Far-red fluorescence and chiroptical properties of pyrrolopyrrole aza-BODIPYs induced by the B,O-chelation.

A titanium-mediated aza-BODIPY synthesis using diketopyrrolopyrrole bearing o-anisyl substituents provided B,O-chelated pyrrolopyrrole aza-BODIPYs in a one-pot manner via ether bond cleavage and chelation of the resulting nucleophilic oxygen to the boron atom. The B,O-chelation not only induces the redshifts of absorption and fluorescence but also endows chiroptical properties.

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.

One-pot synthesis of azabora[6]helicene by a Schiff base forming reaction.

Azabora[6]helicene as a new heterohelicene analogue was synthesized by a one-pot reaction of commercially available 2,6-diaminopyridine and benzo[c,d]indole-2(1H)-one and subsequent boron coordination. While the single-crystal X-ray diffraction analysis elucidated a helical structure in the solid state, a dynamic helicity inversion was observed in solution.

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.

Synthesis, Structural, and Optical Properties of Azuleno[1,2-c]pyran-1-ones: BroÌ·nsted Acid-Mediated Cyclization of 2-Azulenylalkynes.

Pyrones and their aromatic ring-fused derivatives have gained significant attention due to their diverse biological activities and potential as foundational frameworks for advanced materials. In this paper, we describe a proficient approach for the preparation of azuleno[1,2-c]pyran-1-ones, which are difficult to produce by using conventional methods. The synthesis was achieved through BroÌ·nsted acid-mediated cyclization of 2-azulenylalkynes. The structural and optical properties of azuleno[1,2-c]pyran-1-ones were characterized by single-crystal X-ray analysis, NMR, UV/vis, and fluorescence spectroscopies. Under acidic conditions, these compounds displayed notable spectral alterations and emission, distinct from their spectra in neutral medium. These results suggest that azuleno[1,2-c]pyran-1-ones hold great potential for applications in organic electronic materials and fluorescent pH sensors.

Oxidation of 5,15-Dioxaporphyrin: Its Generality and Novelty as an Oxaporphyrin Analogue.

5,15-Dioxaporphyrin (DOP) is a novel meso-oxaporphyrin analogue and exhibits unique 20π-antiaromaticity, unlike its mother congener of 18π-aromatic 5-oxaporphyrin, commonly known as its cationic iron complex called verdohem, which is a key intermediate of heme catabolism. To reveal its reactivities and properties as an oxaporphyrin analogue, the oxidation of tetra-ß-arylated DOP (DOP-Ar4 ) was explored in this study. Stepwise oxidation from the 20π-electron neutral state was achieved, and the corresponding 19π-electron radical cation and 18π-electron dication were characterized. Further oxidation of the 18π-aromatic dication resulted in the formation of a ring-opened dipyrrindione product by hydrolysis. Considering a similar reaction of verdoheme to ring-opened biliverdin in the heme degradation in nature, the current result consolidates the ring-opening reactivity of oxaporphyrinium cation species.

Substituent effects on paratropicity and diatropicity in π-extended hexapyrrolohexaazacoronene.

Research into the application of antiaromatic compounds as molecular materials is an attractive strategy in the development of electronic materials. Antiaromatic compounds have traditionally been considered to be unstable, and thus, the creation of stable antiaromatic compounds has been sought in the field of organic chemistry. Recently, some studies have been reported on the synthesis, isolation, and elucidation of the physical properties of compounds with stability and definitive antiaromatic properties. In general, antiaromatic compounds are considered to be more susceptible to substituents due to their inherently narrow HOMO-LUMO gap compared to aromatic compounds. However, there have been no studies examining substituent effects in antiaromatic compounds. In this study, we have developed a synthetic method to introduce various substituents into π-extended hexapyrrolohexaazacoronene (homoHPHAC+), one of the stable and clearly antiaromatic compounds, and investigated the substituent effects on the optical, redox, and geometrical properties and paratropicity of a series of compounds. In addition, the properties of the two-electron oxidized form, homoHPHAC3+, were investigated. Control of electronic properties by introducing substituents into antiaromatic compounds provides a new design guideline for molecular materials.

Pyrrole-Fused Azacoronene Analog with Sulfur Embedded in the Outer Periphery.

The synthesis of sulfur-embedded hexapyrrolohexaazacoronene (HPHAC) analog 2 and its corresponding desulfurized and rearranged compounds was achieved from tetrafluoroisothianaphthene. Structures of all the new π-skeletons were determined by X-ray crystallography. Comparison of the electronic spectrum of 2 with those of its derivatives revealed less involvement of the sulfur atom in π-conjugation. Similar to the reference HPHAC (1), compound 2 and its derivatives exhibited reversible oxidation behavior. The aromaticity of both neutral and dication states has been investigated through DFT calculations.

Synthesis of Peripherally Annulated Phenanthroporphyrins.

Synthesis of unusual phenanthroporphyrins was achieved by a stepwise precursor method. Precursor porphyrins fused with aryl-substituted bicyclo[2.2.2]octadiene afforded the corresponding arylbenzoporphyrins (arylBPs) by a retro Diels-Alder reaction. Unusual phenanthroporphyrins were obtained via the intramolecular Scholl reaction of arylBPs. X-ray crystallographic analysis revealed a distorted, helical porphyrin plane. Red-shifted absorptions of tetraphenanthroporphyrin are observed at ca. 580 nm for the B band and at 700-900 nm for the Q bands. Analysis of magnetic circular dichroism spectra and time-dependent density functional theory calculations was used to explain the optical properties and electronic structures.

Post-Modification of Pyrrolopyrrole Aza-BODIPY toward High Near-Infrared Fluorescence Brightness.

Pyrrolopyrrole aza-BODIPYs (PPABs), dimeric aza-BODIPY analogues, exhibit intense absorption and fluorescence in the visible and near-infrared (NIR) regions. Here, we developed a facile postmodification by palladium-catalyzed coupling reactions to synthesize a series of donor-acceptor-donor (D-A-D) PPABs. Despite the possible fluorescence quenching dictated by the energy-gap low, D-A-D PPABs exhibit high-fluorescence brightness in the NIR region, implying their potential use as a bright NIR emitter.

Synthetic Model for FRET Constructed from Covalently Linked Porphyrin Dimers through a Pyrene Bridge.

We report the synthesis and characterization of two porphyrin arrays C6F5-PyZnDP and Mes-PyZnDP covalently linked by a pyrene moiety which differs from their substituents at their meso-positions. The key precursor bis-dipyrromethane linked with a pyrene bridge was prepared by the acid-catalyzed condensation of pyrene-1,6-dialdehyde with excess pyrrole. The synthesis of C6F5-PyZnDP was carried out via two different synthetic routes, with one being efficient over the other. Therefore, the superior route was employed for the synthesis of C6F5-PyZnDP and Mes-PyZnDP. Both the free base and metalated diporphyrins show bathochromically shifted absorption and intense red emission due to the extended π-conjugation through pyrene and porphyrins. The single-crystal X-ray structure reveals an orthogonal orientation of pyrene in between the two planar porphyrins and a slipped stacked packing arrangement in the crystal structure with large meso-meso distances. DFT analysis of both the ground state and the excited S1 state of the macrocycles indicates the difference in the HOMO and LUMO contribution in both the states arising from slight twisting from the mean orthogonal position in the excited state. Further, the Förster energy transfer (FRET) efficiencies from pyrene (donor) to the covalently linked Zn-porphyrins (acceptor) are estimated to be 85 and 91% for Mes-PyZnDP and C6F5-PyZnDP, respectively.

Synthesis, Structure, and Optical Properties of a Bis-Macrocycle Derived from a Highly Emissive 1,3,6,8-Tetra(1H-pyrrol-2-yl)pyrene.

A tetra-functionalized pyrene precursor 4b is prepared using the Suzuki-Miyaura coupling of 1,3,6,8-tetrabromopyrene with N-Boc-2-pyrroleboronic acid. 4b displayed a blue emission with a high quantum yield (ϕF = 0.89). 4b is subjected to [3 + 2] Lewis acid-catalyzed condensation with 2,2'-bithiophene-dialcohol 5, affording a planar bis-N2S2 internally linked with pyrene. The single-crystal X-ray structure of bis-N2S2 revealed a planar conformation with all of the pyrrolic nitrogens and thiophenic sulfurs pointing toward the macrocyclic core. Further, the reduction of bis-N2S2 was attempted in the presence of Zn/NH4Cl at room temperature in CHCl3. A sharp color change from pink to brown was observed presumably due to the formation of its reduced congener bis-N2S2-2H. However, the reduced species was found to revert back to its oxidized form over a period of 25 min in CHCl3. Density functional theory (DFT) studies reveal that the two monocyclic halves of bis-N2S2-2H exhibit differences in aromaticity depending on amino and imino pyrroles present inside each individual core. Such a conversion was also monitored by ultraviolet-visible (UV-vis) absorption spectral studies, and the exact composition of bis-N2S2-2H was confirmed by High-resolution/mass spectrometry (HR/MS) analysis. Experimental and theoretical studies reveal a weak aromatic character of bis-N2S2 due to the absence of global conjugation.

Spontaneous Assembly and Three-Dimensional Stacking of Antiaromatic 5,15-Dioxaporphyrin on HOPG.

Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO-LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso-2-thienyl-substituted 5,15-dioxaporphyrin (DOP-1) is scrutinized at the liquid-solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations >0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO-LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.

Cumulative risk of developing a new symptom in patients with primary biliary cholangitis and its impact on prognosis.

Background and Aim: Symptoms of primary biliary cholangitis (PBC) frequently impair one's quality of life (QOL). Nonetheless, with improved treatment, the prognosis of PBC also improves. QOL plays an important role in patients with PBC. In this study, we aimed to reevaluate the transition of new symptom development in PBC and its predictive factors. Methods: This retrospective multicenter study enrolled 382 patients with PBC for symptom analysis. The impact of a newly developed symptom on PBC prognosis was investigated by Kaplan-Meier analysis with propensity score matching and logistic progression analysis. Results: The cumulative risk of developing a new symptom after 10 and 20 years of follow-up was 7.6 and 28.2%, and specifically that of pruritus, which was the most common symptom, was 6.7 and 23.3%, respectively. In Cox hazard risk analysis, serum Alb level (hazard ratio [HR], 1.097; 95% confidence interval [CI], 1.033-1.165; P = 0.002), the serum D-Bil level (HR, 6.262; 95% CI, 2.522-15.553, P < 0.001), and Paris II criteria (HR, 0.435; 95% CI, 0.183-1.036; P = 0.037) were significant independent predictors of a new symptom. Kaplan-Meier analysis showed that the overall survival and liver-related death were not significant between patients with and without a new symptom. Conclusion: The cumulative risk of new symptom development is roughly 30% 20 years after diagnosis and could be predicted by factors including serum albumin levels, serum D-Bil level, and Paris II criteria.

Tropo(thio)ne-embedded homoHPHACs: does the tropylium cation induce global antiaromaticity in expanded hexapyrrolohexaazacoronene?

Tropo(thio)ne-embedded homoHPHACs and their dications were synthesised by an electrophilic annulation of secoHPHAC and successive oxidation. 13C NMR spectra of the dications represented global 22π homoaromaticity via homoconjugation, while alkylation of a thiocarbonyl-bridged homoHPHAC produced a 24π antiaromatic monocation.

Luminescent iridium(III) dipyrrinato complexes: synthesis, X-ray structures, and DFT and photocytotoxicity studies of glycosylated derivatives.

A series of luminescent Ir(III) dipyrrinato complexes were synthesized having various aromatic chromophores at the C-5 position of dipyrrin ligands. The presence of different chromophores on the Ir(III) dipyrrinato complexes altered their optical properties and produced strong emission in the red to NIR region (680-900 nm) with huge Stokes shifts (5910-7045 cm-1). TD-DFT studies indicated significant charge distribution between dipyrrin ligands and Ir-cyclometalated units in all the molecules. X-ray crystal structures revealed an octahedral geometry of the Ir(III) center in the complex. The in vitro studies of the glycosylated Ir(III) complexes revealed strong photoluminescence with maximum Stokes shifts, and they showed significant photocytotoxicity in skin keratinocyte (HaCaT) and lung adenocarcinoma (A549) cells. The singlet oxygen generation quantum yields of glycosylated Ir(III) complexes were in the range of 70-78% in water. The estimated IC50 values were between 17 and 25 µM after light exposure, and confocal microscopy revealed significant localization of the glycosylated Ir(III) complexes in the endoplasmic reticulum (ER) of cancer cells. The neutral Ir(III) dipyrrinato complexes are promising tracking agents for cellular imaging in the biological window and for photodynamic therapy (PDT) applications.

Synthesis, Properties, and Packing Structures of Wing-Shaped N-Doped Nanographene in Various Oxidation States.

A rigid wing-shaped bicyclo[2.2.2]octadiene-fused bis-hexapyrrolohexaazacoronene (HPHAC) is synthesized, and subsequent chemical oxidation affords a stable biradical dication and an aromatic tetracation. The physicochemical properties and single-crystal structures in various oxidation states are characterized. The face-to-face π-stacked dimeric structures are observed in the neutral and dicationic states. The HPHAC flakes can act as aromatic walls in a tetracation state, producing enlarged induced magnetic shielding space through the superimposition effect.

Synthesis of Non- or Antiaromatic Dicarbaamethyrin: [24]Diazulihexaphyrin(0.1.0.0.1.0).

A "3+3" condensation reaction of 1,3-di(2-pyrrolyl)azulene with aryl aldehyde followed by an oxidative aromatization afforded diazuliamethyrin, [24]diazulihexaphyrin(0.1.0.0.1.0). X-ray diffraction analysis revealed a relatively planar structure of diprotonated diazuliamethyrin with a mean plane deviation of 0.37 Å. A 24π non- or antiaromatic character was confirmed by 1H NMR, absorption, MCD spectra, and TD-DFT calculations that included the NICS values and ACID plots.

Disruption of Antiaromaticity in Structurally Related Expanded Porphyrin-like Macrocycles with Benzene Linkers.

1,4-Phenylene-linked cyclotrimer (3T) and cyclotetramer (4T) have been synthesized via Lewis acid-catalyzed self-condensation of appropriate precursors. Structural and Density Functional Theory (DFT) studies reveal the disruption of annulenic conjugation in both 3T and 4T by linking phenylene rings prevented them from global antiaromaticity. The single crystal X-ray structure of 4T reveals all the nitrogens are pointing toward the macrocyclic core with near-planar and square-shaped geometry, thus in sharp contrast to the ring-strained conformation of 3T.

Janus Pyrrolopyrrole Aza-dipyrrin: Hydrogen-Bonded Assemblies and Slow Magnetic Relaxation of the Cobalt(II) Complex in the Solid State.

A novel pyrrolopyrrole azadipyrrin (Janus-PPAD) with Janus duality was synthesized by a Schiff base-forming reaction of diketopyrrolopyrrole. The orthogonal interactions of the hydrogen-bonding ketopyrrole and metal-coordinating azadipyrrin moieties in Janus-PPAD enabled the metal ions to be arranged at regular intervals: zinc(II) and cobalt(II) coordination provided metal-coordinated Janus-PPAD dimers, which can subsequently form hydrogen-bonded one-dimensional arrays both in solution and in the solid state. The supramolecular assembly of the zinc(II) complex in solution was investigated by 1 H NMR spectroscopy based on the isodesmic model, in which a binding constant for the elongation of assemblies is constant. Owing to the tetrahedral coordination, in the solid state, the cobalt(II) complex exhibited a slow magnetic relaxation due to the negative D value of -27.1 cm-1 with an effective relaxation energy barrier Ueff of 38.0 cm-1 . The effect of magnetic dilution on the relaxation behavior is discussed. The relaxation mechanism at low temperature was analyzed by considering spin lattice interactions and quantum tunneling effects. The easy-axis magnetic anisotropy was confirmed, and the relevant wave functions were obtained by ab initio CASSCF calculations.