenediyl linker as partially localized on the IR, yet delocalized on the EPR timescale. The more electron-rich acac^- congeners formed non-conductive 1 : 1 charge-transfer (CT) salts on treatment with the F₄ TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F₄ TCNQ^.- radical anions in these CT salts, but produced no firm evidence for the relevance of π-stacking to their formation and properties.

Charge-transfer regulated visible light driven photocatalytic H2 production and CO2 reduction in tetrathiafulvalene based coordination polymer gel

The much-needed renewable alternatives to fossil fuel can be achieved efficiently and sustainably by converting solar energy to fuels via hydrogen generation from water or CO₂ reduction. Herein, a soft processable metal-organic hybrid material is developed and studied for photocatalytic activity towards H₂ production and CO₂ reduction to CO and CH₄ under visible light as well as direct sunlight irradiation. A tetrapodal low molecular weight gelator (LMWG) is synthesized by integrating tetrathiafulvalene (TTF) and terpyridine (TPY) derivatives through amide linkages and results in TPY-TTF LMWG. The TPY-TTF LMWG acts as a linker, and self-assembly of this gelator molecules with Zn^II ions results in a coordination polymer gel (CPG); Zn-TPY-TTF. The Zn-TPY-TTF CPG shows high photocatalytic activity towards H₂ production (530 μmol g^-1h^-1) and CO₂ reduction to CO (438 μmol g^-1h^-1, selectivity > 99%) regulated by charge-transfer interactions. Furthermore, in situ stabilization of Pt nanoparticles on CPG (Pt@Zn-TPY-TTF) enhances H₂ evolution (14727 μmol g^-1h^-1). Importantly, Pt@Zn-TPY-TTF CPG produces CH₄ (292 μmol g^-1h^-1, selectivity > 97%) as CO₂ reduction product instead of CO. The real-time CO₂ reduction reaction is monitored by in situ DRIFT study, and the plausible mechanism is derived computationally.

Fullerene Wires Assembled Inside Carbon Nanohoops

Carbon-nanohoop structures featuring one or more round-shaped cavities represent ideal supramolecular hosts for spherical fullerenes, with potential to form host-guest complexes that perform as organic semiconductors in the solid state. Due to the tight complexation between the shape-complementary hosts and guests, carbon nanohoops have the potential to shield fullerenes from water and oxygen, known to perturb the electron-transport process. Many nanohoop receptors have been found to form host-guest complexes with fullerenes. However, there is only a little or no control over the long-range order of encapsulated fullerenes in the solid state. Consequently, the potential of these complexes to perform as organic semiconductors is rarely evaluated. Herein, we present a survey of all known nanohoop-fullerene complexes, for which the solid-state structures were obtained. We discuss and propose instances where the inclusion fullerene guests form discrete supramolecular wires, which might open up possibilities for their use in electronic devices.

Electrocatalytic Behavior of Tetrathiafulvalene (TTF) and Extended Tetrathiafulvalene (exTTF) [FeFe] Hydrogenase Mimics

TTF- and exTTF-containing [(μ-S₂)Fe₂(CO)₆] complexes have been prepared by the photochemical reaction of TTF or exTTF and [(μ-S₂)Fe₂(CO)₆]. These complexes are able to interact with PAHs. In the absence of air and in acid media an electrocatalytic dihydrogen evolution reaction (HER) occurs, similarly to analogous [(μ-S₂)Fe₂(CO)₆] complexes. However, in the presence of air, the TTF and exTTF organic moieties strongly influence the electrochemistry of these systems. The reported data may be valuable in the design of [FeFe] hydrogenase mimics able to combine the HER properties of the [FeFe] cores with the unique TTF properties.

Description of Sudden Polarization in the Excited Electronic States with an Ensemble Density Functional Theory Method

Sudden polarization (SP) is one of the manifestations of electron transfer in the electronically excited states of molecules. Proposed initially to explain the unusual reactivity of photoexcited olefins, SP often occurs in the excited states of molecules possessing strongly correlated diradical ground state. Theoretical description of SP involves mixing between the singly excited and the doubly excited zwitterionic states, which makes it inaccessible with the use of the popular linear-response time-dependent density functional theory methods. In this work, an extended variant of the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS, or SSR) method is applied to study SP in a number of organic diradical systems. To this end, the analytical derivative formalism is derived and implemented for the SSR(3,2) method (see the main text for explanation of the acronym), which enables the automatic geometry optimization and obtains the relaxed density matrices as well as the electron binding energies and respective Dyson's orbitals. Application of the new method to SP in the lowest singlet excited state of ethylene agrees with the results obtained previously with the use of multireference methods of wavefunction theory. A number of interesting manifestations of SP are observed, such as the charge transfer in photoexcited tetramethyleneethene (TME) diradical mediated by the vibrational motion and conductivity switching in the excited state of a donor-acceptor dyad placed in an external electric field.

The 1,3-dithiol-2-ide carbanion

1,3-Dithiol-2-ide is a fully unsaturated five-membered heterocycle with a carbanion unit between two of the ring sulfur atoms. Derivatives thereof are important intermediates in synthetic protocols for preparing various 1,4-dithiafulvene (DTF) and tetrathiafulvalene (TTF) compounds by Wittig, Horner-Wadsworth-Emmons, or phosphite-mediated olefination reactions. When considering the electronic properties of DTF, one would usually consider this unit as an electron-donating group as it can form a 6π-aromatic 1,3-dithiolium ring by resonance. Yet, in this review, I will move forward a dual character of the DTF by which it can also act as an electron-withdrawing group, involving formation of the 1,3-dithiol-2-ide. In particular, this electronic effect can be used to explain its ability to promote the electrocyclic ring closure of a vinylheptafulvene into a dihydroazulene. This view on the properties of DTF is very much in line with the dual reactivity of ketene dithioacetals that react with both nucleophiles and electrophiles. Moreover, the 1,3-dithiol-2-ide unit was recently generated in the reduction of an extended and quinoid-like TTF where the core became an aromatic carbo-benzene moiety. This aspect is particularly interesting for future design of extended TTFs that can act as both electron donors and acceptors.

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.

Benzo-Tetrathiafulvalene- (BTTF-) Annulated Expanded Porphyrins: Potential Next-Generation Multielectron Reservoirs

Two sterically crowded benzo-tetrathiafulvalene (BTTF)-annulated expanded porphyrins (BTTF7-F and BTTF8) are synthesized. Detailed photophysical investigations reveal their intrinsic intramolecular charge transfer (CT) character, originated from partial electron transfer from electron-rich TTF units to the relatively electron-deficient macrocyclic core. This finding stands in contrast to what was observed in the previously reported Figure-of-eight conformer of BTTF-annulated [28]hexaphyrin (BTTF6), in which a typical π-π* electronic transition from HOMO to LUMO was observed. However, core expansion in BTTF7-F and BTTF8 makes the oligopyrrole macrocyclic cores relatively more electron-deficient, facilitating the effective intramolecular CT process. Comparative electrochemical investigations reveal that the current generated at the oxidative region is directly proportional to the number of TTF units attached to the macrocyclic core. This work demonstrates the control of the intramolecular CT process through incremental addition of TTF units to the macrocyclic core. Facile multielectron electrochemical oxidations of these expanded porphyrins suggest that they behave like potential multielectron reservoirs.

Donor/acceptor substituted dithiafulvenes and tetrathiafulvalene vinylogues: electronic absorption, crystallographic, and computational analyses

The structural, electronic, and crystallographic properties of nitrophenyl and methoxyphenyl-substituted dithiafulvenes and tetrathiafulvalene vinylogues were systematically investigated by experimental and computational approaches.

Tuning the electronic and nonlinear optical properties of black phosphorus quantum dots by introducing electron-donating/withdrawing molecules (TTF/TCNQ)

Black phosphorous quantum dots can exhibit excellent nonlinear optical properties after adsorbing organic molecules (TTF and TCNQ).

The relationship between photophysical properties and aromaticity/antiaromaticity of various expanded porphyrins — a Hans Fischer Career Award paper

Understanding aromaticity is crucial for predicting the molecular properties and reactivity of cyclic [Formula: see text]-conjugated systems. In this review, representative reports on the evaluation of aromaticity via spectroscopic methods in various expanded porphyrin systems are presented. The relationship between the photophysical properties and distinct aromatic characteristics in Hückel aromatic compounds was revealed through notable spectroscopic features exhibited by aromatic expanded porphyrins. Furthermore, modulating the molecular conformation and chemical environment enabled us to distinguish unique Möbius aromatic molecules successfully. These findings provide insight into the elemental molecular properties and aromaticity in expanded porphyrin systems and their potential real-world applications.

Iterative Suzuki-Miyaura Cross-coupling/Bromo-desilylation Reaction Sequences for the Assembly of Chemically Well-defined, Acyclic Oligopyrrole/Benzenoid Hybrids Embodying Mixed Modes of Connectivity

Syntheses of a range of chemically well-defined oligopyrrole/benzenoid hybrids are described using tandem Suzuki-Miyaura cross-coupling/bromo-desilyation reaction sequences for linking borylated pyrroles, halogenated pyrroles and/or dibromobenzenes to one another. By such means, including iterative variants, a range of all α-linked, all β-linked oligopyrroles as well as certain combinations thereof have been assembled, some of them for the first time. The conductivities of iodine-treated thin films formed from certain such systems have been determined.

Redox-Responsive Host-Guest Chemistry of a Flexible Cage with Naphthalene Walls

"Naphthocage", a naphthalene-based organic cage, reveals very strong binding (up to 10¹⁰ M^-1) to aromatic (di)cationic guests, i.e., the tetrathiafulvalene mono- and dication and methyl viologen. Intercalation of the guests between two naphthalene walls is mediated by C-H···O, C-H···π, and cation···π interactions. The guests can be switched into and out of the cage by redox processes with high binding selectivity. Oxidation of the flexible cage itself in the absence of a guest leads to a stable radical cation with the oxidized naphthalene intercalated between and stabilized by the other two. Encapsulated guest cations are released from the cavity upon cage oxidation, paving the way to future applications in redox-controlled guest release or novel stimuli-responsive materials.

Gel Formed by Self-Assembly of a Urea-Modified Monopyrrolotetrathiafulvalene Derivative Displays Multi-Stimuli Responsiveness and Absorption of Rhodamine B

A new monopyrrolotetrathiafulvalene-based derivative containing a urea group was designed, synthesized and thoroughly characterized. It proved to be a non-gelator in a single solvent even when heated or sonicated. However, it could self-assemble in a CHCl₃ (CH₂ Cl₂ )/n-hexane mixture to form a thermo-responsive supramolecular organogel. SEM, FT-IR spectroscopy, UV/Vis absorption spectroscopy, and SAXS revealed that in the organogel system, the gelators self-assembled into supramolecular networks with a J-type aggregation mode under the joint effect of π-π stacking, intermolecular hydrogen-bonding, and van der Waals forces. Interestingly, the gel phase was shown to undergo reversible gel-sol transformation induced by Fe³⁺ -Vitamin C (Vc), trifluoroacetic acid-triethylamine (TFA-TEA) and picric acid (PA)-NaOH. In particular, in the presence of picric acid, the experimental results proposed that charge transfer occurred from the electron-donor gelator to the electron-acceptor picric acid due to the possibility of complex formation. Furthermore, the formed organogel could behave as the matrix for encapsulating cationic fluorescent dye from wastewater, and the adsorption efficiency was directly proportional to the concentration of the gelator.

Tuning Redox Properties and Self-Assembly of Thienoacene-Extended Tetrathiafulvalenes

Turning on and off associations between molecules by a reversible change in their redox states is a convenient way of controlling self-assembly and hence for advancing supramolecular chemistry. Here we present systematic studies on a selection of extended tetrathiafulvalenes with thienoacene spacers. By cyclic and differential pulse voltammetry and in situ EPR/UV-Vis-NIR spectroelectrochemistry, in combination with computations, we have elucidated how the number and orientations of thiophene rings in the spacer between the two dithiafulvene rings influence both the donor strength and association properties. The radical cations and their associates were found to cover a remarkable large region of the UV-Vis-NIR spectrum, but the appearance of the absorption spectrum of the radical cations as well as of the unassociated dications also depended strongly on the exact molecular structure.

Metalla-Assembled Electron-Rich Tweezers: Redox-Controlled Guest Release Through Supramolecular Dimerization

Developing methodologies for on-demand control of the release of a molecular guest requires the rational design of stimuli-responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination-tweezers has been less explored. Herein, we report the first example of a redox-triggered guest release from a metalla-assembled tweezer. This tweezer incorporates two redox-active panels constructed from the electron-rich 9-(1,3-dithiol-2-ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron-poor planar unit, forming a 1:1 host-guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox-triggered molecular delivery pathway.

Dimers of pyrrolo-annelated indenofluorene-extended tetrathiafulvalenes – large multiredox systems

A new pyrrolo-annelated indenofluorene-extended tetrathiafulvalene building block was developed and employed in N-arylation reactions for construction of redox-active dimeric scaffolds.

Chiroptical inversion of a planar chiral redox-switchable rotaxane

A tetrathiafulvalene (TTF)-containing crown ether macrocycle with C s symmetry was designed to implement planar chirality into a redox-active [2]rotaxane. The directionality of the macrocycle atom sequence together with the non-symmetric axle renders the corresponding [2]rotaxane mechanically planar chiral. Enantiomeric separation of the [2]rotaxane was achieved by chiral HPLC. The electrochemical properties - caused by the reversible oxidation of the TTF - are similar to a non-chiral control. Reversible inversion of the main band in the ECD spectra for the individual enantiomers was observed after oxidation. Experimental evidence, conformational analysis and DFT calculations of the neutral and doubly oxidised species indicate that mainly electronic effects of the oxidation are responsible for the chiroptical switching. This is the first electrochemically switchable rotaxane with a reversible inversion of the main ECD band.

One-dimensional single-helix coordination polymer self-assembled by a crown-ether appended-N-heteroacene radical anion

A crown-ether appended N-heteroacene 1 was reduced in the presence of NaBPh₄ to the radical anion 2 by accepting one electron transferred from both the cathode and BPh₄^- as a reductant. The obtained radical anion 2 can function as a radical anion ligand to bridge two sodium ions to self-assemble into one-dimensional helical coordination polymers.

Bis(1,3-dithiol-2-ylidene)-Substituted Subtriazachlorin: A Subphthalocyanine Analogue with Redox Properties

Bis(1,3-dithiol-2-ylidene)-substituted subtriazachlorin was formed because of an unusual reaction of a 1,3-dithiole-2-one-fused subphthalocyanine in a triethylphosphite-mediated tetrathiafulvalene synthesis. In this novel molecule, the bis(1,3-dithiol-2-ylidene)ethane moiety and subtriazachlorin structure are fused, resulting in an electron-donating ability and broad absorption in the near-infrared region.

Photoresponsive Porphyrin Nanotubes of Meso-tetra(4-Sulfonatophenyl)Porphyrin and Sn(IV) meso-tetra(4-pyridyl)porphyrin

Porphyrin macrocycles and their supramolecular nanoassemblies are being widely explored in energy harvesting, sensor development, catalysis, and medicine because of a good tunability of their light-induced charge separation and electron/energy transfer properties. In the present work, we prepared and studied photoresponsive porphyrin nanotubes formed by the self-assembly of meso-tetrakis(4-sulfonatophenyl)porphyrin and Sn(IV) meso-tetra(4-pyridyl)porphyrin. Scanning electron microscopy and transmission electron microscopy showed that these tubular nanostructures were hollow with open ends and their length was 0.4–0.8 μm, the inner diameter was 7–15 nm, and the outer diameter was 30–70 nm. Porphyrin tectons, H₄TPPS42- : Sn(IV)TPyP⁴⁺, self-assemble into the nanotubes in a ratio of 2:1, respectively, as determined by the elemental analysis. The photoconductivity of the porphyrin nanotubes was determined to be as high as 3.1 × 10⁻⁴ S m⁻¹, and the dependence of the photoconductance on distance and temperature was investigated. Excitation of the Q-band region with a Q-band of SnTPyP⁴⁺ (550–552 nm) and the band at 714 nm, which is associated with J-aggregation, was responsible for about 34 % of the photoconductive activity of the H₄TPPS42--Sn(IV)TPyP⁴⁺ porphyrin nanotubes. The sensor properties of the H₄TPPS42-- Sn(IV)TPyP⁴⁺ nanotubes in the presence of iodine vapor and salicylate anions down to millimolar range were examined in a chemiresistor sensing mode. We have shown that the porphyrin nanotubes advantageously combine the characteristics of a sensor and a transducer, thus demonstrating their great potential as efficient functional layers for sensing devices and biomimetic nanoarchitectures.

New π-extended catecholato complexes of Pt(ii) and Pd(ii) containing a benzothienobenzothiophene (BTBT) moiety: synthesis, electrochemical behavior and charge transfer properties

Benzothienobenzothiophene (BTBT) and derivatives have received increasing attention as organic field-effect transistor materials and molecular conductors. This report presents the first synthesis of metal complexes involving a BTBT moiety, which was achieved by complexation of 2,2'-bipyridyl complexes of Pt(ii) and Pd(ii) with dihydroxy-substituted BTBT (1) as a new π-extended catecholato ligand (^tBu₂Bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). The resulting complexes M(^tBu₂Bpy)(O₂BTBT) (M = Pt (3Pt) and Pd (3Pd)) were characterized by UV-vis spectroscopy, density functional theory (DFT) calculations, and cyclic voltammetry. The electron donating ability of BTBT was substantially enhanced upon including two oxygen substituents followed by metal coordination. This enabled chemical oxidation of 3Pt and 3Pd with a mild chemical oxidant (ferrocenium hexafluorophosphate) and formation of the one-electron-oxidized state. While 3Pt and 3Pd exhibited an absorption band originating from a catecholate → Bpy ligand-to-ligand charge transfer transition typical of this class of catecholato complexes, the radical cations exhibited a unique π-π* intramolecular charge transfer (ICT) transition absorption in which the π and π* orbitals were the newly incorporated benzothienothiophene-based donor and semiquinonato-based acceptor, respectively. The BTBT⁺ skeleton was electronically divided into two sites by the present chemical modification. The ICT properties of the complexes were found to be modulated by varying the metal ions. These findings offer a new approach to molecular design for (semi)conducting materials using optical properties.

Thermally activated isomeric all-hydrocarbon molecular receptors for fullerene separation

A new all-hydrocarbon macrocycle, cyclo[8](1,3-(4,6-dimethyl)benzene) (CDMB-8) has been reported. As prepared, it exists in Cs symmetry and shows no interaction with fullerenes (e.g., C60 or C70). High temperature (573 K) treatment induces thermal conversion of the material to an isomeric conformer with D4d symmetry as a receptor for fullerene separation.

Tetrathiafulvalene-calix[4]pyrrole: a versatile synthetic receptor for electron-deficient planar and spherical guests

The chemistry of tetrathiafulvalene-calix[4]pyrrole is reviewed with focus on conformational behavior, receptor properties and ionically controlled electron transfer processes.

New dimensions in calix[4]pyrrole: the land of opportunity in supramolecular chemistry

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide. This study is encouraged by the utilization of anions in nature in a plethora of biological systems such as chloride channels and proteins and as polyanions for genetic information. The molecular recognition of anionic species is greatly interesting in terms of their favourable interactions. In this comprehensive review, in addition to giving accounts of some selected syntheses, we illustrated diverse applications ranging from molecular containers to ion transporters and drug carriers of a supramolecular receptor named calix[4]pyrrole. We believe that the present review may act as a catalyst in enhancing the novel applications of calix[4]pyrrole and its congeners in the other dimensions of science and technology.

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide.