Metalla-Carbaporphyrinoids Consisting of an Acyclic N-Confused Tetrapyrrole Analogue Served as Stable Near-Infrared-II Dyes.

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique dπ-pπ-conjugated electronic structures involving the metal dπ-ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF2 and 1Pt-BF2) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ-pπ-conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes.

Reversible open-closed conformational switching of nano-size metalloporphyrin dimers triggered by light and temperature.

The current work demonstrates the reversible control of substantial molecular motion in 'nano-sized' molecules, where two structural isomers can 'open' and 'close' their cavities in response to light or heat. The isomers differ widely in their photophysical properties, including colour, polarity, two-photon absorption and π-conjugation, and can easily be separated through column chromatography and thus have wide applicability.

Synthesis and photothermal conversion properties of sandwich N-fused porphyrin rhodium-µ-dichloride dimer complexes: π-extended analog of pentamethylcyclopentadienyl dirhodium(III)-µ-dichloride dimer.

Anionic cyclopentadienyl (Cp) and its pentamethyl-substituted derivative (Cp*) serve as crucial ligands for creating stable π-coordinated materials, including catalysts. From a structural perspective, the π-extended analog of Cp, known as an N-fused porphyrin (NFP), is recognized as an intriguing 18π aromatic chromophore, offering near-infrared (NIR) optical properties that can be fine-tuned through metal complexation. When coordinated with rhodium at the central NFP core, it forms a sandwich binuclear rhodium(III) complex along with terminal and bridging chloride ligands, denoted as Rh-1, and its bromo derivative, Rh-1-Br. In contrast to the bis-NFP complex of iron(II) reported previously by our team, both Rh-1 and Rh-1-Br complexes exhibit strong NIR optical properties and narrow HOMO-LUMO energy gaps, attributed to minimal orbital interactions between the two co-facial NFP ligands. Leveraging these NIR absorption properties, we assessed the photothermal conversion properties of Rh-1 and ligand 1, revealing high conversion efficiency. This suggests their potential application as photothermal agents for use in photothermal therapy.

Stable Dication Diradicals of Triply Fused Metallo Chlorin-Porphyrin Heterodimers: Impact of the Bridge on the Control of Spin Coupling to Reactivity.

We report an unexpected rearrangement, controlled by the nature of the bridge, leading to the formation of novel, remarkably stable triply fused dinickel(II)/dicopper(II) chlorin-porphyrin dication diradical heterodimers in excellent yields. Here, a dipyrromethene bridge gets completely fused between two porphyrin macrocycles with two new C-C and one C-N bonds. The two macrocycles exhibit extensive π-conjugation through the bridge, which results in an antiferromagnetic coupling between the two π-cation radicals. In addition, the macrocyclic distortion also favours a rare intramolecular ferromagnetic interaction between the CuII and π-cation radical spins to form a triplet state. The structural and electronic perturbation in the unconjugated dication diradical possibly enables the bridging pyrrolic nitrogen to undergo a nucleophilic attack at the nearby ß-carbon of the porphyrin π-cation radical with a computed free energy barrier of >20 kcal mol-1 which was supplied in the form of reflux condition to initiate such a rearrangement process. UV-vis, EPR and ESI-MS spectroscopies were used to monitor the rearrangement process in situ in order to identify the key reactive intermediates leading to such an unusual transformation.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity.

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C60)n or (2•C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 104 M-1 and (4.3 ± 0.9) × 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑µ), increases upon fullerene inclusion (e.g., ϕ∑µ = 1.53 × 10-4 cm2 V-1 s-1 for C60⊂(1a)2 and ϕ∑µ = 1.45 × 10-4 cm2 V-1 s-1 for C70⊂(1a)2 vs ϕ∑µ = 2.49 × 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

Antiaromatic Sapphyrin Isomer: Transformation into Contracted Porphyrinoids with Variable Aromaticity.

Sapphyrin is a pentapyrrolic expanded porphyrin with a 22π aromatic character. Herein, we report the synthesis of a 20π antiaromatic sapphyrin isomer 1 by oxidative cyclization of a pentapyrrane precursor P5 with a terminal ß-linked pyrrole. The resulting isomer 1, containing a mis-linked bipyrrole unit in the skeleton, exhibits a reactivity for further oxidation due to the distinct antiaromatic electronic structure, affording a fused macrocycle 2, possessing a spiro-carbon-containing [5.6.5.6]-tetracyclic structure. Subsequent treatment with an acid afforded a weakly aromatic pyrrolone-appended N-confused corrole 3, and thermal fusion gave a [5.6.5.7]-tetracyclic-ring-embedded 14π aromatic triphyrin(2.1.1) analog 4. The cyclization at the mis-linked pyrrole moiety of P5 played a crucial role in synthesizing the antiaromatic porphyrinoid susceptible to facile transformation to novel porphyrinoids with variable aromaticity.

Exercise training using hybrid assistive limb (HAL) lumbar type for locomotive syndrome: a pilot study.

BACKGROUND: With a rapidly aging population in Japan, locomotive syndrome is becoming an increasingly serious social problem. Exercise therapy using the lumbar type HAL, which is a wearable robot suit that can assist voluntary hip joint motion, would be expected to cause some beneficial effects for people with locomotive syndrome. The purpose of this study was to assess whether the deterioration of low back pain and any other adverse events would occur following HAL exercise therapy. Moreover, the changes of motor ability variables were evaluated. METHODS: We enrolled 33 participants (16 men, 17 women) with locomotive syndrome in this study. They received exercise training (sit-to-stand, lumbar flexion-extension, and gait training) with HAL (in total 12 sessions). We assessed the change of low back pain (lumbar VAS). More than 50% and 25 mm increase compared to baseline was defined as adverse events. One-leg standing time (OLST), 10-m walking test (10MWT), Timed Up and Go test (TUG), 1-min sit-to-stand test (1MSTS), FIM mobility scores and EQ-5D were measured. RESULTS: Of the 33 participants, 32 (16 men, 16 women) (97.0%) completed all 12 exercise training sessions using the lumbar type HAL. One woman aged 82 years withdrew because of right upper limb pain after the second session regardless of the use of HAL. There was no participant who had deterioration of low back pain. Any other adverse events including external injuries and/or falling, skin disorders, uncontrollable cardiovascular or respiratory disorders, and other health disorders directly related to this exercise therapy did not occur. Several outcome measures of motion ability including OLST, TUG and 1MSTS, EQ VAS and lumbar pain improved significantly after this HAL training. CONCLUSIONS: Almost all patients with locomotive syndrome completed this exercise training protocol without any adverse events related to HAL. Furthermore, balance function variables including OLST, TUG and 1MSTS improved after this HAL exercise therapy even though mobility function variables including 10MWT and FIM mobility scores did not show any significant change. These findings suggest that the exercise therapy using the lumbar type HAL would be one of the options for the intervention in locomotive syndrome.

Solvent-Controlled Self-Assembled Oligopyrrolic Receptor.

We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure (10)2 in a less polar, non-coordinating solvent (e.g., CHCl3). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N,N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) "zig-zag" polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H2SO4, HNO3, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host-guest complex by simple aqueous washing. It was observed that relatively stronger acids with pKa < -1.92 in water were able to interact with the receptor, as inferred from 1H NMR titration in tetrahydrofuran-d8 (THF-d8) and ultraviolet-visible (UV-vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.

Iridium Complex of N-Fused Bilatrienone: Oxidative Cleavage of N-Fused Porphyrin Induced by Iridium-Cyclooctadiene Complexation.

N-fused porphyrin (NFP) is a unique class of photostable near-infrared dyes with an 18π aromatic tetrapyrrole macrocyclic skeleton containing a tri-fused pentacyclic moiety. Here, the synthesis of an iridium complex of N-fused bilatrienone is reported as the degradation product of Ir-cyclooctadiene (cod)-induced oxidative cleavage of NFP under aerobic conditions. Similar to the native bilin chromophores, the ring-opened complex featured a broken π-conjugation circuit and exhibited a broad visible absorption band. In contrast, metalation of NFP using an iridium(I)(cod) complex under an inert atmosphere resulted in the formation of a cod-isomerized (κ1 ,η3 -C8 H12 )-Ir complex.

Chiral Interlocked Corrole Dimers Directly Linked at Inner Carbon Atoms of Confused Pyrrole Rings.

A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C-C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials.

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.

Ruthenium(iv) N-confused porphyrin µ-oxo-bridged dimers: acid-responsive molecular rotors.

Ruthenium(iv) N-confused porphyrin µ-oxo-bridged complexes were synthesized via oxidative dimerization of a ruthenium(ii) N-confused porphyrin complex using 2,2,6,6-tetramethylpiperidine 1-oxyl. The deformed core planes in the dimers conferred a relatively high ring rotational barrier of ca. 16 kcal mol-1. Rotation of the complexes was controlled by protonating the peripheral nitrogen.

Expanded N-Confused Phlorin: A Platform for a Multiply Fused Polycyclic Ring System via Oxidation within the Macrocycle.

Novel interrupted π-conjugated macrocycles derived from expanded porphyrinoids were synthesized, and their unique reactivity was investigated in this work. The specific porphyrin analogs, so-called phlorins and isoporphyrins, possess a meso-sp3 methylene moiety, showing inner 3NH and 1NH pyrrolic cores, respectively, and extended near-infrared (NIR) absorption. Expanded N-confused pentapyrrolic phlorin analog 1 bears an interrupted cyclic π-conjugated system that is featured by a distinct higher HOMO and a lower LUMO. Oxidation of 1 allowed structural transformations through the expanded isoporphyrin-like species 2. One of the representative products is a spiro-carbon-bridged multiply N-fused product 3 comprising a fused [5.6.5.7.6.5]-hexacyclic ring obtained by oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone. When magic blue was used as the oxidant, an aromatic N-confused pentaphyrin 4 was obtained via migration of one of the meso-phenyl groups to the ß-position of the neighboring pyrrolic ring. By employing the flexible cavity of 1 for metal coordination, Pd(II) complexation occurred with a specific meso oxygenation to give a bimetallic complex 5. In contrast to the rich oxidation reactions, reduction of 1 with NaBH4 resulted in the regioselective nucleophilic hydrogen substitution reaction at the para position of one of the meso-C6F5 groups. These results provide a practical approach for synthesizing novel interrupted or aromatic π-conjugated frameworks showing NIR absorptions.

Synthesis of Helically π-Extended N-Confused Porphyrin Dimer via meso-Bipyrrole-Bridge with Near-Infrared-II Absorption Capability.

Quinoidal dimeric porphyrin dye synthesis exhibiting second near-infrared (NIR-II) absorbability is described herein. A precisely designed meso-pyrrolyl-substituted N-confused porphyrin possesses a distinct metal coordination site at the periphery. Nickel metalation of this compound led to the oxidative C-H coupling between adjacent α-pyrrole rings, affording two dimeric complexes, which exhibited intense NIR-II absorptions ranging from 1000 to 1400 nm. As was evidenced by decreased aromaticity, the quinoidal resonant structures contributed to the emergence of photoacoustic spectral capabilities in the NIR-II window. Thus, the potential of these compounds as prototypical contrast agents in various bioimaging applications has been demonstrated.

Fundamental Study on Arsenic(III) Halides (AsX3; X = Br, I) toward the Construction of C3-Symmetrical Monodentate Arsenic Ligands.

Arsenic ligands have attracted considerable attention in coordination chemistry. Arsenic(III) halides are the most important starting materials in the preparation of monodentate arsenic ligands. In this work, we optimized the synthetic methodologies of arsenic(III) halides (AsX3; X = Br, I) and examined the difference of their physical properties such as solubility to organic solvent and reactivity to nucleophiles. In addition, a wide variety of monodentate arsenic ligands were prepared with the obtained AsX3. Finally, the obtained monodentate arsenic ligands were utilized for copper-free Sonogashira cross-coupling reaction in the reaction system with porphyrin. The results showed that monodentate arsenic ligands have higher catalytic activity compared with triphenylphosphine because of the difference of the electronic features of lone pairs between arsenic and phosphorus atoms.

NH Tautomerism of N-Confused Porphyrin: Solvent/Substituent Effects and Isomerization Mechanism.

The effects of substituents and solvents on the NH tautomerism of N-confused porphyrin (2) were investigated. The structures, electronic states, and aromaticity of NH tautomers (2-2H and 2-3H) were studied by absorption and nuclear magnetic resonance (1H, 13C, and 15N) spectroscopies, single-crystal X-ray diffraction analysis, and theoretical calculations. The relative stability of the tautomers is highly affected by solvents, with the 3H-type tautomer being more stable in nonpolar solvents, while the 2H-type tautomer being highly stabilized in polar solvents with high donor numbers such as N,N-dimethylformamide (DMF), pyridine, and acetone. Electron-withdrawing groups on the meso-aryl substituents as well as the methyl group at the ortho position also stabilize the 2H-type tautomer. Kinetically, the tautomerism rate is significantly influenced by solvent and concentration, and a particularly large activation entropy (ΔS⧧) is obtained in pyridine. The first-order deuterium isotope effect on the reaction rates of NH tautomerism (kH/kD) is determined to be 2.4 at 298 K. On the basis of kinetic data, the mechanism of isomerization is identified as an intramolecular process, including the rotation of the confused pyrrole in pyridine/chloroform and DMF/chloroform mixed solvent systems, and as a pyridine-mediated process in pyridine alone.

Near-Infrared-III-Absorbing and -Emitting Dyes: Energy-Gap Engineering of Expanded Porphyrinoids via Metallation.

The synthesis of organometallic complexes of modified 26π-conjugated hexaphyrins with absorption and emission capabilities in the third near-infrared region (NIR-III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis-PdII and bis-PtII complexes of hexaphyrin via N-confusion modification led to substantial metal dπ -pπ interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO-LUMO energy gap. A remarkable long-wavelength shift of the lowest S0 →S1 absorption beyond 1700 nm was achieved with the bis-PtII complex, t-Pt2 -3. The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t-Pt2 -3 potentially useful as a NIR-III PA contrast agent. The rigid bis-PdII complexes, t-Pd2 -3 and c-Pd2 -3, are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR-III-emissive and photoacoustic-response capabilities.

Copper 1,19-Diaza-21,24-dicarbacorrole: A Corrole Analogue with an N-N Linkage Stabilizes a Ground-State Singlet Organocopper Species.

A copper complex of a heterocorrole analogue with an N-N linkage, 1,19-diaza-21,24-dicarbadibenzocorrole (Cu-5), was successfully synthesized via oxidative metalation-cyclization of a tetrapyrrolic precursor. The N-N linkage in the skeleton of Cu-5, which serves as a mediator of π-electron delocalization, features an 18π aromatic system. The electronic structure of Cu-5 is best described as a ground-state singlet species stabilized by the distinct NNCC coordination core. This finding shows how the ligand's design can be used to modulate the Cu 3 d x 2 - y 2 orbital energy, thereby making such compounds invaluable for copper-based catalytic applications.

Synthesis, Photophysical Properties and Computational Studies of beta-Substituted Porphyrin Dyads.

Beta-pyrrole-substituted porphyrin dyads connected by ethynyl linkage to N-butylcarbazole or triphenylamine donors are reported. Donor-π-acceptor type beta-substituted porphyrin dyads and their Zn(II) and Pd(II) complexes were characterized by MALDI-MS, NMR, UV-vis absorption, fluorescence and cyclic voltammetry techniques. The S1 emission dynamics were analyzed by time-resolved spectroscopy (TCSPC); dyads exhibited efficient energy transfer up to 93% from beta-donors (N-butylcarbazole or triphenylamine group) to the porphyrin core. The efficiency of energy transfer for the beta-substituted porphyrin dyads were much higher than those of the corresponding meso-substituted porphyrin dyads, reflecting enhanced communications between the beta-donors and the porphyrin core. The Pd(II) dyads, showed characteristic phosphorescence in the near IR region and very efficient singlet oxygen quantum yields (53-60%); these dyads are promising candidates for photocatalytic oxidations of organic compounds. The donor-acceptor interaction between the porphyrin core and the beta-donors was supported by the DFT studies in the porphyrin dyads.

Semiconducting Supramolecular Organic Frameworks Assembled from a Near-Infrared Fluorescent Macrocyclic Probe and Fullerenes.

We report here a new extended tetrathiafulvalene (exTTF)-porphyrin scaffold, 2, that acts as a ball-and-socket receptor for C60 and C70. Supramolecular interactions between 2 and these fullerenes serve to stabilize 3D supramolecular organic frameworks (SOFs) in the solid state formally comprising peapod-like linear assemblies. The SOFs prepared via self-assembly in this way act as "tunable functional materials", wherein the complementary geometry of the components and the choice of fullerene play crucial roles in defining the conductance properties. The highest electrical conductivity (σ = 1.3 × 10-8 S cm-1 at 298 K) was observed in the case of the C70-based SOF. In contrast, low conductivity was seen for the SOF based on pristine 2 (σ = 5.9 × 10-11 S cm-1 at 298 K). The conductivity seen for the C70-based SOF approaches that seen for other TTF- and fullerene-based supramolecular materials despite the fact that the present systems are metal-free and constructed entirely from neutral building blocks. Transient absorption spectroscopic measurements corroborated the formation of charge-transfer states (i.e., 2δ+/C60δ- and 2δ+/C70δ-, respectively) rather than fully charge separated states (i.e., 2•+/C60•- and 2•+/C70•-, respectively) both in solution (toluene and benzonitrile) and in the solid state at 298 K. Such findings are considered consistent with an ability to transfer charges effectively over long distances within the present SOFs, rather than, for example, the formation of energetically trapped ionic species.