Singly and Doubly N-Confused Calix[4]phyrin Organoplatinum(II) Complexes as Near-IR Triplet Sensitizers

Effect of Peripheral Functionalization of Pt(II) Porphyrin(2.1.2.1) on Singlet Oxygen Generation

Four structurally bent porphyrin(2.1.2.1) Pt(II) complexes have been obtained and verified well. Main absorbance of Pt(II) porphyrin(2.1.2.1) displayed a significant red-shift compared to that of porphyrin(1.1.1.1) Pt(II) molecules. 1O2 study indicated that electron-withdrawing group and intramolecular charge transfer effect synergistically endowed Pt(II) porphyrin(2.1.2.1) with good singlet oxygen-sensitizing capacity under blue LED light irradiation. This work presents a simple synthesis way to develop a new series of efficient porphyrinoid singlet oxygen photosensitizers for PDT through molecular engineering.

De novo fabrication of higher arene ring incorporated contorted calix[2]phyrin(2.2.1.1.1) and its F- bound complex

The rational design and synthesis of a novel contorted calix[2]phyrin(2.2.1.1.1) structure has been achieved, utilizing a terphenyl unit as a key building component. This terphenyl unit serves as a segment of the armchair periphery in a π-extended two-dimensional architecture. The resulting molecule exhibits remarkable properties, including the ability to self-assemble into solid-state supramolecular nanotubes. Additionally, it has demonstrated an affinity for complexation with fluoride anions, highlighting its potential for applications in molecular recognition and sensor technology. The incorporation of the terphenyl unit not only enhances the structural rigidity but also contributes to the unique electronic characteristics of the calix[2]phyrin.

The (o-p-o)-Terphenyl Embedded Calix[2]phyrin(2.2.1.1.1) and Its Cu(II) Complex

The introduction of a higher arene unit as a structural motif is unprecedented in calixphyrin chemistry. Herein, the syntheses, spectral and structural characterization of heretofore anonymous terphenylene unit (o-p-o) incorporated calixphyrin with fused sp2 meso carbons is reported. The explicitly tailored macrocyclic core is utilized to stabilize the Cu(II) metal ion. The molecular structures of the calixbenziphyrin and Cu(II) complex are unambiguously confirmed by single-crystal X-ray analysis. Moreover, theoretical supports uphold experimental conclusions.

Rational and controllable syntheses of variants of modified N-confused N-fused porphodimethenes and a porphotrimethene with adaptive properties

Retrosynthetic design and synthesis with structural isolation of two unprecedented core modified N-confused N-fused porphodimethene-like porphyrinoids possessing a [5.5.5.5] tetracyclic ring with tunable photophysical properties is reported. The solid-state X-ray crystal structure reveals the expected cis geometry for the meso-sp3 carbons. Controlled chemical oxidation of the porphodimethene analogue 11 bearing the N-confused pyrrole moiety to the corresponding porphotrimethene 12 has been achieved in quantitative yield, while 10 bearing the N-methyl N-confused pyrrole moiety remained unsusceptible to chemical oxidation. All three S2N3 hybrid N-confused N-fused porphodi(tri)methene-like porphyrinoids 10-12 could recognize the fluoride anion with high selectivity; however, porphodimethene 10 and porphotrimethene 12 do so via deprotonation rather than an anion recognition based mechanism as has been anticipated in the case of porphodimethene 11.

Porphyrin(2.1.2.1) organopalladium complexes as efficient singlet oxygen sensitizers

Four new non-planar and non-aromatic porphyrin organopalladium complexes were synthesized. Conformational structures and optical and electronic properties of the obtained organopalladium complexes containing meso-substituted phenyl, p-tert-butylphenyl, or pentafluorophenyl groups were fully investigated. These complexes showed potent capacity for singlet oxygen (1O2) generation under blue-light irradiation, and the 1O2 quantum yields were in the range of 41%-56%, which were comparable to that of Ru(bpy)3Cl2 (57%), and such potency made these organopalladium complexes potential 1O2 photo sensitizers for photodynamic therapy.

Oxygen quenching of structurally characterized [5,10,15,20-tetrakis(4-fluoro-2,6-dimethylphenyl)porphyrinato]platinum(II)

The compound [5,10,15,20-tetrakis(4-fluoro-2,6-dimethylphenyl)porphyrinato]platinum(II), [Pt(C52H40F4N4)] or Pt(II)TFP, has been synthesized and structurally characterized by single-crystal X-ray crystallography. The Pt porphyrin exhibits a long-lived phosphorescent excited state (τ0 = 66 µs), which has been characterized by transient absorption and emission spectroscopy. The phosphorescence is extremely sensitive to oxygen, as reflected by a quenching rate constant of 5.0 × 108 M-1 s-1, and as measured by Stern-Volmer quenching analysis.

Synthesis of novel zinc porphyrins with bioisosteric replacement of Sorafenib: Efficient theranostic agents for anti-cancer application

Novel zinc porphyrins (trans-A2B2 and A3B type) are reported containing pharmacophoric groups derived from Sorafenib at the meso-positions. The pharmacophoric and bioisosteric modification of Sorafenib was done with 2-methyl-4-nitro-N-phenylaniline. The in-vitro photo-cytotoxicity studies of zinc porphyrins on HeLa cells revealed excellent PDT based autophagy inhibition of cancer cells, with IC50 values between 6.2 to 15.4 μM. The trans-A2B2 type zinc porphyrin with two bioisosteric groups gave better cytotoxicity than A3B type. Molecular docking studies revealed excellent binding with mTOR protein kinase of the designed porphyrins. The confocal studies indicated significant ER localization of trans-A2B2 type zinc porphyrin in HeLa cells along with ROS generation. trans-A2B2 type zinc porphyrin induced ER stress in cancer cells, thereby causing elevation of Ca+2 ions in cytoplasm, which led to cancer cell death via autophagy pathway. The studies suggested that trans-A2B2 and A3B type zinc porphyrins can be developed as theranostic agents for anti-cancer applications.

Mapping the influence of ligand electronics on the spectroscopic and 1O2 sensitization characteristics of Pd(II) biladiene complexes bearing phenyl-alkynyl groups at the 2- and 18-positions

Photodynamic therapy (PDT) is a promising treatment for certain cancers that proceeds via sensitization of ground state 3O2 to generate reactive 1O2. Classic macrocyclic tetrapyrrole ligand scaffolds, such as porphyrins and phthalocyanines, have been studied in detail for their 1O2 photosensitization capabilities. Despite their compelling photophysics, these systems have been limited in PDT applications because of adverse biological side effects. Conversely, the development of non-traditional oligotetrapyrrole ligands metalated with palladium (Pd[DMBil1]) have established new candidates for PDT that display excellent biocompatibility. Herein, the synthesis, electrochemical, and photophysical characterization of a new family of 2,18-bis(phenylalkynyl)-substituted PdII 10,10-dimethyl-5,15-bis(pentafluorophenyl)-biladiene (Pd[DMBil2-R]) complexes is presented. These second generation biladienes feature extended conjugation relative to previously characterized PdII biladiene scaffolds (Pd[DMBil1]). We show that these new derivatives can be prepared in good yield and, that the electronic nature of the phenylalkynyl appendages dramatically influence the PdII biladiene photophysics. Extending the conjugation of the Pd[DMBil1] core through installation of phenylacetylene resulted in a ∼75 nm red-shift of the biladiene absorption spectrum into the phototherapeutic window (600-900 nm), while maintaining the PdII biladiene's steady-state spectroscopic 1O2 sensitization characteristics. Varying the electronics of the phenylalkyne groups via installation of electron donating or withdrawing groups dramatically influences the steady-state spectroscopic and photophysical properties of the resulting Pd[DMBil2-R] family of complexes. The most electron rich variants (Pd[DMBil2-N(CH3)2]) can absorb light as far red as ∼700 nm but suffer from significantly reduced ability to sensitize formation of 1O2. By contrast, Pd[DMBil2-R] derivatives bearing electron withdrawing functionalities (Pd[DMBil2-CN] and Pd[DMBil2-CF3]) display 1O2 quantum yields above 90%. The collection of results we report suggest that excited state charge transfer from more electron-rich phenyl-alkyne appendages to the electron deficient biladiene core circumvents triplet sensitization. The spectral and redox properties, as well as the triplet sensitization efficiency of each Pd[DMBil2-R] derivative is considered in relation to the Hammett value (σp) for each biladiene's R-group. More broadly, the results reported in this study clearly demonstrate that biladiene redox properties, spectral properties, and photophysics can be perturbed greatly by relatively minor alterations to biladiene structure.

Pd(II), Ni(II), and Cu(II) complexes of α,α'-ditolylmethanone dipyrroethene

Dipyrromethenes containing two pyrrole rings connected by one meso-carbon are versatile monoanionic bidentate ligands and form coordination complexes with many metals/nonmetals/metalloids. Dipyrroethenes containing one additional meso-carbon compared to dipyrromethenes have more space between coordinating pyrrole nitrogens and provide a good coordination environment but have not been explored as ligands in coordination chemistry. Dipyrroethenes are dianionic bidentate ligands and by suitable modifications, the coordination environment of dipyrroethenes can be changed further. Herein, we successfully synthesized α,α'-ditolylmethanone dipyrroethene which is a bipyrrolic tetradentate ligand with an ONNO ligand core and used it for the synthesis of novel Pd(II), Ni(II), and Cu(II) metal complexes by treating it with respective metal salts in CH₂Cl₂/CH₃OH at room temperature. The X-ray crystallographic structure of the metal complexes showed that the M(II) ion was coordinated to the ONNO atoms of the ligand in a perfect square planar geometry. The NMR studies of Pd(II) and Ni(II) complexes also supported the highly symmetric nature of the metal complexes. The absorption spectra of the metal complexes showed strong bands in the region of 300-550 nm. The electrochemical studies of metal complexes revealed that only ligand-based oxidation and reduction were observed. The DFT and TD-DFT studies were in agreement with the experimental observations. Our preliminary studies indicated that the Pd(II) complex can be used as a catalyst for the Fujiwara-Moritani olefination reaction.

Organometallic chemistry confined within a porphyrin-like framework

The world of modified porphyrins changed forever when an N-confused porphyrin (NCP), a porphyrin isomer, was first published in 1994. The replacement of one inner nitrogen with a carbon atom revolutionised the chemistry that one is able to perform within the coordination cavity. One could explore new pathways in the organometallic chemistry of porphyrins by forcing a carbon fragment from the ring or an inner substituent to sit close to an inserted metal ion. Since the NCP discovery, a series of modifications became available to tune the coordination properties of the cavity, introducing a fascinating realm of carbaporphyrins. The review surveys all possible carbatetraphyrins(1.1.1.1) and their spectacular coordination and organometallic chemistry.

Synthesis and Properties of Stable 20π Porphyrinoids

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins and differ from porphyrins in aromaticity which in turn affects the structure, properties and chemical reactivities. Research over the years indicated that the 20π porphyrinoids can be stabilized as non-aromatic/anti-aromatic or Mobius aromatic macrocycles using different strategies such as core-modification of porphyrins, non-metal/metal complexation of porphyrins, peripheral modification of porphyrins and expanded porphyrinoids. The structural properties such as aromaticity of the macrocycle can be controlled by choosing the right synthetic strategy. This review will provide an overview of the development in the chemistry of 20π porphyrinoids giving emphasize on the synthesis, structure and electronic properties of these macrocycles which have huge potential for various applications.

Metalloceneincorporated Hybrid Singly N-Methyl N-Confused Calixphyrins: Synthesis, Characterization, Protonation and Deprotonation Studies

Rational design and isolation of two hitherto unknown highly stable single conformer of ferrocene incorporated meso-aryl substituted singly N-methyl N-confused-calixphyrins have been achieved in quantitative yields. The solid-state crystal structure reveals the obvious trans-geometry for the meso-protons with the possibility for both the macrocycles to exist either racemic or enantiomer forms. However, thorough solution-state spectroscopic characterization strongly concludes the experimental isolation of a single isomer for both the macrocycles. The drastic modification of UV-vis spectral patterns upon imine pyrrole N protonation and amine pyrrole NH deprotonation of both the calixphyrins could pave way for these macrocycles to act as opto-electronic materials. The conformational preorganization and protonation and deprotonation induced conformational reorganization have been extensively studied by solution state spectroscopic techniques, solid state X-ray crystal structure and in depth DFT level theoretical calculations.

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Tailor-made aromatic porphyrinoids with NIR absorption

The highlight of this article is the recent progress in the state-of-the-art synthetic design and isolation of artificial porphyrinoids by swapping pyrrole component(s) with diverse functionalized pyrrolic(heterocyclic)/carbacycle building block(s) to compare the impact on the electronic absorption spectra and aromaticity of the incorporated isomeric/expanded porphyrinoids. Attention has been directed towards five distinct criteria of utilizing functionalized pyrrolic(heterocyclic)/aromatic hydrocarbons as synthons for NIR absorbing aromatic isomeric (N-confusion)/expanded porphyrinoids (with five/six heterocycles): (i) fused or annelated pyrrole (heterocycle), (ii) functionalized bi-pyrrole/bi-thiophene/bi-furan building blocks, (iii) azulene based carbacycle building block, (iv) vinylogous aromatic carbacycle/heterocycle(s) building block and (v) N-confused pyrrole ring(s), and N-confused fused pyrrole ring(s) leading to π-extension. These hybrid porphyrinoids are ideal candidates for basic research into macrocyclic aromaticity and for many potential applications owing to NIR absorption.

Synthesis, computational and optical studies of tetraphenylethene-linked Pd(ii)dipyrrinato complexes

A series of Pd(ii)dipyrrinato complexes are synthesized and characterized. Their DFT and aggregation studies and photo-catalytic applications are reported.

Luminescent Iridium(III) Dipyrrinato Complexes: Synthesis, X-ray Structures, DFT and Photocytotoxicity Studies of Glycosylated Derivatives

A series of luminescent Ir(III) dipyrrinato complexes were synthesized having various aromatic chromophores on the C-5 position of dipyrrin ligand. The presence of different chromophores on the Ir(III) dipyrrinato complexes...

Structural isolation of NIR absorbing ferrocenyl bridged N-confused fused expanded phlorin, N-confused porphodimethene and the π-extended corrorin isomer: synthesis and characterization

Concise syntheses and spectroscopic, solid state X-ray crystal structure and theoretical studies of three electronically appealing new generation hitherto unknown ferrocenyl bridged N-confused heterocyclic macrocycles with (without) fusion are reported. Intriguingly, the expanded N-confused fused phlorin (1.1.1.1.1) with the built-in tripentacyclic [5.5.5] moiety exhibits tailing of the NIR absorption band beyond 1000 nm while the nonconjugated porphodimethene and a new generation π-extended isomeric corrorin analogue exhibit UV-vis absorption.

Syntheses of thiophene appended N-confused phlorin isomers

A doubly confused thiapentapyrrane NSP-5 was synthesized by acid-catalysed condensation. Subsequent oxidation with DDQ did not afford the expected thiasapphyrin-like product. Instead, two tetrapyrrolic macrocycles, i.e. neo-N-confused phlorin (1) and N-confused phlorin-II (2) were obtained in the yields of 14% and 18%, respectively. The compounds were characterized by NMR, HRMS, and X-ray diffraction analyses. Single crystal structures clearly reveal that the thienyl units are not embedded into the macrocycles, but appended as meso-substituents, and the C[Formula: see text]-N and C[Formula: see text]-C[Formula: see text] cyclization modes can be clearly revealed by the crystal structures of 1 and 2, respectively. The observation that the thienyl unit is not involved in oxidative cyclization may be related to the relatively low reactivity of the thiophene moiety compared with the more electron-rich pyrrole unit. These results indicate that oxidative cyclization of linear thiaoligopyrranes containing terminal thiophene units may be developed as an effective approach for synthesizing nonconjugated macrocycles like phlorin analogues.

Unraveling the Photodynamic Activity of Cationic Benzoporphyrin-Based Photosensitizers against Bladder Cancer Cells

In this study, we report the preparation of new mono-charged benzoporphyrin complexes by reaction of the appropriate neutral benzoporphyrin with (2,2'-bipyridine)dichloroplatinum(II) and of the analogs' derivatives synthesized through alkylation of the neutral scaffold with iodomethane. All derivatives were incorporated into polyvinylpyrrolidone (PVP) micelles. The ability of the resultant formulations to generate reactive oxygen species was evaluated, mainly the singlet oxygen formation. Then, the capability of the PVP formulations to act as photosensitizers against bladder cancer cells was assessed. Some of the studied formulations were the most active photosensitizers causing a decrease in HT-1376 cells' viability. This creates an avenue to further studies related to bladder cancer cells.

Neo-Porphyrinoids: New Members of the Porphyrinoid Family

The four pyrrole rings and four meso carbons of tetrapyrrolic porphyrins can be arranged in different ways and the resulting porphyrin isomers exhibit very distinct electronic properties. The extensive research carried out on the porphyrins over the years has revealed that porphyrin can have several possible isomers and some of these have been identified and synthesized. Among the porphyrin isomers synthesized so far, porphycene and N-confused porphyrins have been investigated extensively whereas the other porphyrin isomers such as hemiporphycene, corrphycene and isoporphycene remain underdeveloped because of synthetic difficulties and their inherently unstable nature. Neoporphyrinoids are new members of the porphyrinoid family that were discovered serendipitously in 2011. Neoporphyrinoids are structural analogues of porphyrinoids with a confused pyrrole nitrogen linked to a meso carbon or the adjacent pyrrole carbon. Thus, neoporphyrinoids have an unusual structure in which pyrrole N is a part of a porphyrinoid framework and the lone pair of electrons on nitrogen participate in macrocyclic conjugation. It's been a decade since the discovery and different types of neoporphyrinoids, including regular, contracted and expanded neoporphyrinoids, have been synthesized by rational synthetic methodologies and their spectral, structural, aromatic and coordination properties have been studied. There is huge scope to develop different synthetic routes to produce new types of stable neoporphyrinoids to study their properties and potential applications. This article presents a brief overview of the synthesis, structure and properties of the neoporphyrinoids reported in this decade.

meso-Carbazole substituted palladium porphyrins: Efficient catalysts for visible light induced oxidation of aldehydes

The A3B and A2B2 type porphyrins having [Formula: see text]-butylcarbazole and [Formula: see text]-cyanophenyl groups are synthesized and characterized. Their palladium complexes have also been prepared and utilized as catalysts for the photo-oxidation reactions of aromatic aldehydes in good yields. Pd(II)porphyrins displayed decent phosphorescence at [Formula: see text]670 nm and were able to generate singlet oxygen upon light irradiation. The calculated singlet oxygen quantum yields for Pd(II)porphyrins were between 57% and 73%. The photo-catalytic application of Pd(II)porphyrins for aerobic oxidation of aromatic aldehydes is demonstrated.

3-D Cryptand Like Normal and Doubly N-Confused Calixbenzophyrins: Synthesis and Structural Studies

The three-dimensional (3-D) cryptand-like normal and doubly-N-confused calixbenzophyrins embedded with phenyl rings in the macrocyclic skeleton are successfully synthesized from single starting materials. These structural isomers are characterized by spectral studies and unambiguously confirmed by crystal analyses.

Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt(II) Complexes with Aromatic Alkynyl Ligands

The synthesis of five novel cyclometalated platinum(II) compounds containing five different alkynyl-chromophores was achieved by the reaction of the previously synthesized Pt-Cl cyclometalated compound (1) with the corresponding RC≡CH by a Sonogashira reaction. It was observed that the spectral and photophysical characteristics of the cyclometalated platinum(II) complexes (Pt-Ar) are essentially associated with the platinum-cyclometalated unit. Room-temperature emission of the Pt-Ar complexes was attributed to phosphorescence in agreement with DFT calculations. Broad nanosecond (ns)-transient absorption spectra were observed with decays approximately identical to those obtained from the emission of the triplet state. From the femtosecond-transient absorption (fs-TA) data, two main excited-state decay components were identified: one in the order of a few picoseconds was assigned to fast intersystem crossing to populate the triplet excited-state and the second (hundreds of ns) was associated with the decay of the transient triplet state. In general, efficient singlet oxygen photosensitization quantum yields were observed from the triplet state of these complexes.

Synthesis of Water-Soluble Thioglycosylated trans-A2B2 Type Porphyrins: Cellular Uptake Studies and Photodynamic Efficiency

The synthesis of water-soluble thioglycosylated A₂B₂ type porphyrins and their zinc(II) complexes is reported. The water-soluble trans-A₂B₂ porphyrins were synthesized in two steps, via [2+2] condensation between thioglycosylated dipyrromethanes and aromatic aldehydes in 15-21% yields. The thioglycosylated trans-A₂B₂ porphyrins showed decent in vitro singlet oxygen generation, which was supported by the intracellular DCFDA study. The in vitro cellular investigations of thioglycosylated A₂B₂ porphyrins were carried out in lung cancer cells (A549) to test their photodynamic therapeutic (PDT) activity. The PDT study revealed significant cytotoxicities of porphyrins with IC₅₀ values between 23.3 and 44.2 μM in the dark, whereas, after visible light exposure, the photosensitizers exhibited IC₅₀ values around 11.1-23.8 μM. The water-soluble thioglycosylated zinc(II) porphyrins having two meso-N-butylcarbazole groups exhibited an excellent degree of photocytotoxicity (IC₅₀ = 4.6-8.8 μM). The flow cytometry analysis revealed that cellular uptake and ROS (reactive oxygen species) generation efficiency of water-soluble thioglycosylated zinc(II) porphyrins were considerably higher than nonmetalated porphyrins. Confocal microscopy images displayed substantial distribution in the endoplasmic reticulum with partial colocalization in mitochondria and lysosomes of water-soluble thioglycosylated zinc(II) porphyrins in A549 cells.

Photooxidation Reactions of Cyclometalated Palladium(II) and Platinum(II) Complexes

New C,N,S-cyclometalated palladium(II) and platinum(II) complexes have been synthesized and their structural, electrochemical, and photochemical properties examined. The blue color of these complexes in solution changed to yellow under visible-light irradiation. By measurement of the absorption spectra for quantifying changes in color, isosbestic points for each complex clearly indicated the presence of only two species responsible for the change of color. X-ray analysis revealed that the visible-light-induced yellow species were S-oxygenated sulfinato complexes. Photosensitized generation of singlet oxygen (¹O₂) was confirmed by the direct detection of singlet oxygen luminescence at 1275 nm. The present cyclometalated palladium(II) and platinum(II) complexes are efficient photosensitizers of singlet oxygen, which rapidly reacts with coordinating sulfur atoms.

meso-Aryl substituted stable unorthodox 5,10-porphodimethenes with α,β and β,β-N-methyl pyrrole connectivities: synthesis and spectroscopic, solid state and theoretical characterization

meso-Aryl substituted highly stable single conformers of doubly mutant porphodimethenes.

Cationic axial ligands on sulfur substituted silicon(iv) phthalocyanines: improved hydrophilicity and exceptionally red-shifted absorption into the NIR region

Herein, we report the exceptionally red-shifted absorption of sulfur-substituted silicon(iv) phthalocyanines upon introduction of cationic axial ligands.

Functional Calixphyrins: Synthetic Strategies and Applications

Calixphyrins are hybrid macrocycles that contain both sp²- and sp³-hybridized carbon atoms and hence bear analogy to both porphyrins and calixpyrroles. Due to the presence of sp³-hybridized carbon atoms, π-conjugation is disrupted in calixphyrins, which leads to conformational flexibility. Hence, these molecules find a use in anion binding, host-guest chemistry and metal-coordination chemistry. During the last decade, studies on calixphyrins have been a topic of wide interest to researchers. Various functionalities have been introduced to the structure of calixphyrins, leading to the development of expanded calixphyrins, core-modified calixphyrins and N-confused calixphyrins with diverse applications. This review outlines the detailed historical origin of the synthesis of calixphyrins with emphasis on current research and development in this area. The modular syntheses of normal calixphyrins, expanded calixphyrins, core-modified calixphyrins and N-confused calixphyrins are also discussed, along with their applicative aspects.