Electronic structures, bonding aspects and photophysical properties of N-heterocyclic carbene manganese complexes: DFT and TDDFT exploration

Here we explored the influence of axial ligands on the structural, electronic, and photophysical properties of Mn(II)(TPP)(1,3-Me2Imd)(L) complexes, where L = -NH3, -OCH3, -SH, -Cl, and -NO2, using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Frontier molecular orbital analysis was performed to assess the reactivity behavior of the complexes which exhibit strong nonlinear optical properties due to their high polarizability. The nature of bonding and charge distribution was further investigated through electrostatic potential mapping, quantum theory of atoms in molecules, electron localization function and localized orbital locator analyses. Natural bond orbital analysis was also conducted to identify stabilizing interactions within the species. Our calculations reveal that the complex with an NH3 axial ligand (species 1) possesses a larger HOMO-LUMO energy gap and a more negative electrostatic potential, suggesting lower reactivity due to the electron-donating character of the ligand. Furthermore, TDDFT results indicate strong light-harvesting efficiencies in the visible region (575-735 nm), with species 4 demonstrating the highest efficiency and species 5 the lowest. These findings provide insights into the design of Mn-based complexes for optoelectronic applications.

Donor-acceptor mixed-ligand MOF with energy transfer-mediated high-efficiency singlet oxygen generation for boosted organic photosynthesis

Integrating energy donor and acceptor chromophores as ligands within one MOF for advanced artificial photosynthesis is of great interest but appears to be a major challenge. Herein, via a simple one-pot synthetic strategy, an energy acceptor porphyrin ligand 5,15-di(p-benzoato)porphyrin (H2DPBP) was successfully integrated into an energy donor 1,4-naphthalenedicarboxylic acid (H2NDC)-based MOF (UiO-66-NDC) to construct a mixed-ligand MOF, donated as UiO-66-NDC-H2DPBP. Benefiting from the ample overlap between the emission spectrum of H2NDC and the absorption spectrum of H2DPBP, an efficient energy transfer (EnT) process from the donor H2NDC to the acceptor H2DPBP within UiO-66-NDC-H2DPBP can occur and be captured by time-resolved spectroscopy. Furthermore, the singlet oxygen (1O2) generation efficiency of UiO-66-NDC-H2DPBP mediated by this EnT process as well as the EnT process from the triplet state (T1) of the photosensitizer H2DPBP ligand to the ground state of molecular oxygen (3O2) upon light irradiation can be maximized via simply regulating the loading amount of H2DPBP, leading to boosted photocatalytic activities toward important aerobic oxidation reactions of amines and sulfides, even under sunlight and ambient air. This work explores an avenue to construct high-efficiency energy donor and acceptor-based light-harvesting systems by utilizing mixed-ligand MOFs as platforms to advanced artificial photosynthesis.

Fully Conjugated Thiophene-Fused Oligo-BODIPYs: A Class of Intensely Near-Infrared Absorbing, Arc-Shaped Materials with up to 31 Linearly-Fused Rings

Structurally well-defined large π-conjugated systems attract significant interest in molecular materials both for their unique electronic/photophysical properties and unexplored structure-property relationships arising from synthetic challenges. Herein, we address this challenge by leveraging a series of polycondensed π-system doping with B, N and S heteroatoms. In our approach, a series of fully conjugated thiophene-fused oligo-BODIPYs with atomic precision have been efficiently synthesized through the combination of intermolecular SNAr reactions followed by intramolecular aromatic oxidative couplings from halogenated BODIPY precursors. The largest architecture is a fully fused BODIPY octamer, featuring a coplanar backbone of 31 linearly fused rings. The extended π-conjugation causes a dramatic shift of the absorption event from about 500 nm (monomer) to 822 nm (octamer) with extremely high molar absorptivities reaching 800,000 M-1 cm-1, as well as maintaining intense fluorescence intensity (ΦFL up to 0.32), long triplet lifetime (τT = 0.61-15.4 μs), efficient triplet quantum yields (ΦT = 0.24-0.81) and good singlet oxygen generation abilities. More interestingly, due to the weak aromaticity of thiophene, oligo-BODIPYs exhibit triplet state localization as their conjugation length increases, where the triplet energy remains constant while the singlet energy decreases significantly. Notably, intense near-infrared thermally activated delayed fluorescence (TADF) is observed even in tetramers, hexamers, and octamers. Our findings not only present a new series of heteroatom-doped condensed π-systems but also establish a precise regulation mechanism for singlet-triplet energy levels in molecules with large rigid π-conjugated structures. Furthermore, this work provides a novel strategy for designing next-generation TADF molecules with narrowband emission.

Au-Acyclic Diaminocarbene-Linked Porphyrin Covalent Organic Framework as a Cascade Catalyst for Photocatalytic Sulfide Oxidation and Intermolecular Nucleophilic Addition

The design and synthesis of a multifunctional covalent organic framework (COF) for various applications have been considered a big challenge. Herein, we report the construction of a novel porphyrin-based Au-acyclic diaminocarbene (Au-ADC)-linked COF (abbreviated as Au-ADC-Por-COF) via a metal-mediated nucleophilic addition reaction. The resultant multifunctional Au-ADC-Por-COF revealed an outstanding performance in a cascade catalyzing photocatalytic sulfide oxidation under visible-light irradiation and intermolecular nucleophilic addition. This research might open a new way for the design of advanced materials with unprecedented structures and catalytic activities.

Efficient Ammonia Electrosynthesis from Pure Nitrate Reduction via Tuning Bimetallic Sites in Redox-Active Covalent Organic Frameworks

Electrocatalytic nitrate reduction reaction (NITRR) represents a promising approach for ammonia synthesis, but existing application has been constrained by the complex proton-coupled electron transfer and the sluggish kinetics induced by various intermediates. Herein, we synthesized a series of metalized covalent organic frameworks: NiTP-MTAPP MCOFs (M = 2H, Co, Cu, and Fe), based on dual redox-active centers: thiophene-substituted Ni-bis(dithiolene) ligand-Ni[C2S2(C4H2SCHO)2]2 and metallic porphyrin. Through regulating the adsorption and desorption of species at the catalytic sites, we have identified the optimal NITRR electrocatalyst: NiTP-CoTAPP MCOF, which achieved the highest faradaic efficiency (FE) of approximately 85.6% at -0.8 V (vs. RHE) in pure nitrate solution, with an impressive yield rate of 160.2 mmol h-1 g-1 cat. The generation of active hydrogen at [NiS4] sites achieved dynamic equilibrium with the timely hydrogenation reaction at CoN4 sites, effectively suppressing the hydrogen evolution reaction. Moreover, the incorporation of thiophene (TP) groups and metal ions facilitates charge transfer. Density functional theory (DFT) calculations demonstrated the reduction in energy barriers at different catalytic sites. The CoN4-NiS4 system exhibited the optimal adsorption-to-desorption capability and the lowest energy barrier (0.58 eV) for the rate-determining step (*NO → *HNO), which is supported by the moderate d-band center and Bader charge value.

Electron Shuttling in High-Valent Heterobimetallic NiFe-Porphyrin Dimers: Stabilization of Ni(III) and Fe-Phenoxyl Radicals

A series of axially phenoxide-bound Ni(II)-Fe(III) heterobimetallic porphyrin dimers, as a synthetic mimic of the diheme enzyme MauG, have been synthesized, which upon 4e- oxidations revealed the oxidized complex involving porphyrin π-cation radicals, an Fe(III)-coordinated phenoxyl radical, and a Ni(III) center. Redox cooperativity and the extensive π-conjugation through the bridge make the oxidized complex behave like a single supramolecular entity having unpaired electrons spread over five magnetic centers. Several isoelectronic states for the oxidized Fe(por) center, i.e., Fe(IV)(por)(PhO•) ↔ Fe(IV)(por•+)(PhO) ↔ Fe(III)(por•+)(PhO•), are possible that can be in equilibrium with low-energy barriers between them. DFT studies demonstrate spin delocalization with a dramatic change in the Fe-OTyr bond upon oxidation, which thereby becomes an active modulator of various electronic states of high-valent intermediates in diheme enzymes, such as MauG and bacterial diheme cytochrome c peroxidase (bCcP), for their function.

Heterole-Fused [20]- and [22]Smaragdyrins and Fused-Heterole-Bridged [20]- and [22]Smaragdyrin Dimers

In order to examine the effects of the fused heterole on the electronic properties of aromatic and antiaromatic smaragdyrins, 2,3-thiophene- and 2,3-indole-fused [20]smaragdyrins were synthesized by Suzuki-Miyaura coupling and subsequent oxidative fusion reaction, and were reduced with NaBH4 to the corresponding [22]smaragdyrins. Fused-thiophene- and fused-pyrrole-bridged [20]- and [22]smaragdyrin dimers were also synthesized in the similar manner. The installed fused heteroles mitigate the paratropic ring current of the [20]smaragdyrin but exert only minor effects on the diatropic ring current of the [22]smaragdyrin. Similar features are also observed for the fused-heterole-bridged [20]- and [22]smaragdyrin dimers.

Panchromatic PAH-Porphyrin Hybrids with a Step-Wise Increasing π-System

The rational synthesis of three β-meso-fused porphyrins with a step-wise increasing π-system size is presented. The synthetic route, which introduces a five-membered ring between the macrocycle and an aromatic fragment, is modular in its nature and proceeds straightforwardly. The well-soluble conjugates have intriguing optical properties, namely bathochromically shifted and flattened absorption curves. Density functional theory (DFT) calculations provide insights into the electronic structure and transitions, unveiling small HOMO-LUMO gaps.

Modulation of Photophysical Properties of N-Confused Hexaphyrins through Carbon-Metal Bonding and Structural Modifications─A Theoretical Insight

To understand the influence of N-confusion and C-M bonding on the absorption characteristics of expanded metalloporphyrins, the structural, electronic, and optical properties of N-confused hexaphyrin(1.1.1.1.1.1) bis-metal complexes (7-PdAu and 7-PtAu) were investigated by employing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Our findings demonstrate that forming C-M bonds leads to a saddle-shaped hexaphyrin structure, enhancing the metal-ligand interaction compared to O-M bonds. This structural alteration results in reduced aromaticity and a narrowing of the HOMO-LUMO gap, along with a significant bathochromic shift in the electronic absorption spectrum. Notably, the 7-PdAu and 7-PtAu complexes exhibit pronounced absorption bands beyond 1100 nm, indicating their potential as candidates for near-infrared (NIR) phototherapeutic and optoelectronic applications. Overall, this work underscores the synergistic effects of N-confusion and carbon-metal bonding in tuning the photophysical properties of porphyrin-based systems, paving the way for advanced applications in photonics.

Meso-β, β-β' trifused porphyrins: synthesis, spectral, electrochemical and DFT studies and their femtosecond third-order nonlinear optical properties

Meso-β, β-β' trifused porphyrins incorporating two distinct active methylene groups (MN = malononitrile and IND = 1,3-indanedione) and their corresponding metal complexes with Cu(II) and Zn(II) have been synthesized with good to excellent yields and characterized by various spectroscopic techniques and spectrometric methods. Single crystal X-ray analysis of the Zn(II) complex ZnTFPMB(MN)2 (where TFP = trifused porphyrin and MB = mono benzo) revealed a ruffled nonplanar 'armchair' type conformation with a twist angle of 24.10°. The absorption spectra showed a significant bathochromic shift in both the B- and Q-bands, extending into the near-infrared (NIR) region, particularly for π-extended trifused porphyrins. The cyclic voltammograms of MN-appended trifused porphyrins revealed unusual redox behavior, likely due to chemical reactions occurring at the electrode surface during electroreduction. The HOMO-LUMO energy gap for the π-extended porphyrins (MTFPMB(VCN)2) was effectively reduced to ≤1.5 V, compared to ∼2.23 V for the parent porphyrins. Additionally, the femtosecond third-order nonlinear optical properties of the synthesized trifused porphyrins and reported Ni(II) complexes were investigated using the Z-scan technique. Most of the studied porphyrins exhibited promising three-photon absorption coefficients and cross-section values, suggesting their potential applications in optical limiting, bio-imaging, and advanced optoelectronics.

Dimerization of Hexaphyrin with an Appendant Pyrrole Possessing a Reactive Site to Alleviate the Steric Hindrance

Oxidative dimerization of π-conjugated molecules is a straightforward approach for effectively extending π-conjugation and absorption features. However, it is challenging to construct dimeric species of bulky π-conjugated frameworks because of the steric hindrances and/or poor regioselectivity. To address these issues, a pyrrole unit has been regioselectively appended to the α position of N-confused hexaphyrin (1.1.1.1.1.0) 1 by a facile acid-catalyzed condensation reaction, leading to the formation of pyrrole-appendant 2. Subsequent oxidation of 2 yielded an inner-fused monomer 2F and two fused dimeric species, namely, (2F)2a and (2F)2b. In contrast, oxidation of the corresponding Ni(II) complex 2Ni generated dimer (2Ni)2. Subsequent demetalation resulted in the formation of bipyrrole-linked freebase dimer (2)2, which could chelate Ni(II) and Cu(II) ions to furnish complexes (2Ni)2 and (2Cu)2, respectively. In comparison to the fused dimeric species (2F)2a and (2F)2b, the nonfused dimer (2)2 and its complexes (2Ni)2 and (2Cu)2 exhibit diminished local aromaticity, narrowed HOMO-LUMO gaps, and a red-shifted absorption profile that extends up to 2200 nm. These findings underscore a potent strategy for creating expanded porphyrin dimers, wherein the aromaticity and near-infrared absorption can be fine-tuned by incorporating an appendant pyrrole unit.

Controllable Self-Assembly of V═O Metalloradical Complex with Intramolecular Charge Transfer for Enhanced NIR-II Fluorescence Imaging-Guided Photothermal Therapy

Near-infrared second region (NIR-II) fluorescence imaging provides enhanced tissue penetration, achieving efficient NIR-II fluorescence and photoacoustic imaging (PA)-guided photothermal therapy (PTT) all in one material remains a challenging yet promising approach in cancer treatment. Herein, open-shell V═O metalloradical complex (VONc) is self-assembled into VONc nanospheres (VONc NPs). VONc NPs exhibit light absorption from 300 to 1400 nm, fluorescence spectra ranging from 900 to 1400 nm, and a distinct fluorescence signal even at 1550 nm. Moreover, VONc NPs exhibit outstanding photostability and a higher photothermal conversion efficiency of 46.6% than that of closed-shell zinc naphthalocyanine nanorods (ZnNc NRs). V═O centered metalloradical serves as transient electron-withdrawing groups to facilitate charge transfer (CT), introducing additional nonradiative energy dissipation pathways and enhancing efficient heat generation. In vitro experiments of VONc NPs indicate that a highly effective photothermal action causes harm to both mitochondria and lysosomes, resulting in the death of tumor cells, closed-shell ZnNc NPs exhibit almost no cell killing as contrast. In vivo anti-tumor therapy results of VONc NPs demonstrate excellent NIR-II fluorescence imaging-guided PTT against tumors with a favorable biosafety profile. "Centered metalloradical boosting CT" toward open-shell metal complexes provides significant insight for developing single-material integrated nanosystems for diagnostic and therapeutic applications.

Molecular Aharonov-Bohm-type interferometers based on porphyrin nanorings

A goal of molecular electronics and spintronics is to create molecular devices that change their conductance in response to external stimuli. The Aharonov-Bohm (AB) effect implies that an electronic device formed from a quantum ring and metallic leads will exhibit such behavior under external magnetic fields. At first sight, it appears that unrealistically large fields would be required to significantly alter the conductance of a molecular ring. However, the sensitivity of a molecular AB interferometer to magnetic fields can be increased by weakening the coupling between the molecular ring and the metallic leads. An ideal molecular ring for an AB interferometer has a large radius (to encompass a larger fraction of the AB flux quantum), and a small effective mass (high electron mobility) to enhance its response to magnetic fields. Here, we use computational modelling to demonstrate that recently synthesized zinc porphyrin nanorings, with radii of 2-9 nm, could behave as molecular AB interferometers at achievable magnetic field strengths (5-10 T), if weak ring-lead coupling is used. Building on our recently developed semi-empirical approach, which incorporates the effects of finite magnetic fields on the electronic structure, we develop a transport computational platform that allows us to identify sharp Fano resonances in the transmittance probability of porphyrin nanorings that could be exploited to control the current with an applied magnetic field. These resonances are rationalized in terms of a magnetic field-induced delocalization of the molecular orbitals. Our findings indicate that molecular AB interferometry should be feasible with current experimental capabilities.

Activatable Porphyrin-Based Sensors, Photosensitizers and Combination Therapeutics

Porphyrins, known as the "pigments of life", have evolved from their natural roles into versatile tools for biomedical applications. The development of activatable porphyrins has significantly expanded their utility, enabling precise responses to a carefully selected target analyte. These advances have broadened their use in imaging, diagnosis, and therapy. These capabilities are driven by activity-based sensing (ABS), which enhances the selectivity and sensitivity to various disease biomarkers. However, their design and implementation are intrinsically complex. This perspective provides an easy-to-follow roadmap that details how such molecules can be developed. Furthermore, we highlight recent progress in ABS-modified porphyrins, focusing on how specific modifications achieve these remarkable properties across various biomedical platforms. The ongoing evolution of activatable porphyrins holds great promise for the development of sophisticated, responsive systems, offering more effective diagnostic and therapeutic tools.

β-meso-Fused pyrene-porphyrin scaffolds with panchromatic absorption features

The π-extension of porphyrins with pyrenes through the β-meso-fusion of five-membered rings is demonstrated. Three architectures resulting from combining up to two porphyrins and pyrenes were obtained straightforwardly in good overall yields. Although significantly planarized, the molecules retain excellent solubility and processability. Spectroscopic characterization and density-functional theory calculations reveal intriguing absorption features.

A Poly(2,7-anthrylene) with peri-Fused Porphyrin Edges

Anthracene has served as an important building block of conjugated polymers with the connecting positions playing a crucial role for the electronic structures. Herein, anthracene units have been coupled through their 2,7-carbons to develop an unprecedented, conjugated polymer, namely, poly(2,7-anthrylene) featuring additional peri-fused porphyrin edges. The synthesis starts from a 2,7-dibromo-9-nickel(II) porphyrinyl-anthracene as the pivotal precursor. Polymerization is achieved by an AA-type Yamamoto coupling, followed by a polymer-analogous oxidative cyclodehydrogenation to obtain a peri-fusion between porphyrin and anthracene moieties. Although further cyclodehydrogenation between the repeating units cannot be achieved in solution, the thermal treatment of the precursor polymer derived from 2,7-dibromo-9-porphyrinyl-anthracene on a metal surface realizes the full cyclodehydrogenation. The difference between solution and on-surface reactivity can be rationalized by the larger dihedral angle between repeat units in solution, which is reduced under the pronounced interaction with the metal surface. The peri-fusion in the title polymer gives rise to a narrow electronic band gap optical absorptions extending far into the near-infrared region. Oligomeric models are synthesized as well to support the analyses of the electronic and photophysical properties.

A Doubly meso-α Linked N-Confused Porphyrin Tape Silver(III) Complex Comprising an Antiaromatic Pyrrolo[2,3-f]indole Segment

The free base form of doubly meso-α linked N-confused porphyrin (NCP) tape 3 was successfully synthesized via Ir(I) mediated intramolecular coupling. The following silver complexation afforded the Ag(III) complex of doubly meso-α linked NCP tape 4. While 3 exhibited 38π aromatic characters, 4 exhibited not only 18π aromatic NCP-type characteristics but also a decent antiaromatic contribution of 12π pyrrolo[2,3-f]indole segment, as probed by NMR spectra, absorption spectra, and DFT calculations.

Solution Versus On-Surface Synthesis of Peripherally Oxygen-Annulated Porphyrins through C-O Bond Formation

This study investigates the synthesis of tetra- and octa-O-fused porphyrinoids employing an oxidative O-annulation approach through C-H activation. Despite encountering challenges such as overoxidation and instability in conventional solution protocols, successful synthesis was achieved on Au(111) surfaces under ultra-high vacuum (UHV) conditions. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and non-contact atomic force microscopy elucidated the preferential formation of pyran moieties via C-O bond formation and subsequent self-assembly driven by C-H⋅⋅⋅O interactions. Furthermore, the O-annulation process was found to reduce the HOMO-LUMO gap by lifting the HOMO energy level, with the effect rising upon increasing the number of embedded O-atoms.

A Review on Recent Trends in Photo-Drug Efficiency of Advanced Biomaterials in Photodynamic Therapy of Cancer

Photodynamic Therapy (PDT) has emerged as a highly efficient and non-invasive cancer treatment, which is crucial considering the significant global mortality rates associated with cancer. The effectiveness of PDT primarily relies on the quality of the photosensitizers employed. When exposed to appropriate light irradiation, these photosensitizers absorb energy and transition to an excited state, eventually transferring energy to nearby molecules and generating Reactive Oxygen Species (ROS), including singlet oxygen [1O2]. The ability to absorb light in visible and nearinfrared wavelengths makes porphyrins and derivatives useful photosensitizers for PDT. Chemically, Porphyrins, composed of tetra-pyrrole structures connected by four methylene groups, represent the typical photosensitizers. The limited water solubility and bio-stability of porphyrin photosensitizers and their non-specific tumor-targeting properties hinder PDT effectiveness and clinical applications. Therefore, a wide range of modification and functionalization techniques have been used to maximize PDT efficiency and develop multidimensional porphyrin-based functional materials. Recent progress in porphyrin-based functional materials has been investigated in this review paper, focusing on two main aspects including the development of porphyrinic amphiphiles that improve water solubility and biocompatibility, and the design of porphyrin-based polymers, including block copolymers with covalent bonds and supramolecular polymers with noncovalent bonds, which provide versatile platforms for PDT applications. The development of porphyrin-based functional materials will allow researchers to significantly expand PDT applications for cancer therapy by opening up new opportunities. With these innovations, porphyrins will overcome their limitations and push PDT to the forefront of cancer treatment options.

Oxidations of (2,2'-Diphenyl)ethylidene-Bridged Porphyrin Dimers

Oxidation reactions of (2,2'-diphenyl)ethylidene-bridged porphyrin dimers were examined for the synthesis of (2,2'-diphenyl)ethylidene-inserted porphyrin arch tape dimers. These reactions provided, in addition to the target arch tape dimers, unexpected products such as a bicyclo[3.3.0]octane-fused porphyrin dimer, a (2,2'-fluorenyl)ethylidene-inserted porphyrin arch tape dimer, and a meso- and ortho-phenyl-linked free base dimer, depending upon the substrate and reaction conditions, demonstrating the high promise of these porphyrin substrates. The target arch tape dimers, which were synthesized by the oxidation with DDQ and CF3SO3H, exhibit red-shifted and enhanced Q-bands and small electrochemical HOMO-LUMO gaps, indicating effective conjugation.

The third-order nonlinear optical responses of zinc porphyrin oligomers: Cycles vs linear chains

Porphyrins are widely used as potential nonlinear optical (NLO) materials because of their highly delocalized π electrons and feasible synthesis and functionalization with broad biological applications. A variety of linear and cyclic porphyrin derivatives have been synthesized, and the correlation between their structures and NLO properties awaits being disclosed. In this work, the electronic structures and third-order NLO properties of linear and cyclic butadiyne-linked zinc porphyrin oligomers have been studied by quantum chemical methods and sum-over-states model. The static second hyperpolarizability (<γ0>) increases exponentially with the number of zinc porphyrin units ([<γ0>n] = 0.67[<γ0>1]n2.63, n = 2 ∼ 6) in linear π-conjugated oligomers, and the <γ0> of the linear hexamer is about 74 times that of the monomer. Such enhancement of <γ0> in linear oligomers originates from closely-lying frontier molecular orbitals available for low energy electron excitations and strong charge transfer-based excitations across porphyrins. The <γ0>s of cyclic porphyrins are lower than that of the linear hexamer, though the interaction between the ring and the ligand enhances the <γ0> of some cyclic zinc porphyrin complexes. The large two-photon absorption cross sections confer on these zinc porphyrin derivatives excellent candidates for two-photon absorption applications.

Fused Aromatic and Antiaromatic Smaragdyrin Dimers

Singly-linked aromatic [22]smaragdyrin BF2 complex dimer was synthesized by the reductive coupling of 16-brominated [22]smaragdyrin BF2 complex, which was oxidized to a stable diradical with PbO2. As the first example of fused smaragdyrin dimer, a fused [22]smaragdyrin BF2 complex dimer was synthesized by the oxidation of a CuCl-BF2 complex dimer with FeCl3 and subsequent reduction with NaBH4. After removal of the BF2 group, the singly-linked and fused aromatic dimers were oxidized to the corresponding antiaromatic [20]smaragdyrin free base dimers. The first oxidation and reduction potentials of these dimers are split depending upon the intramolecular electronic interactions, which are larger for the fused dimers. Despite the large electronic interactions, the aromatic and antiaromatic characters are well preserved in the fused dimers.

Development and validation of polymer-based porphyrin-incorporated reference materials for calibration of quantitative light-induced fluorescence device

BACKGROUND

This study aimed at developing and validating polymer-based reference materials with varying amounts of porphyrin to accurately assess and calibrate quantitative light-induced fluorescence (QLF) device.

METHODS

Reference materials with porphyrin concentrations ranging from 0 to 0.08 wt.% were prepared. The surface properties of the materials were analyzed via gloss and roughness measurements. Color analysis of the specimens was performed on black and white backgrounds with or without filters using a spectrophotometer. This approach revealed the correlations between fluorescence and color. The fluorescence emitted by the specimens was analyzed by measuring ΔR and ΔRmax values using a QLF-D Biluminator™.

RESULTS

The surface gloss and roughness of the reference materials were not affected by the porphyrin content (p > 0.005). Spectrophotometric measurements revealed significant color differences among most specimen groups depending on the background color and the presence of a filter. QLF-D imaging revealed significant differences in fluorescence (ΔR and ΔRmax) among all specimen groups regardless of the background. The fluorescence values observed on the black backgrounds were higher than those observed on the white backgrounds (p < 0.05).

CONCLUSIONS

The developed polymer-based porphyrin-incorporated materials serve as reliable reference standards for accurate assessment and calibration of QLF devices. This study demonstrates the importance of background conditions in fluorescence detection and highlights the potential of these materials as standards for QLF device calibration.

Fused Hexabenzocoronene-Porphyrin Conjugates with Tailorable Excited-State Lifetimes

A new clear-cut strategy for fusing N-heterocyclic and carbon-pure systems is introduced en route to a versatile platform of multi-purpose tetrapyrrolic chromophores. In particular, three novel C-C bond-fused porphyrin-hexabenzocoronene (HBC) conjugates were synthesized under oxidative cyclodehydrogenation conditions, starting from tailor-made nickel porphyrin precursors. The fusion of the individual aromatic systems via 5-membered rings led to highly soluble π-extended porphyrins in excellent yields. The resulting porphyrin-HBC conjugates exhibit absorption cross-sections that are of interdisciplinary interest in the ever-growing field of organic photovoltaics and near-infrared (NIR) dyes. Quantum chemical calculations show that the newly formed 5-membered rings induce biradicaloid character in the porphyrin core, which has a strong impact on excited state lifetimes. This is confirmed by a thorough optoelectronic and time-resolved characterization in order to understand these unique features better. Broadened absorption characteristics go hand-in-hand with short-lived excited states with up to six orders of magnitude faster decay rates.

β-to-β Singly Linked Subphthalocyanine Dimers with Effective π-Conjugation

In this work, a series of π-conjugated Subphthalocyanine dimers assembled by simple π-bridges were efficiently synthesized through metal-catalyzed reactions. Despite being singly linked, these readily accessible arrays exhibit excellent π-electron communication, significantly perturbing the orbital distribution of conventional SubPcs and inducing notable alterations in their optical properties. The findings presented here demonstrate the potential of SubPcs for constructing curved porphyrin arrays with well-conjugated skeletons and intriguing functionalities.

Incorporating Zinc Metal Sites in Aluminum-Coordinated Porphyrin Metal-Organic Frameworks for Enhanced Photocatalytic Nitrogen Reduction to Ammonia

Rationally designing photocatalysts is crucial for the solar-driven nitrogen reduction reaction (NRR) due to the stable N≡N triple bond. Metal-organic frameworks (MOFs) are considered promising candidates but suffer from insufficient active sites and inferior charge transport. Herein, it is demonstrated that incorporating 3d metal ions, such as zinc (Zn) or iron (Fe) ions, into Al-coordinated porphyrin MOFs (Al-PMOFs) enables the enhanced ammonia yield of 88.7 and 65.0 µg gcat -1 h-1, 2.5- and 1.8-fold increase compared to the pristine Al-PMOF (35.4 µg gcat -1 h-1), respectively. The origin of ammonia (NH3) is verified via isotopic labeling experiments. Incorporating Zn or Fe into Al-PMOF generates active sites in Al-PMOF, that is, Zn-N4 or Fe-N4 sites, which not only facilitates the adsorption and activation of N2 molecules but suppresses the charge recombination. Photophysical and theoretical studies further reveal the upshift of the lowest unoccupied molecular orbital (LUMO) level to a more energetic position upon inserting 3d metal ions (with a more significant shift in Zn than Fe). The promoted nitrogen activation, suppressed charge recombination, and more negative LUMO levels in Al-PMOF(3d metal) contribute to a higher photocatalytic activity than pristine Al-PMOF. This work provides a promising strategy for designing photocatalysts for efficient solar-to-chemical conversion.

Electronic and magnetic properties of porphyrin nanoribbons with chelated metals

Advances in surface-assisted synthesis routes now allow for precise control in the preparation and modification of low-dimensional structures. The choice of molecular precursors plays a fundamental role in these processes since the structural details and properties of the resulting nanostructures directly depend on the molecular block used. From this perspective, units based on porphyrins have proven to be promising candidates for the construction of nanosystems with nontrivial geometry. In particular, efforts have been made to synthesize different arrangements of π-conjugated porphyrins. With this motivation, we use computational simulations to investigate the electronic and magnetic properties of nanoribbons constructed from the concatenation of π-extended porphyrins hosting transition metal atoms. We show that the binding energy of these systems and the specific way the electrons populate the d-shells are strongly influenced by the type of the transition metal. Furthermore, it was observed that most systems with chelated metals (except Ni and Zn) feature magnetic properties. The systems considered in this work have analogs in finite structures recently synthesized in the laboratory so the nanomaterials proposed here have a high potential to be produced in the near future.

Modeling-driven materials by design for conjugated polymers: insights into optoelectronic, conformational, and thermomechanical properties

Conjugated polymers (CPs) have emerged as pivotal functional materials in the realm of flexible electronics and optoelectronic devices due to their unique blend of mechanical flexibility, solution processability, and tunable optoelectronic properties. This review synthesizes the latest molecular simulation-driven insights obtained from various multiscale modeling techniques, including quantum mechanics (QM), all-atomistic (AA) molecular dynamics (MD), coarse-grained (CG) modeling, and machine learning (ML), to elucidate the optoelectronic, structural, and thermomechanical properties of CPs. By integrating findings from our recent computational work with key experimental studies, we highlight the molecular mechanisms influencing the multifunctional performance of CPs. This comprehensive understanding aims to guide future research directions and applications in the modeling assisted design of high-performance CP-based materials and devices.

Aromaticity in the Spectroscopic Spotlight of Hexaphyrins

Spectroscopic properties are commonly used in the experimental evaluation of ground- and excited-state aromaticity in expanded porphyrins. Herein, we investigate if the defining photophysical properties still hold for a diverse set of hexaphyrins with varying redox states, topologies, peripheral substitutions, and core-modifications. By combining TD-DFT calculations with several aromaticity descriptors and chemical compound space maps, the intricate interplay between structural planarity, aromaticity, and absorption spectra is elucidated. Our results emphasize that the general assumption that antiaromatic porphyrinoids exhibit significantly attenuated absorption bands as compared to aromatic counterparts does not hold even for the unsubstituted hexaphyrin macrocycles. To connect the spectroscopic properties to the hexaphyrins' aromaticity behaviour, we analyzed chemical compound space maps defined by the various aromaticity indices. The intensity of the Q-band is not well described by the macrocyclic aromaticity. Instead, the degeneracy of the frontier molecular orbitals, the HOMO-LUMO gap, and the |ΔHOMO-ΔLUMO|2 values appear to be better indicators to identify hexaphyrins with enhanced light-absorbing abilities in the near-infrared region. Regions with highly planar hexaphyrin structures, both aromatic and antiaromatic, are characterized by an intense B-band. Hence, we advise using a combination of global and local aromaticity descriptors rooted in different criteria to assess the aromaticity of expanded porphyrins instead of solely relying on the absorption spectra.

Bridge vs Terminal Cyano-coordination in Binuclear Cobalt Porphyrin Dimers: Interplay of Electrons between Metal and Ligand and Spin-Coupling via Bridge

Three cyano-coordinated cobalt porphyrin dimers were synthesized and thoroughly characterized. The X-ray structure of the complexes reveals that cyanide binds in a terminal fashion in both the anti and trans isomers of ethane- and ethylene-bridged cobalt porphyrin dimers, while in the cis ethylene-bridged dimer, cyanides bind in both terminal and bridging modes. The nonconjugated ethane-bridged complex stabilizes exclusively a diamagnetic metal-centered oxidation of type CoIII(por)(CN)2 both in the solid and in solution. In contrast, the complexes with the conjugated ethylene-bridge contain signatures of both paramagnetic ligand-centered oxidation of the type CoII(por•+)(CN)2 and diamagnetic metal-centered oxidation of type CoIII(por)(CN)2 with the metal-centered oxidized species being the major component in the solid state as observed in XPS, while the ligand-centered oxidized species are present in a significant amount in solution. 1H NMR spectrum in solution displays two set of signals corresponding to the simultaneous presence of both the diamagnetic and paramagnetic species. EPR and magnetic investigation reveal that there is a moderate ferromagnetic coupling between the unpaired electrons of the low-spin CoII center and the porphyrin π-cation radical in CoII(por•+)(CN)2 species as well as an antiferromagnetic coupling between the two CoII(por•+) units through the ethylene and CN bridges.

Synergistic meso-β regulation of porphyrins: squeezing the band gap into the near-infrared I/II region

The development of novel near-infrared (NIR) materials with extremely small energy gaps and high stability is highly desirable in bioimaging and phototherapy. Here we report an effective strategy for narrowing the energy gaps of porphyrins by synergistic regulation of meso/β substituents. The novel NIR absorbing/emitting meso-alkynyl naphthoporphyrins (Zn-TNP and Pt-TNP) are synthesized via the retro-Diels-Alder reaction. X-ray crystallography analysis confirms the highly distorted structures of the complexes. Both compounds exhibit intense Q bands around 800 nm, while Zn-TNP shows deep NIR fluorescence at 847 nm. Pt-TNP displays NIR-II room temperature phosphorescence peaking at 1106 nm with an extremely large Stokes shift of 314 nm, which are the longest wavelengths observed among the reported platinum porphyrinoids. Furthermore, Pt-TNP shows remarkable photostability and a notable capacity for synchronous singlet oxygen and heat generation under NIR light irradiation, demonstrating potential in combined photodynamic/photothermal therapy. A theoretical analysis reveals the progressive lifting of the HOMO by the β-fused benzene ring, the decrease of the LUMO upon meso-alkynyl substitution, and energy-releasing pathways varying with metal ions. This dual regulation approach demonstrates great promise in designing innovative multifunctional NIR porphyrin materials.

Directly-Fused Ni(II)Porphyrin Conjugated Polymers with Blocked meso-Positions: Impact on Electrocatalytic Properties

The oxidative coupling reaction of two Ni(II) porphyrins meso-substituted with three and four phenyl groups, Ni(II) 5,10,15-(triphenyl)porphyrin (NiPh3P) and Ni(II) 5,10,15,20-(tetraphenyl)porphyrin (NiPh4P) respectively, was investigated in a oxidative chemical vapor deposition (oCVD) process. Irrespective of the number of meso-substituents, high-resolution mass spectrometry evidences the formation of oligomeric species containing up to five porphyrin units. UV-Vis-NIR and XPS analyses of the oCVD films highlighted a strong dependence of the intermolecular coupling reaction with the substrate temperature. Specifically, higher substrate temperatures yield lowering of valence band maxima and reduction of the band gap. The formation of conjugated polymeric assemblies results in increased conductivities as compared to their sublimed counterparts. Yet, electrocatalytic measurements exhibit water oxidation onset overpotentials (308 mV for pNiPh3P and 343 mV for pNiPh4P) comparatively higher than the onset overpotential measured for the oCVD film from Ni(II) 5,15-(diphenyl)porphyrin (pNiPh2P), i. e. 283 mV. Although DFT and comparative oCVD studies suggest the formation of directly fused porphyrins involving 'phenyl-mediated' and β-β linkages when reacting tetra-meso-substituted porphyrins, the present findings highlight that multiple direct fusion (β-β/meso-meso/β-β or meso-β/β-meso) is essential for Ni(II) porphyrin-based conjugated polymers to enable a dinuclear radical oxo-coupling operating mechanism for water oxidation at low overpotential and durable catalytic activity.

A Triply Linked Copper(III) Dicarbacorrole Dimer

A triply linked dicarbacorrole dimer (7) was synthesized from a new meso-meso singly linked dicarbacorrole dimer precursor (6) via an oxidative fusion reaction by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in the presence of trifluoromethanesulfonic acid (TfOH). Single crystal X-ray structure of 7 adopts a flat conformation with a length as ca. 15.946 Å and a width as 6.903 Å, which can be regarded as a short carbaporphyrinoid tape. Two coordinated Cu ions keeps the +3 oxidation state in 7, as confirmed by NMR spectroscopy, single crystal X-ray diffraction and X-ray photoelectron spectroscopy (XPS). This is in sharp contrast to the Osuka's triply linked tetrapyrrolic corrole dimers, where the inner 3NH form is not stable and thus can only act as a divalent ligand. Due to the non-aromatic nature of dicarbacorrole macrocycle, the largely decreased HOMO-LUMO gap and red-shifted absorption of 7 are best ascribed to the strong electronic interaction between two dipyrromethene-type chromophores. To our knowledge, this is the first fully fused carbaporphyrinoid dimer with β-β, meso-meso, β-β triply linkages prepared to date.

On-Surface Synthesis of Polyene-Linked Porphyrin Cooligomer

π-Conjugated molecules are viewed as fundamental components in forthcoming molecular nanoelectronics in which semiconducting functional units are linked to each other via metallic molecular wires. However, it is still challenging to construct such block cooligomers on the surface. Here, we present a synthesis of [18]-polyene-linked Zn-porphyrin cooligomers via a two-step reaction of the alkyl groups on Cu(111) and Cu(110). Nonyl groups (-C9H19) substituted at the 5,15-meso positions of Zn-porphyrin were first transformed to alkenyl groups (-C9H10) by dehydrogenation. Subsequently, homocoupling of the terminal -CH2 groups resulted in the formation of extended [18]-polyene-linked porphyrin cooligomers. The structures of the products at each reaction step were investigated by bond-resolved scanning tunneling microscopy at low temperatures. A combination of angle-resolved photoemission spectroscopy and density functional theory calculations revealed the metallic property of the all trans [18]-polyene linker on Cu(110). This finding may provide an approach to fabricate complex nanocarbon structures on the surface.

Vibronic Coupling Drives the Ultrafast Internal Conversion in a Functionalized Free-Base Porphyrin

Internal conversion (IC) is a common radiationless transition in polyatomic molecules. Theory predicts that molecular vibrations assist IC between excited states, and ultrafast experiments can provide insight into their structure-function relationship. Here we elucidate the dynamics of the vibrational modes driving the IC process within the Q band of a functionalized porphyrin molecule. Through a combination of ultrafast multidimensional spectroscopies and theoretical modeling, we observe a 60 fs Qy-Qx IC and demonstrate that it is driven by the interplay among multiple high-frequency modes. Notably, we identify 1510 cm-1 as the leading tuning mode that brings the porphyrin to an optimal geometry for energy surface crossing. By employing coherent wave packet analysis, we highlight a set of short-lived vibrations (1200-1400 cm-1), promoting the IC within ≈60 fs. Furthermore, we identify one coupling mode (1350 cm-1) that is responsible for vibronic mixing within the Q states. Our findings indicate that porphyrin-core functionalization modulates IC effectively, offering new opportunities in photocatalysis and optoelectronics.

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.

A Triply Linked Porphyrin-Norcorrole Hybrid with Singlet Diradical Character

Norcorrole Ni(II) complexes have recently received considerable attention because they are readily accessible antiaromatic molecules. Their high stability under ambient conditions and ease of synthesis have enabled the exploration of the intrinsic properties of antiaromatic molecules. Here, we report the synthesis and properties of meso-meso singly linked porphyrin-norcorrole hybrids and a triply linked porphyrin-norcorrole hybrid. The singly linked and triply linked porphyrin-norcorrole hybrids were fully characterized, including an X-ray structural analysis. Due to their orthogonal conformation, the singly linked hybrids maintain the individual electronic properties of their porphyrin and norcorrole subunits, while the triply linked hybrid shows a significantly smaller electrochemical HOMO-LUMO gap (0.45 eV) than that of Ni(II) dimesitylnorcorrole (1.08 eV). Furthermore, the triply linked hybrid exhibits singlet diradical characteristics, as confirmed by VT NMR, ESR, and SQUID experiments.

Recent Developments in Porphyrin-Based Metal-Organic Framework Materials for Water Remediation under Visible-Light Irradiation

Access to clean drinking water is a basic requirement, and eliminating pollutants from wastewater is important for saving water ecosystems. The porous structure and surface characteristics of metal-organic frameworks (MOFs) can function as a perfect scaffold for removing toxic compounds from wastewater. Porphyrins are promising building blocks for constructing MOFs. Porphyrin-based metal-organic frameworks (P-MOFs) have been fabricated using porphyrin ligands, metal clusters, or ions. These materials can harvest light from a wide region of the solar spectrum, and their framework morphology and physicochemical properties can be controlled by changing their peripheral subunits or metal ions. These porous crystalline materials have generated interest because of their distinctive characteristics, including large permanent porosity, interesting surface morphology, broad conformational diversity, high photostability, and semiconducting nature. This article discusses the recent progress and usefulness of P-MOFs. The fabrication procedures of P-MOFs are discussed, followed by the adsorptive and photocatalytic removal of contaminants from wastewater. The relationships between the geometries of P-MOFs and their light-harvesting and charge-transfer mechanisms for the photocatalytic degradation of pollutants are highlighted. Finally, some future perspectives and obstacles in the photodegradation usage of P-MOFs are discussed, along with feasible research directions to standardize efficient photocatalysts for improved photodegradation for water treatment.

Synthesis of Pyrrole-Sharing Fused Porphyrinoid Hybrids by Post-fabrication of Ni(II) Porphyrins

Pyrrole-sharing fused hybrids of NiII porphyrin with PdII N-confused(NC)-corrole and PdII NC-oxaporphyrin were synthesized by post-fabrication of NiII porphyrins. Specifically this consists of Friedel-Crafts type aromatic substitution reaction of meso-free NiII porphyrin with α,α'-dibromotripyrrin and Pd(OAc)2 assisted cyclization, and final heating to induce a Pd-C bond formation. NiII porphyrins fused with PdII NC-corrole and with PdII NC-oxaporphyrins show coplanar structures with a shared pyrrole unit. In these hybrids, the PdII NC-oxaporphyrin is aromatic and the PdII NC-corrole is moderately antiaromatic and these local electronic properties interact to influence the whole network.

Deducing the conformational space for an octa-proline helix

A molecular dyad, PY-P8-PER, comprising a proline octamer sandwiched between pyrene and perylene terminals has been synthesized in order to address the dynamics of electronic energy transfer (EET) along the oligo-proline chain. A simple pyrene-based control compound equipped with a bis-proline attachment serves as a reference for spectroscopic studies. The N-H NMR signal at the terminal pyrene allows distinction between cis and trans amides and, although the crystal structure for the control has the trans conformation, temperature-dependent NMR studies provide clear evidence for trans/cis isomerisation in D6-DMSO. Polar solvents tend to stabilise the trans structure for the pyrene amide group, even for longer oligo-proline units. Circular dichroism shows that the proline spacer for PY-P8-PER exists mainly in the all-trans geometry in methanol. Preferential excitation of the pyrene chromophore is possible at wavelengths in the 320-350 nm range and, for the dyad, is followed by efficacious EET to the perylene emitter. The probability for intramolecular EET, obtained from analysis of steady-state spectroscopic data, is ca. 80-90% in solvents of disparate polarity. Comparison with the Förster critical distance suggests the terminals are ca. 18 Å apart. Time-resolved fluorescence spectroscopy, in conjunction with DFT calculations, indicates the dyad exists as a handful of conformers displaying a narrow range of EET rates. Optimisation of a distributive model allows accurate simulation of the EET dynamics in terms of reasonable structures based on isomerisation of certain amide groups.

Free base porphyrin-cyanine dye conjugate: synthesis and optical properties

The covalent combination of a cyanine dye (IR-783) with a tetraphenyl porphyrin unit through an ether linkage results in a photoactive system capable of producing singlet oxygen. The synthesis, characterization and photophysical properties of the resulting novel free base porphyrin-cyanine conjugate named TPPO-IR-783 (TOI) is reported. Excited state properties were studied in various solvents with differing polarity. The fluorescence is strongly solvent dependent, however this is not the case for singlet oxygen phosphorescence, which is only observed in tetrahydrofuran (THF), when comparing 8 different polar, non-polar and medium-polarity solvents. This novel type of porphyrin-cyanine photosensitizer has the ability to produce singlet oxygen and absorbs light at NIR wavelengths.

Theoretical study on porphyrin arch-tapes of carbonyl-inserted seven-membered rings with high nonlinear optical properties

Porphyrin tapes have attracted extensive attention because their fully conjugated π-networks act as nonlinear optical (NLO) materials. A family of Ni(II) and Zn(II) porphyrin arch-tapes that are connected by varying bridge (B) ligands (meso-meso β-β doubly linked dimer 1, meso-meso β-β β-β triply linked dimer 3, methylene-inserted dimer 2 and trimer 5, carbonyl-inserted dimer 4, trimer 6, and Zn(II) trimer 7) have been synthesized by a density functional theory (DFT) method. The results show that carbonyl-inserted arch-tapes significantly enhance second hyperpolarizability (γ), indicating that the remarkably contorted structure incorporated seven-membered ring(s) directly affect their NLO properties of our focus. Moreover, the electronic absorption spectra calculated for all studied complexes with time-dependent DFT theory (TDDFT) predict that carbonyl-inserted complex 4 contributes to a red-shift of the Q-band (160 nm) for the meso-meso β-β doubly linked complex 1. The third-order NLO responses and the electron transition properties strongly depend on the nature of the bridge (B) ligand, which means that an active involvement of the carbonyl group presents an advantage for its application in NLO materials.

Panchromatic and Perturbed Absorption Spectral Features and Multiredox Properties of Dicyanovinyl- and Dicyanobutadienyl-Appended Cobalt Corroles

Four new β-functionalized π-extended cobalt corroles with one and two dicyanovinyl (DCV) or dicyanobutadienyl (DCBD) moieties at the 3- and 3,17-positions have been synthesized and characterized by various spectroscopic techniques. Interestingly, the synthesized DCV- and DCBD-appended cobalt corroles displayed panchromatic and near-infrared absorption in the range 300-1100 nm in CH2Cl2 and pyridine solvents. (MN)2-(Cor)Co and A2MN2-(Cor)Co exhibited 8-9 times enhancement in the molar absorptivity of the Q band compared to the parent corrole ((Cor)Co). The unique absorption spectral features of these β-functionalized cobalt corroles are splitting, broadening, and red-shifting in the Soret and Q bands. One DCV unit brings a 30-46 nm red shift, whereas one DCBD unit brings a 40-75 nm red shift in the Q band compared to the corresponding precursors. This is rare that the intensity of the longest Q band is greater than or equal to the Soret-like bands. These corrole derivatives exhibit UV-vis spectral features similar to those of chlorophyll a. A 220 mV positive shift per DCV group and 160 mV positive shift per DCBD group were observed in the first oxidation potentials compared to (Cor)Co in the desired direction for the utility of these cobalt complexes in electrocatalysis. DFT studies revealed that HOMO and LUMO were stabilized after appending DCV and DCBD groups on the corrole macrocycle and exhibited a "push-pull" behavior leading to promising material applications in nonlinear optics (NLO) and catalysis.

Synthesis and Characterization of Quinone Compounds Derived from Doubly and Triply Linked Diporphyrins and Tuning of Their Absorption Properties

Porphyrins are attracting increasing attention in materials science and photochemistry owing to their unique properties and diverse applications. This study focuses on modifying and tuning the absorption properties of porphyrins, specifically those of quinoidal porphyrins, to extend their spectral range into the near-infrared (NIR) region. We report the synthesis and structural and physical properties of quinone compounds derived from doubly and triply linked diporphyrins and their metal complexes. Doubly linked diporphyrinquinone exhibits broad panchromatic absorption properties in solution owing to its low symmetry. Metal complexation markedly extends its absorption range into the near-infrared region. In contrast, the metal complexes of the triply linked diporphyrinquinones exhibit sharp and strong absorption bands in the visible to near-infrared region owing to their higher symmetry. The longest absorption wavelength of the triply linked diporphyrinquinones was approximately 1500 nm, which was significantly more red-shifted than that of the doubly linked ones.

A Polymer-Derived Co(Fe)Ox Oxygen Evolution Catalyst Benefiting from the Oxidative Dehydrogenative Coupling of Cobalt Porphyrins

Thin films of cobalt porphyrin conjugated polymers bearing different substituents are prepared by oxidative chemical vapor deposition (oCVD) and investigated as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Interestingly, the electrocatalytic activity originates from polymer-derived, highly transparent Co(Fe)Ox species formed under operational alkaline conditions. Structural, compositional, electrical, and electrochemical characterizations reveal that the newly formed active catalyst greatly benefited from both the polymeric conformation of the porphyrin-based thin film and the inclusion of the iron-based species originating from the oCVD reaction. High-resolution mass spectrometry analyses combined with density functional theory (DFT) calculations showed that a close relationship exists between the porphyrin substituent, the extension of the π-conjugated system cobalt porphyrin conjugated polymer, and the dynamics of the polymer conversion leading to catalytically active Co(Fe)Ox species. This work evidences the precatalytic role of cobalt porphyrin conjugated polymers and uncovers the benefit of extended π-conjugation of the molecular matrix and iron inclusion on the formation and performance of the true active catalyst.

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 β-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.

Metallosupramolecular polymers: current status and future prospects

Metallo-supramolecular polymers have gained increasing attention and witnessed continuous development as a vibrant new research interest in the domain of soft materials. These nonconventional polymers have found widespread application in materials and biology owing to their well-defined and diversified topologies and the distinct dynamic nature of the metallosupramolecular interactions against various stimuli. Because of the intriguing redox, photonic, electronic, and magnetic properties, these stimuli-responsive supramolecular structures have attracted considerable interest for optoelectronic device fabrication. However, it still remains challenging to develop stimuli responsive systems with offbeat applications. Furthermore, achieving spatiotemporal control remains elusive with thermoresponsive and sono-responsive metallosupramolecular polymers, which encounter the disadvantage of poor precision control. Additionally, controlling the morphology of these soft materials on the mesoscale, both in solution and on substrates, has many challenges. In this review, we discuss the recent developments and future directions for the construction of stimuli responsive metallosupramolecular systems targeting practical applications. Furthermore, we discuss the synthetic methodologies that have been used to regulate the mesoscale morphology of these materials, such as coordination modulation and pseudomorphic replication. Finally, we briefly cover the burgeoning field of programmed synthesis of metallosupramolecular polymers, emphasizing techniques, such as living polymerization and chemical fuel-driven transiently active systems, which we believe will be the major research directions in the future.

Unleashing the power of porphyrin photosensitizers: Illuminating breakthroughs in photodynamic therapy

This comprehensive review provides the current trends and recent developments of porphyrin-based photosensitizers. We discuss their evolution from first-generation to third-generation compounds, including cutting-edge nanoparticle-integrated derivatives, and explores their pivotal role in advancing photodynamic therapy (PDT) for enhanced cancer treatment. Integrating porphyrins with nanoparticles represents a promising avenue, offering improved selectivity, reduced toxicity, and heightened biocompatibility. By elucidating recent breakthroughs, innovative methodologies, and emerging applications, this review provides a panoramic snapshot of the dynamic field, addressing challenges and charting prospects. With a focus on harnessing reactive oxygen species (ROS) through light activation, PDT serves as a minimally invasive therapeutic approach. This article offers a valuable resource for researchers, clinicians, and PDT enthusiasts, highlighting the potential of porphyrin photosensitizers to improve the future of cancer therapy.

Post-Installation of Fused Benzoheptagons at the Periphery of NiII Porphyrins: Helical Structures and Conformation-Adjustable Fullerenes Binding

Fused-benzoheptagon-installed NiII porphyrins were synthesized by a protocol consisting of (2-formyl)arylation at the meso-position(s) of NiII porphyrins, conversion of formyl group to methoxyethene group by Wittig reaction, and final Bi(OTf)3 -catalyzed cyclization. The structures of these porphyrins have been revealed by X-ray analysis. Owing to the installed heptagon ring(s), these porphyrins show curved structures with conformational flexibility. Dimer has been shown to have a small activation barrier for inversion and to capture C60 and C70 with large association constants with adjustable conformational changes.

Geometry-Independent Ultrafast Energy Transfer in Bioinspired Arrays Containing Electronically Coupled BODIPY Dimers as Energy Donors

In photosynthetic light-harvesting complexes, strong interaction between chromophores enables efficient absorption of solar radiation and has been suggested to enable ultrafast energy funneling to the reaction center. To examine whether similar effects can be realized in synthetic systems, and to determine the mechanisms of energy transfer, we synthesized and characterized a series of bioinspired arrays containing strongly-coupled BODIPY dimers as energy donors and chlorin derivatives as energy acceptors. The BODIPY dimers feature broad absorption in the range of 500-600 nm, complementing the chlorin absorption to provide absorption across the entire visible spectrum. Ultrafast (~10 ps) energy transfer was observed from photoexcited BODIPY dyads to chlorin subunits. Surprisingly, the energy-transfer rate is nearly independent of the position where the BODIPY dimer is attached to the chlorin and of the type of connecting linker. In addition, the energy-transfer rate from BODIPY dimers to chlorin is slower than the corresponding rate in arrays containing BODIPY monomers. The lower rate, corresponding to less efficient through-bond transfer, is most likely due to weaker electronic coupling between the ground state of the chlorin acceptor and the delocalized electronic state of the BODIPY dimer, compared to the localized state of a BODIPY monomer.