Rare Guest-Induced Electrical Conductivity of Zn-Porphyrin Metallacage Inclusion Complexes Featuring π-Donor/Acceptor/Donor Stacks.

Charge-transfer (CT) interactions between co-facially aligned π-donor/acceptor (π-D/A) arrays engender unique optical and electronic properties that could benefit (supra)molecular electronics and energy technologies. Herein, we demonstrate that a tetragonal prismatic metal-organic cage (MOC18+) having two parallel π-donor tetrakis(4-carboxyphenyl)-Zn-porphyrin (ZnTCPP) faces selectively intercalate planar π-acceptor guests, such as hexaazatriphenylene hexacarbonitrile (HATHCN), hexacyanotriphenylene (HCTP), and napthanelediimide (NDI) derivatives, forming 1:1 πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads. The π-acidity of intercalated π-acceptors (HATHCN ≫ HCTP ≈ NDIs) dictated the nature and strength of their interactions with the ZnTCPP faces, which in turn influenced the binding affinities (Ka) and optical and electronic properties of corresponding πA@MOC18+ inclusion complexes. Owing to its strongest CT interaction with ZnTCPP faces, the most π-acidic HATHCN guest enjoyed the largest Ka (5 × 106 M-1), competitively displaced weaker π-acceptors from the MOC18+ cavity, and generated the highest electrical conductivity (2.1 × 10-6 S/m) among the πA@MOC18+ inclusion complexes. This work demonstrates a unique through-space charge transport capability of πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads, which generated tunable electrical conductivity, which is a rare but much coveted electronic property of such supramolecular assemblies that could further expand their utility in future technologies.

Pt(ii)-coordinated tricomponent self-assemblies of tetrapyridyl porphyrin and dicarboxylate ligands: are they 3D prisms or 2D bow-ties?

Thermodynamically favored simultaneous coordination of Pt(ii) corners with aza- and carboxylate ligands yields tricomponent coordination complexes with sophisticated structures and functions, which require careful structural characterization to paint accurate depiction of their structure-function relationships. Previous reports claimed that heteroleptic coordination of cis-(Et3P)2PtII with tetrapyridyl porphyrins (M'TPP, M' = Zn or H2) and dicarboxylate ligands (XDC) yielded 3D tetragonal prisms containing two horizontal M'TPP faces and four vertical XDC pillars connected by eight Pt(ii) corners, even though such structures were not supported by their 1H NMR data. Through extensive X-ray crystallographic and NMR studies, herein, we demonstrate that self-assembly of cis-(Et3P)2PtII, M'TPP, and four different XDC linkers having varied lengths and rigidities actually yields bow-tie (⋈)-shaped 2D [{cis-(Et3P)2Pt}4(M'TPP) (XDC)2]4+ complexes featuring a M'TPP core and two parallel XDC linkers connected by four heteroleptic PtII corners instead of 3D prisms. This happened because (i) irrespective of their length (∼7-11 Å) and rigidity, the XDC linkers intramolecularly bridged two adjacent pyridyl-N atoms of a M'TPP core via PtII corners instead of connecting two cofacial M'TPP ligands and (ii) bow-tie complexes are entropically favored over prisms. The electron-rich ZnTPP core of a representative bow-tie complex selectively formed a charge-transfer complex with highly π-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-heaxacarbonitrile but not with a π-donor such as pyrene. Thus, this work not only produced novel M'TPP-based bow-tie complexes and demonstrated their selective π-acid recognition capability, but also underscored the importance of proper structural characterization of supramolecular assemblies to ensure accurate depiction of their structure-property relationships.

A New Electrically Conducting Metal-Organic Framework Featuring U-Shaped cis-Dipyridyl Tetrathiafulvalene Ligands.

A new electrically conducting 3D metal-organic framework (MOF) with a unique architecture was synthesized using 1,2,4,5-tetrakis-(4-carboxyphenyl)benzene (TCPB) a redox-active cis-dipyridyl-tetrathiafulvalene (Z-DPTTF) ligand. While TCPB formed Zn2(COO)4 secondary building units (SBUs), instead of connecting the Zn2-paddlewheel SBUs located in different planes and forming a traditional pillared paddlewheel MOF, the U-shaped Z-DPTTF ligands bridged the neighboring SBUs formed by the same TCPB ligand like a sine-curve along the b axis that created a new sine-MOF architecture. The pristine sine-MOF displayed an intrinsic electrical conductivity of 1 × 10-8 S/m, which surged to 5 × 10-7 S/m after I2 doping due to partial oxidation of electron rich Z-DPTTF ligands that raised the charge-carrier concentration inside the framework. However, the conductivities of the pristine and I2-treated sine-MOFs were modest possibly because of large spatial distances between the ligands that prevented π-donor/acceptor charge-transfer interactions needed for effective through-space charge movement in 3D MOFs that lack through coordination-bond charge transport pathways.

The Advent of Electrically Conducting Double-Helical Metal-Organic Frameworks Featuring Butterfly-Shaped Electron-Rich π-Extended Tetrathiafulvalene Ligands.

To diversify metal-organic framework (MOF) structures beyond traditional Euclidean geometries and to create new charge-delocalization pathways beneficial for electrical conductivity, we constructed a novel double-helical MOF (dhMOF) by introducing a new butterfly-shaped electron-rich π-extended tetrathiafulvalene ligand equipped with four benzoate groups (ExTTFTB). The face-to-face oriented convex ExTTFTB ligands connected by Zn2(COO)4 paddlewheel nodes formed ovoid cavities suitable for guest encapsulation, while π-π-interaction between the ExTTFTB ligands of neighboring strands helped create new charge-delocalization pathways in iodine-mediated partially oxidized dhMOF. Iodine vapor diffusion led to oxidation of half of the ExTTFTB ligands in each double-helical strand to ExTTFTB•+ radical cations, which putatively formed intermolecular ExTTFTB/ExTTFTB•+ π-donor/acceptor charge-transfer chains with the neutral ExTTFTB ligands of an adjacent strand, creating supramolecular wire-like charge-delocalization pathways along the helix seams. In consequence, the electrical conductivity of dhMOF surged from 10-8 S/m up to 10-4 S/m range after iodine treatment. Thus, the introduction of the electron-rich ExTTFTB ligand with a distinctly convex π-surface not only afforded a novel double-helical MOF architecture featuring ovoid cavities and unique charge-delocalization pathways but also, more importantly, delivered a new tool and design strategy for future development of electrically conducting stimuli-responsive MOFs.

Efficient MOF-Sensitized Solar Cells Featuring Solvothermally Grown [100]-Oriented Pillared Porphyrin Framework-11 Films on ZnO/FTO Surfaces.

Owing to their abilities to assemble and organize a large number of redox and photoactive components in highly ordered periodic fashion, crystalline porous metal-organic frameworks (MOFs) have the potential to execute myriad complex functions, including charge transport and light to electrical energy conversion when the required conditions are fulfilled. Herein, we demonstrate an unprecedented spontaneous solvothermal growth of precisely [100]-oriented pillared porphyrin framework-11 (PPF-11) films featuring vertically aligned Zn-tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) walls and horizontally aligned 2,2'-dimethyl-4,4'-bipyridine beams attached to annealed ZnO-fluorine-doped tin oxide (FTO) surfaces and their remarkable photovoltaic performance in liquid-junction solar cells. The [100]-oriented PPF-11/ZnO-FTO photoanodes displayed excellent photovoltaic response (short-circuit current ( JSC): 4.65 mA/cm2, open-circuit voltage ( VOC): 470 mV, power conversion efficiency: 0.86%) that easily outperformed all control devices as well as previously reported porphyrin and Ru(bpy)32+-based visible light-harvesting MOFs with 10-1000 times greater photocurrent density and 2-375 times higher efficiency. The superior photovoltaic behavior of [100]-oriented PPF-11/ZnO films compared to epitaxially grown MOF thin films on insulating self-assembled monolayers and drop-cast PPF films with different orientations can be attributed to several factors, including better charge separation, transport, and injection capabilities of the former. The noncatenated PPF-11 was able to host electron-deficient C60 guests, filling in nearly half of its cavities and engage them in ZnTCPP/C60 charge-transfer interaction. However, the C60-doped PPF-11/ZnO films displayed much weaker photovoltaic response than undoped [100]-oriented PPF-11/ZnO films presumably due to exclusion of I-/I3- electrolyte from the C60-occupied cavities and the inability of isolated C60 guests to support long-range charge movement.

Lowering Band Gap of an Electroactive Metal-Organic Framework via Complementary Guest Intercalation.

A new honeycomb-shaped electroactive metal-organic framework (MOF) has been constructed from an electron deficient naphthalenediimide (NDI) ligand equipped with two terminal salicylic acid groups. π-Intercalation of electron-rich planar tetrathiafulvalene (TTF) guests between the NDI ligands stacked along the walls lowers the electronic band gap of the material by ca. 1 eV. An improved electron delocalization through the guest-mediated π-donor/acceptor stacks is attributed to the diminished band gap of the doped material, which forecasts an improved electrical conductivity.

Photochemical and Electrochemical Triggered Bis(hydrazone) Switch.

Herein, we report the synthesis of a double hydrazone capable of undergoing photochemical E/Z isomerization through the imine double bonds. The bis(hydrazone) 1-E,E can be considered as a "two-arm" system in which the controlled movement of each arm is obtained by photo-modulation, making possible the appearance of two isolable metastable isomeric states 1-E,Z and 1-Z,Z. Such states are characterized by very specific structural, optical, and electrochemical properties. The latter allows the reversible return from either 1-E,Z or 1-Z,Z to the 1-E,E state. Our results are of great importance in the further development of molecular machines and photochemically controlled reactions by introducing for the first time double hydrazones as tunable photochemical switches.

A DFT study on Dichloro {(E)-4-dimethylamino-N'-[(pyridin-2-yl) methylideneK N] benzohydrazide-k0}M2+ (M = Zn, Cu, Ni, Fe, Mn, Ca and Co) complexes: Effect of the metal over association energy and complex geometry / Un estudio DFT en complejos Dicloro {(E)-4-dimetilamino-N'-[(piridin-2-il) metilideno-K N] benzohidrazida-K0} M2+ (M = Zn, Cu, Ni, Fe, Mn, Ca y Co): efecto del metal sobre la energía de asociación y la geometría del complejo / Um estudo DFT nos complexos Dicloro {(E)-4-dimetilamino-N'-[(piridin-2-il) metilideno -K N] benzohidrazida-K0} M2+ (M = Zn, Cu, Ni, Fe, Mn, Ca y Co): efeito do metal sobre a energia de associação e a geometria do complexo

The molecular geometry of (E)-4-dimethylamino-N'-[(pyridin-2yl)methylidene-kN]benzohydrazide (C15H16N4O) complexed with M²+ (M=Zn, Cu, Ni, Fe, Mn, Ca and Co) ions was calculated, using density functional theory (B3LYP) with 6-31G(d, p) basis set. Vibrational frequencies were computed in order to verify the absence of imaginary vibrational frequencies, fact that confirms the global minimum in geometry optimization. Molecular geometry parameters (bond lengths and angles) for Cu²+ and Zn²+ complexes were compared with crystallographic data previously reported, showing good correlation. Binding energies for all complexes were computed at the B3LYP/6-31G++(d, p) level of theory. These calculations indicate that Cu-L is the lowest favorable complex, Cu²+ corresponds to the smallest cation on the present study. On the other hand, Ca-L, one of the less favorable complex, corresponds to the largest cation analyzed in the present study. Molecular orbital analysis was carried out showing variations in ΔE HOMO-LUMO values as a function of the metallic ion employed.

La geometría molecular de la (E)-4-dimetilamino-N'-[(piridin-2-il) metilideno-kN] benzohidrazida (C15H16N4O) acomplejada con iones M²+ (M=Zn, Cu, Ni, Fe, Mn, Ca y Co) se calculó usando la teoría funcional de densidad (B3LYP) empleando un conjunto de bases 6-31G(d, p). Las frecuencias vibracionales fueron calculadas con el propósito de comprobar la ausencia de frecuencias vibracionales imaginarias, hecho que confirma el mínimo global en la optimización de la geometría. Los parámetros de la geometría molecular (longitudes de enlace y ángulos) para los complejos de Cu²+ y Zn²+ fueron comparados con datos cristalográficos previamente reportados, mostrando una buena correlación. Las energías de asociación para todos los complejos fueron determinadas a un nivel de teoría B3LYP/6-31G++(d, p) mostrando que el complejo menos favorable es Cu-L, correspondiente al catión más pequeño del estudio. Por otro lado Ca-L, uno de los menos estables, corresponde al catión más grande analizado. Se llevó a cabo un análisis de orbitales moleculares en el cual los complejos exhibieron diferentes valores de ΔE HOMO-LUMO en función del metal empleado.

A geometria molecular da (E)-4-dimetilamino-N'-[(piridin-2-il) metilideno-kN] benzohidrazida (C15H16N4O) acomplexada com íons M²+ (M=Zn, Cu, Ni, Fe, Mn, Ca y Co) foi calculada usando a teoria funcional da densidade (B3LYP) utilizando um conjunto de bases 6-31G(d, p). As frequências vibracionais foram calculadas com o objetivo de comprovar a ausência de frequências vibracionais imaginárias, fato que confirma o mínimo global na otimização da geometria. Os parâmetros da geometria molecular (longitudes de enlace e ângulos) para os complexos de Cu²+ y Zn²+ foram comparados com dados cristalográficos previamente reportados e mostraram boa correlação. As energias de associação para todos os complexos foram determinadas ao nível de teoria B3LYP/6-31G++(d, p) mostrando que o complexo menos favorável é Cu-L, correspondente ao cátion mais pequeno do estudo. Por outro lado Ca-L, um dos menos estáveis, corresponde ao cátion mais grande analisado. Foi feita uma análise de orbitais moleculares no qual os complexos exibiram diferentes valores de ΔE HOMO-LUMO em função do metal utilizado.

Acylhydrazone-based dynamic combinatorial libraries: study of the thermodynamic/kinetic evolution, configurational and coordination dynamics / Librerías combinatorias dinámicas basadas en acil-hidrazona: estudio del desarrollo termodinámico/cinético, dinámicas de configuración y de coordinación / Livrarias combinatórias dinâmicas baseadas na acil-hidrazona: estudo da evolução cinética/termodinâmica, dinâmicas de configuração e da coordenação

The kinetic and thermodynamic selectivity of acylhydrazone formation in dynamic combinatorial libraries (DCL) is described. Competition reactions were generated from hydrazides: isoniazid, 4-nitro-benzohydrazide, 4-dimethylamino-benzohydrazide, and nicotinic hydrazide as well as the aldehyde derivatives: benzaldehyde and 2-pyridine-carboxaldehyde. The obtained species and the distribution of the DCLs were monitored by 'H-NMR spectroscopy finding that those acylhydrazones containing the 4-dimethylamino-benzohydrazide moiety are both the kinetic and thermodynamic product of their respective libraries. Configurational and coordination dynamics for some of these libraries were also investigated. The obtained results allowed the study of the redistribution of components and the amplification of one or more products using light and metal ions as physical and chemical templates, respectively.

Se describe la selectividad cinética y termodinámica de la formación de acil-hidrazona en bibliotecas combinatorias dinámicas (DCL). Se generaron reacciones competitivas a partir de hidrazidas: isoniazida, 4-nitro-benzohidrazida, 4-dimetilamino-benzohidrazida y hidrazida nicotínica; así como a partir de los derivados de aldehído: benzaldehído y 2-piridin-carboxaldehido. Las especies obtenidas y la distribución de los DCLs fueron monitoreados mediante espectroscopia 'H-NMR, encontrándose que las acil-hidrazonas que contenían la 4-dimetilamino-benzohidrazida son tanto el producto cinético, como el termodinámico de sus respectivas bibliotecas. También se investigaron las dinámicas de configuración y de coordinación para algunas de estas bibliotecas. Los resultados obtenidos permitieron estudiar la redistribución de los componentes y la amplificación de uno o más productos usando luz e iones metálicos como plantillas físicas y químicas, respectivamente.

É descrita a seletividade cinética e termodinâmica da formação de acil-hidrazonas em livrarias combinatórias dinâmicas (DLC). Foram geradas reações competitivas a partir das hidrazidas: isoniazida, 4-nitro-benzohidrazida, 4-dimetilamino-benzohidrazida e hidrazida nicotínica; além dos derivados de aldeído: benzaldeído e 2-piridin-carboxaldeído. As espécies obtidas e a distribuição dos DLCs foram monitorados mediante espectroscopia 'H-NMR, foi encontrado que as acil-hidrazonas que continham à 4-dimetilamino-benzohidrazida são tanto o produto cinético como o termodinâmico de suas respectivas livrarias. Também investigaram-se as dinâmicas de configuração e coordenação para algumas destas livrarias. Os resultados obtidos permitem estudar a redistribuicao dos componentes e a amplificação de um ou mais produtos usando luz e íons metálicos como modelos físicos e químicos, respectivamente.