Photo‐ and Redox‐Active Dendritic Molecules with Soft,Layered Nanostructures

Molecules with one photoactive group (porphyrin) and multiple redox‐active groups (ferrocenes) are described. The molecules are based on dendritic frameworks, with the ferrocenyl groups attached at the “internal” positions and the porphyrin attached at the focal point, leading to a characteristic layer architecture. Molecules of up to the third generation were synthesized and examined. The results of ¹H NMR spectroscopy and fluorescence quenching indicated that the ferrocenyl groups at the second layer approach the core porphyrin most closely, which is consistent with the results of molecular‐dynamics simulations. The electrochemistry of the molecules was also examined in detail, and a new formula is proposed for the analysis of multiple‐electron transfer in these “redox‐pool” molecules.     

Highly Soluble Porphyrin (TPP)-Perylene Diimide (PDI) Dyad and Triad:Synthesis and Spectroscopic Studies

Novel porphyrin‐perylene diimide dyad (TPP‐PDI) and porphyrin‐perylene diimide‐porphyrin triad (TPP‐PDI‐TPP) were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS, elemental analysis, etc. The variation of fluorescence feature and UV spectra of TPP‐PDI‐TPP triad were investigated at different concentration of CF₃COOH in THF. The incorporation of CF₃COOH leads to the closure of the efficient charge transfer decay. After protonation of porphyrin units, the fluorescence intensity of TPP‐PDI‐TPP triad increased greatly. The fluorescence intensity of TPP‐PDI‐TPP triad restored after addition of triethylamine into the solution. Thus, TPP‐PDI‐TPP triad was a proton‐type fluorescence switch based on acid‐base control. Moreover, different from porphyrin‐perylene type molecular switches reported before, this TPP‐PDI‐TPP triad has wonderful solubility in organic solvents.     

Synthesis,Structure and Photophysical Properties of Ferrocenyl or Mixed Sandwich Cobaltocenyl Ester Linked meso‐Tetratolylporphyrin Dyads

We report here the design and synthesis of porphyrin–metallocene dyads consisting of a metallocene [either ferrocene or mixed sandwich η⁵‐[C₅H₄(COOH)]Co(η⁴‐C₄Ph₄) connected via an ester linkage at meso phenyl position of either free‐base or zinc porphyrin. All these dyad systems were characterized by various spectroscopic and electrochemical methods. A dimeric form of this molecule was observed in the X‐ray crystal structure of Zn‐TTPCo. The absorption spectra of all four dyads indicated the absence of electronic interactions between porphyrin macrocycle and metallocene in the ground state. However, interestingly, in all four dyads, fluorescence emission of the porphyrin was quenched (19–55%) as compared to their monomeric units. The quenching was more pronounced in ferrocene derivatives rather than cobaltocenyl derivatives. The emission quenching can be attributed to the excited‐state intramolecular photoinduced electron transfer from metallocene to singlet excited state of porphyrin and the electron‐transfer rates (k_ET) were established in the range 1.51 × 10⁸ to 1.11 × 10⁹ s^?1. They were found to be solvent dependent.     

Sequential,Ultrafast Energy Transfer and Electron Transfer in a Fused Zinc Phthalocyanine-free-base Porphyrin-C60 Supramolecular Triad

A supramolecular triad composed of a fused zinc phthalocyanine-free-base porphyrin dyad (ZnPc-H₂P) coordinated to phenylimidazole functionalized C₆₀ via metal-ligand axial coordination was assembled, as a photosynthetic antenna-reaction centre mimic. The process of self-assembly resulting into the formation of C₆₀Im:ZnPc-H₂P supramolecular triad was probed by proton NMR, UV-Visible and fluorescence experiments at ambient temperature. The geometry and electronic structures were deduced from DFT calculations performed at the B3LYP/6-31G(dp) level. Electrochemical studies revealed ZnPc to be a better electron donor compared to H₂P, and C₆₀ to be the terminal electron acceptor. Fluorescence studies of the ZnPc-H₂P dyad revealed excitation energy transfer from ¹H₂P* to ZnPc within the fused dyad and was confirmed by femtosecond transient absorption studies. Similar to that reported earlier for the fused ZnPc-ZnP dyad, the energy transfer rate constant, k_ENT was in the order of 10¹² s⁻¹ in the ZnPc-H₂P dyad indicating an efficient process as a consequence of direct fusion of the two π-systems. In the presence of C₆₀Im bound to ZnPc, photoinduced electron transfer leading to H₂P-ZnPc^.+:ImC₆₀^.− charge separated state was observed either by selective excitation of ZnPc or H₂P. The latter excitation involved an energy transfer followed by electron transfer mechanism. Nanosecond transient absorption studies revealed that the lifetime of charge separated state persists for about 120 ns indicating charge stabilization in the triad.     

Synthesis and Spectroscopic Properties of a Covalently Linked Porphyrin–Fullerene C60 Dyad

A covalently linked porphyrin–fullerene C₆₀ dyad 6 was conveniently synthesized by 1,3‐dipolar cycloaddition using 5‐(4‐carbonylphenyl)‐10,15,20‐tris(4‐methoxylphenyl)porphyrin 5, N‐methylglycine and fullerene C₆₀. Spectroscopic studies show that dyad 6 is a promising architecture with potential application as photoactive organic material.     

Formation and Dynamic Behavior of Mono‐ and Bimetallic Cadmium(II) Porphyrin Complexes: Allosteric Control of Coupled Intraligand Metal Migrations

The complexation behavior of a bis‐strapped porphyrin ligand ( 1 ) towards Cd^II has been investigated by ¹H and ¹¹³Cd NMR spectroscopy with the help of X‐ray diffraction structures. The presence of an overhanging carboxylic acid group on each side of the macrocycle is responsible for the instantaneous insertion of the metal ion(s) at room temperature, and allows the formation of bimetallic species with unusual coordination modes at the origin of unique dynamic behaviors. In the absence of base, a C₂‐symmetric bimetallic complex ( 1Cd₂ ) is readily formed, in which the porphyrin acts as a bridging ligand. Both Cd^II ions are bound to the N core and to a COO^? group of a strap. In contrast, the presence of a base induces a two‐step binding process with the successive formation of mono and bimetallic species ( 1^Cd and 1_Cd?CdOAc ). Formally, a Cd^II ion is first inserted into the N core and experiences a strong out‐of‐plane (OOP) displacement due to the binding of an overhanging carbonyl group in an apical position. A second Cd^II ion then binds exclusively to the strap on the opposite side, in a so‐called hanging‐atop (HAT) coordination mode. These two complexes display a fluxional behavior that relies on intraligand migration processes of the metal ion(s). In 1^Cd , the Cd^II ion exchanges between the two equivalent overhanging apical ligands by funneling through the porphyrin ring. In 1_Cd?CdOAc , the two Cd^II ions exchange their coordination mode (HAT?OOP) in a concerted way while staying on their respective side of the macrocycle, in a so‐called Newton’s cradle‐like motion. The intramolecular pathway was notably evidenced by variable temperature ¹¹³Cd heteronuclear NMR experiments. This coupled motion of the Cd^II cations is under allosteric control; the addition of an acetate anion (the allosteric effector) to the “resting” C₂‐symmetric complex 1Cd₂ affords the dissymmetric complex 1_Cd?CdOAc and triggers equilibrium between its two degenerate states. The rate of the swinging motion further depends on the concentration of AcO^?, with a higher concentration leading to a slower motion. As compared with the related Pb^II and Bi^III bimetallic complexes, the Newton’s cradle‐like motion proceeds faster with the smaller Cd^II ion. These results open the way to novel multistable devices and switches.     

Synthesis,Photophysical and Electrochemical Properties of Amide‐Linked Phthalocyanine‐Fullerene Dyad

A new amide‐linked phthalocyanine‐fullerene dyad ZnPc‐C₆₀ was synthesized and characterized. The photophysical and electrochemical properties of the ZnPc‐C₆₀ dyad were investigated. The fluorescence spectrum and quantum yield in different solvents showed the occurrence of photoinduced electron transfer (PET) from the singlet excited ZnPc to C₆₀, which was further confirmed by nanosecond transient absorption spectra and cyclic voltammetry data. The free energy change for charge separation (ΔG_CS) was estimated to be exothermic with ?0.51 eV, which favored the formation of charge‐separation state. The PET from ZnPc to C₆₀ in ZnPc‐C₆₀ made the dyad exhibit stronger reverse saturable absorption performance compared with C₆₀ and the control sample in the Z‐scan experiments, which indicated the synergistic effect of two active moieties in the dyad.     

On the HALA effect in the NMR carbon shielding constants of the compounds containing heavy p‐elements

The heavy atom (HA) effect on the NMR isotropic carbon shielding constants is computationally investigated in the series of model ethanes, ethylenes, and acetylenes, C_βH₃? C_αH₂? XH_n, C_βH₂? C_αH? XH_n, C_βH?C_α? XH_n (n = 0, 1, 2, or 3 depending on X), where X covers p‐elements in the 13–17 groups of the 3–6 periods in as many as 60 compounds. Compounds under study provide diverse bonding situations for the α‐ and β‐carbons, which are characterized by the consecutive increase of the s‐character of the C_β? C_α and C_α? X bonds, being one of the factors influencing spin‐orbit part of the HA on light atom effect (SO‐HALA). The “chalcogen dependence,” “pnictogen dependence,” “tetrel dependence,” and “triel dependence” are established for the 16th, 15th, 14th, and 13th groups, respectively. A well‐known “normal halogen dependence” for the ¹³C NMR chemical shifts, established much earlier for the compounds containing 17th group elements, also revealed itself in all three series under investigation. The dependence of the spin‐orbit effects size depending on the number of the lone electron pairs (LEPs) on HA X has also been investigated. The comparison of theoretical ¹³C NMR chemical shifts with experiment is performed for three representative tellurides. The HALA effect in this series has been shown to be strongly dependent on the number of tellurium LEPs.     

A Five‐layer π‐Aromatic Structure Formed through Self‐assembly of a Porphyrin Trimer and Two Aromatic Guests

In this study we synthesized two‐ and four‐armed porphyrins – bearing two carboxyl and four 2‐aminoquinolino functionalities, respectively, at their meso positions – as a complementary hydrogen bonding pair for the self‐assembly of a D₂‐symmetric porphyrin trimer host. Two units of the two‐armed porphyrin and one unit of the four‐armed porphyrin self‐assembled quantitatively into the D₂‐symmetric porphyrin trimer, stabilized through ammidinium‐carboxylate salt bridge formation, in CH₂Cl₂ and CHCl₃. The porphyrin trimer host gradually bound two units of 1,3,5‐trinitrobenzene between the pair of porphyrin units, forming a five‐layer aromatic structure. At temperatures below ?40 °C, the rates of association and dissociation of the complexes were slow on the NMR spectroscopic time scale, allowing the 1 : 1 and 1 : 2 complexes of the trimer host and trinitrobenzene guest(s) to be detected independently when using less than 2 eq of trinitrobenzene. Vis titration experiments revealed the values of K₁ (2.1±0.4×10⁵ M^?1) and K₂ (2.2±0.06×10⁴ M^?1) in CHCl₃ at room temperature.     

The NMR spectra of porphyrins—12: 13C and proton NMR spectra of the zinc(ii)coproporphyrin isomers2

The ¹³C and proton NMR spectra of the zinc(II) complexes of the tetramethyl esters of the four coproporphyrin type isomers are reported and assigned. Effects of aggregation phenomena on these shifts are discussed and a method involving addition of a slight excess of pyrrolidine is proposed for measurement of the spectra of the “monomeric” species; spectra obtained under these conditions are capable of simple, straight-forward interpretation and assignment in terms of molecular symmetry. Thus, a facile distinction between the type isomers is obtained.The “monomer” chemical shifts so derived allow consistent SCS parameters to be derived. The C_β-Me SCS are shown to be related to the bond order of the C_β-C_β bond in the porphyrin ring, and are thus quite different from the corresponding SCS in pyrroles.Aggregation shifts in the ¹³C and proton spectra are shown to be consistent with the presence of “stacked” aggregates with the ring current of one molecule affecting the other, together with an additional effect on the chemical shifts of the meso carbons, which is probably steric in origin.     

Synthesis and structure analysis of (K[DB18 C6])4(C60)5·12THF containing C60 in three different bonding states

A new fulleride, (K[DB18C6])₄(C₆₀)₅?12 THF, was prepared in solution using the “break‐and‐seal” approach by reacting potassium, fullerene, and dibenzo[18]crown‐6 in tetrahydrofuran. Single crystals were grown from solution by the modified “temperature difference method”. X‐ray analysis was performed revealing a reversible phase transition occurring on cooling. Three different crystal structures of the title compound at different temperatures of data acquisition are addressed in detail: the “high‐temperature phase” at 225 K (C2, Z=2, a=49.055(1), b=15.075(3), c=18.312(4) Å, β=97.89(3)°), the “transitional phase” at 175 K (C2 m, Z=2, a=48.436(5), b=15.128(1), c=18.280(2) Å, β=97.90(1)°), and the “low‐temperature phase” at 125 K (Cc, Z=4, a=56.239(1), b=15.112(3), c=36.425(7) Å, β=121.99(1)°). On cooling, partial radical recombination of C₆₀^.? into the (C₆₀)₂^2? dimeric dianion occurs; this is first time that the fully ordered dimer has been observed. Further cooling leads to formation of a superstructure with doubled cell volume in a different space group. Below 125 K, C₆₀ exists in the structure in three different bonding states: in the form of C₆₀^.? radical ions, (C₆₀)₂^2? dianions, and neutral C₆₀, this being without precedent in the fullerene chemistry, as well. Experimental observations of one conformation exclusively of the fullerene dimer in the crystal structure are further explained on the basis of DFT calculations considering charge distribution patterns. Temperature‐dependent measurements of magnetic susceptibility at different magnetic fields confirm the phase transition occurring at about 220 K as observed crystallographically, and enable for unambiguous charge assignment to the different C₆₀ species in the title fulleride.     

Azafullerene C59N–Phthalocyanine Dyad: Synthesis,Characterisation and Photoinduced Electron Transfer

The synthesis of a new azafullerene C₅₉N–phthalocyanine (Pc) dyad is described. The key step for the synthesis of the C₅₉N–Pc dyad was the formation of the C₅₉N‐based carboxylic acid, which was smoothly condensed with hydroxy‐modified Pc. The structure of the C₅₉N–Pc dyad was verified by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, UV/Vis spectroscopy and MS measurements. The photophysical and electrochemical properties of the C₅₉N–Pc dyad were investigated in both polar and non‐polar solvents by steady state and time‐resolved photoluminescence and absorption spectroscopy, as well as by cyclic voltammetry. Different relaxation pathways for the photoexcited C₅₉N–Pc dyad, as a result of changing the solvent polarity, were found, thus giving rise to energy‐transfer phenomena in non‐polar toluene and charge‐transfer processes in polar benzonitrile. Finally, the detailed quenching mechanisms were evaluated and compared with that of a C₆₀–Pc dyad, which revealed that the different excited‐state energies and reduction potentials of the two fullerene spheres (i.e. C₅₉N vs. C₆₀) strongly diverged in the deactivation pathways of the excited states of the corresponding phthalocyanine dyads.     

Facile Synthesis and Photophysical Properties of Sphere–Square Shape Amphiphiles Based on Porphyrin–[60]Fullerene Conjugates

Molecules constructed from a combination of zero‐dimensional ([60]fullerene (C₆₀)) and two‐dimensional (porphyrin (Por)) nanobuilding blocks represent an intriguing category of sphere–square “shape amphiphiles”. These sphere–square shape amphiphiles possess interesting optoelectronic properties. To efficiently synthesize a large variety of C₆₀–Por shape amphiphiles, a facile route based on Steglich esterification was developed. The synthetic strategy enables the preparation of hydroxy‐functionalized Por precursors ( 9 , 10 , 11 , 12 ) with high purity in a one‐pot procedure. All of the C₆₀–Por shape amphiphiles ( 1 , 2 , 3 , 4 , 5 ) can be readily synthesized in good yields through subsequent Steglich esterification with a highly soluble carboxylic acid derivative of methanofullerene ( 13 ). Photophysical studies indicated weak electronic coupling between the C₆₀ and Por moieties and suggest an edge‐to‐face alignment for the moieties. The fluorescence of electronically excited Por portions of each amphiphile was efficiently quenched, which was indicative of electron transfer from ¹Por to the C₆₀ group(s). Increasing the number of C₆₀ groups on the shape amphiphiles led to more pronounced quenching of the Por fluorescence, which indicated the potential for more effective generation of charge‐separated species, C₆₀^?.Por^+., from the photoexcited C₆₀–Por shape amphiphiles.     

Temperature dependent chemical shift change in 4-substituted[2.2.2.2]paracyclophanes

Temperature dependent NMR spectra of 4-substituted tetrakis[2.2.2.2]paracyclophane (4°-PCP) were measured at low temperature. The high field shift at low temperature was remarkable for the protons meta and para to an electron withdrawing and/or bulky substituent. While the chemical shift change was very small for the aromatic protons of 4°-PCP bearing a not so bulky and electron donating substituent. From these observations it is concluded that the rotation or vibration of a benzene bearing an electron withdrawing and/or bulky substituent around C₂-C₃-C₆-C₉ axis was increasingly frozen as the temperature decreased to a more stable “lateral” (or half “lateral”, the intermediary state between “face” and “lateral”⁴) conformation, in an interesting contrast to the favored face conformation of unsubstituted 4°-PCP at low temperature as well as at room temperature.     

Fullerene–Coumarin Dyad as a Selective Metal Receptor: Synthesis,Photophysical Properties,Electrochemistry and Ion Binding Studies

A coumarin derivative with a malonate unit has been synthesized and used for the preparation of a fullerene–coumarin dyad through the Bingel cyclopropanation method. The newly synthesized dyad is soluble in organic solvents and has been fully characterized with traditional spectroscopic techniques. Electronic interactions between the two components of the dyad were probed with the aid of UV/Vis spectroscopy, fluorescence emission, and electrochemistry measurements. Our studies clearly show the presence of electronic interactions between C₆₀ and modified coumarin in the ground state; efficient electron‐transfer quenching of the singlet excited state of the coumarin moiety by the appended fullerene sphere was also observed. Time‐resolved fluorescence measurements revealed lifetimes for the coumarin–C₆₀ dyad at a maximum of 50 ps, while the quantum yield was reaching unity. Additionally, the redox potentials of the C₆₀–coumarin dyad were determined and the energetics of the electron‐transfer processes were evaluated. Finally, after alkaline treatment of C₆₀–coumarin, which resulted in the deprotection of carboxylate units, the dyad was tested as a metal receptor for divalent metal cations; ion competition studies and fluorescence experiments showed binding selectivity for lead ions.     

An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin‐Crossover Behavior

By employing the subcomponent self‐assembly approach utilizing 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrin or its zinc(II) complex, 1H ‐4‐imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O‐symmetric cages having a confined volume of ca. 1300 ų. The use of iron(II) salts yielded coordination cages in the high‐spin state at room temperature, manifesting spin‐crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X‐ray crystallography, high‐resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state‐of‐the‐art DFT calculations. A remarkably high‐spin‐stabilizing effect through encapsulation of C₇₀ was observed. The spin‐transition temperature T _1/2 is lowered by 20 K in the host–guest complex.     

Synthesis,spectroscopic/electrochemical characterization and DNA interaction study of novel ferrocenyl‐substituted porphyrins

We report the synthesis and characterization of two new meso‐ferrocenylporphyrins, with the ferrocenyl unit attached at the para position of a C₆F₄ group by a C? N bond with ? NH(CH₂)₂NH? ( 2a ) and ? NH(CH₂)₄NH? ( 2b ) spacers. Compounds 2a and 2b were characterized through elemental analyses, electrospray ionization high‐resolution mass spectrometry, ¹H NMR, UV–visible and fluorescence spectroscopies, electrochemistry and spectroelectrochemistry. The free base porphyrin 2 was included for comparison purposes. The binding ability of 2 and the porphyrin derivatives 2a and 2b with calf thymus DNA was determined using UV–visible and fluorescence spectroscopies. The results suggest that the interaction of these systems most probably occurs through π‐stacking by non‐classical modes involving the partial insertion of the C₆F₅ ring between adjacent base pairs on DNA and possible hydrogen interaction with the aliphatic ? NH(CH₂)_nNH? (n = 2 or 4) groups with calf thymus DNA. Moreover, we also demonstrate that porphyrins generate singlet oxygen species and show good photostability after irradiation.     

A Vanadium Porphyrin with Temperature‐Dependent Phase Transformation: Synthesis,Crystal Structures,Supramolecular Motifs and Properties

A vanadium porphyrin, V(O)TMeOPP ( 1 ; TMeOPP=5, 10, 15, 20‐tetrakis(4‐methoxyphenyl)‐21 H, 23H‐porphyrin), has been synthesized by solvothermal reactions and characterized by single‐crystal X‐ray diffractions at room temperature and low temperature to reveal two different structures 1R and 1L , respectively. Both 1R and 1L crystallized in the orthorhombic system, but their space groups were different: Pbca and Pca2₁ for 1R and 1L , respectively. The cell parameters of a, b, and c were different and the cell volume of 1R was larger than that of 1L by circa 200 ų. 1R and 1L were characteristic of an isolated motif with a five‐coordinate vanadium(IV) ion and a saddle‐distorted nonplanar porphyrin macrocycle. Molecules of 1R were interconnected through hydrogen‐bonding interactions to yield a 3D framework; whilst for the low‐temperature phase 1L , there were more hydrogen‐bonding interactions that link the molecules to construct a more‐complex 3D supramolecular network. In a solution of acetone, the title compound exhibited purple and green colors at room temperature and low temperature, respectively, which is unprecedented for vanadium porphyrins. The spectral data of UV/Vis, FT‐IR, and MALDI‐TOF‐MS of 1R and 1L are reported together with the electrochemical data.     

苯醚键相联的C_(60)-卟啉二元化合物的合成、电化学和光谱性质研究(英文)

设计合成了一系列苯醚键相连的C60-卟啉二元化合物及其金属锌配合物:H2Por-p-C60、H2Por-m-C60、H2Por-o-C60、ZnPor-p-C60、ZnPor-m-C60和ZnPor-o-C60,通过质谱、元素分析和核磁共振氢谱对它们的结构进行了表征。基态的电子吸收光谱和电化学研究表明在这些二元体系中C60和卟啉之间存在明显的相互作用。荧光光谱研究表明卟啉单元的荧光几乎被C60单元完全淬灭,并且它们之间的连接位置对荧光淬灭的效率具有显著影响。     

Self‐Assembly of a Highly Organized,Hexameric Supramolecular Architecture: Formation,Structure and Properties

Two derivatives, ³ L and ⁹ L , of a ditopic, multiply hydrogen‐bonding molecule, known for more than a decade, have been found, in the solid state as well as in solvents of low polarity at room temperature, to exist not as monomers, but to undergo a remarkable self‐assembly into a complex supramolecular species. The solid‐state molecular structure of ³ L , determined by single‐crystal X‐ray crystallography, revealed that it forms a highly organized hexameric entity ³ L ₆ with a capsular shape, resulting from the interlocking of two sets of three monomolecular components, linked through hydrogen‐bonding interactions. The complicated ¹H NMR spectra observed in o‐dichlorobenzene (o‐DCB) for ³ L and ⁹ L are consistent with the presence of a hexamer of D₃ symmetry in both cases. DOSY measurements confirm the hexameric constitution in solution. In contrast, in a hydrogen‐bond‐disrupting solvent, such as DMSO, the ¹H NMR spectra are very simple and consistent with the presence of isolated monomers only. Extensive temperature‐dependent ¹H NMR studies in o‐DCB showed that the L ₆ species dissociated progressively into the monomeric unit on increasing th temperature, up to complete dissociation at about 90 °C. The coexistence of the hexamer and the monomer indicated that exchange was slow on the NMR timescale. Remarkably, no species other than hexamer and monomer were detected in the equilibrating mixtures. The relative amounts of each entity showed a reversible sigmoidal variation with temperature, indicating that the assembly proceeded with positive cooperativity. A full thermodynamic analysis has been applied to the data.