Porphyrin Core Research Articles

Enhancing Targeted Photodynamic Therapy: Star-Shaped Glycopolymeric Photosensitizers for Improved Selectivity and Efficacy.

Targeted photodynamic therapy (PDT) offers advantages over nontargeted approaches, including improved selectivity, efficacy, and reduced side effects. This study developed star-shaped glycopolymeric photosensitizers using porphyrin-based initiators via ATRP. Incorporating a porphyrin core gave the polymers fluorescence and ROS generation, while adding fructose improved solubility and targeting capabilities. The photosensitizers had high light absorption, singlet oxygen production, specificity, low dark toxicity, and biocompatibility. The glycopolymers with longer sugar arms and higher density showed better uptake on MCF-7 and MDA-MB-468 cells compared to HeLa cells, indicating enhanced targeting capabilities. Inhibition of endocytosis confirmed the importance of the GLUT5 receptor. The resulting polymers exhibited good cytocompatibility under dark conditions and satisfactory PDT under light irradiation. Interestingly, the polymers containing fructose have a GLUT5-dependent elimination effect on the MCF-7 and MDA-MB-468 cells. The intracellular ROS production followed a similar pattern, indicating that the fructose polymer exhibits specific targeting toward cells with GLUT5 receptors.

Structural, photophysical, and electrochemical redox properties of meso-tetrakis(pentafluorophenyl)porphyrins

This study delineates the synthesis and comprehensive characterization of metal complexes of meso-tetrakis(pentafluorophenyl)porphyrin (H2TPF[Formula: see text]P, 1) with first-row transition metal ions (M = Mn(III) 2, Fe(III) 3, Co(II) 4, Ni(II) 5, Cu(II) 6, and Zn(II) 7) to elucidate their structural, electronic spectral, and electrochemical redox properties. Co, Ni, Cu and Zn Complexes exhibit planar structure ([Formula: see text]24 = 0.003-0.021 Å and [Formula: see text]C[Formula: see text] = 0.004−0.041 Å) which is also confirmed by the single crystal data of complex ZnTPF[Formula: see text]P, 7 shows the planar geometry, while Fe and Mn complexes show the slightly nonplanar structure ([Formula: see text]24 = 0.101–0.143 Å and [Formula: see text]C[Formula: see text] = 0.080–0.112 Å), which are distorted due to their occupied axial sites by −Cl ligand as revealed by density functional theory (DFT) calculations. Furthermore, electronic spectroscopy revealed a gradual bathochromic shift following the order of NiTPF[Formula: see text]P < CoTPF[Formula: see text]P < CuTPF[Formula: see text]PCl < H2TPF[Formula: see text]P = FeTPF[Formula: see text]PCl < ZnTPF[Formula: see text]P < MnTPF[Formula: see text]PCl by appending different metal ions in the porphyrin core. MnTPF[Formula: see text]PCl exhibited the most significant bathochromic shift ([Formula: see text] = 63 nm) in the Soret band compared to H2TPF[Formula: see text]P. Also, MnTPF[Formula: see text]PCl and FeTPF[Formula: see text]PCl show a unique pattern of split Soret band at around 364 and 345 nm due to the interaction between the metal [Formula: see text]-orbitals and the surrounding ligands. The electrochemical redox potentials of the filled 3d orbital of Zn endow ZnTPF[Formula: see text]P (ring centered) with the lowest oxidation potential.

Spectroscopic, X-ray structure, radical scavenging and in vitro antifungal activities and catalytic degradation of methyl orange dye investigation of the Meso-tetrakis(p-tolyl) diprotonated porphyrin

With the aim to fully characterize the diprotonated porphyrin: meso‑tetrakis(p-tolyl)porphyrindi-ium dichloride chloroform trisolvate with the formula [H4TTP]Cl2·3CHCl3 (2) this porphyrinic diacid species was first prepared by protonation of the meso‑tetrakis(p-tolyl)porphyrin (H2TTP, (1)). Compound 2 was studied by UV/Vis, fluorescence, IR, 1H NMR spectroscopy as well as by MALDI-TOF mass spectroscopy. The single crystal X-ray structure of 2 was a very useful technique to show the very important deformation of the porphyrin core of the diprotonated [H4TTP]2+ porphyrinic species (2) which is considered the principal cause of the important redshift of the UV/Vis and fluorescence spectra of compound 2. We used computational studies at B3LYP/6-311+G(d,p) level of theory to investigate the HOMO and LUMO molecular orbitals characteristics and calculate the global reactive parameters of compound 2 such as the electrophilicity index ψ, the chemical potential (μ), the hardness (η) and the chemical softness (S). The diacid porphyrin species (2) was tested as adsorbent of the Methyl Orange dye (MO) and also as catalyst of the degradation of this organic dye in presence of hydrogen peroxide. Biological studies on the H2TTP free base porphyrin (1) and the corresponding [H4TTP]2+ diacid species (2) were carried out in vitro in order to test their inhibitory effect against some fungal strings and the ability of these two porphyrinic compounds to scavenge 1,1-diphenyl-picrylhydrazyl DPPH radical.

Supramolecular chirality in self-assembly of zinc protobacteriochlorophyll-d analogs possessing enantiomeric esterifying groups

Zinc 3-hydroxymethyl-pyroprotopheophorbides-a esterified with a chiral secondary alcohol at the 17-propionate residue were prepared as bacteriochlorophyll-d analogs. The synthetic zinc 31-hydroxy-131-oxo-porphyrins self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted and broadened Soret and Qy absorption bands in comparison with their monomeric bands. The intense, exciton-coupled circular dichroism spectra of their self-aggregates were dependent on the chirality of the esterifying groups. The observation indicated that the self-aggregates based on the J-type stacking of the porphyrin cores were sensitive to the peripheral 17-propionate residues. The supramolecular structures of the present J-aggregates as models of bacteriochlorophyll aggregates in natural chlorosomes were remotely regulated by the esterifying groups.Graphical abstract

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy.

Photodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination-driven self-assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn-porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo-supramolecular PSs (S1-S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy

AbstractPhotodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination‐driven self‐assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn‐porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo‐supramolecular PSs (S1–S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Giant Star-shaped meso-substituted Fluorescent Porphyrins with Fluorenyl-containing Arms Designed for Two-photon Oxygen Photosensitization.

In the continuation of previous studies on carbon-rich meso-tetraarylporphyrins featuring 2,7-fluorene units at their periphery, the effect of changing the peripheral dendritic arms for linear arms on their oxygen-photosensitizing ability, their fluorescence and their two-photon absorption (2PA) properties is now analyzed. Thus, starburst porphyrins possessing up to twenty conjugated fluorenyl units were isolated and studied. More precisely, a series of five new free-base porphyrins featuring fully conjugated arms incorporating an increasing number of fluorenyl groups connected via 1,2-alkenyl spacers were synthesized, along with their Zn(II) complexes. Upon excitation in the arm-centred π-π* absorption band, an efficient energy transfer takes place from the peripheral fluorenyl units to the central porphyrin core, leading to intense red-light emission and oxygen photosensitization by the latter. More interestingly, while the linear optical properties of these porphyrins were only slightly improved compared to those of their dendrimer analogues for photodynamic therapy (PDT) or fluorescence imaging, their 2PA cross-sections were much more significantly boosted, evidencing the key role played by different structures on nonlinear optical properties. Finally, by comparison with other porphyrin-based two-photon photosensitizers reported in the literature, we show that these new "semi-disconnected" starburst systems exhibit a remarkable trade-off between intrinsic 2PA, fluorescence and oxygen photosensitization.

An ambipolar PEDOT-perfluorinated porphyrin electropolymer: application as an active material in energy storage systems.

The development of functional organic materials is crucial for the advancement of various fields, such as optoelectronics, energy storage, sensing, and biomedicine. In this context, we successfully prepared a stable ambipolar perfluoroporphyrin-based polymeric film by electrochemical synthesis. Our strategy involved the synthesis of a novel tetra-pentafluorophenyl porphyrin covalently linked to four 3,4-ethylenedioxythiophene (EDOT) moieties. The resulting monomer, EDOT-TPPF16, was obtained through a straightforward synthetic approach with a good overall yield. The unique molecular structure of EDOT-TPPF16 serves a dual function, with EDOT moieties allowing electropolymerization for polymeric film formation, while the electron-acceptor porphyrin core enables electrochemical reduction and electron transport. The electrochemical polymerization permits the polymer (PEDOT-TPPF16) synthesis and film formation in a reproducible and controllable manner in one step at room temperature. Spectroelectrochemical experiments confirmed that the porphyrin retained its optoelectronic properties within the polymeric matrix after the electrochemical polymerization. The obtained polymeric material exhibited stable redox capabilities. Current charge-discharge cycles and electrochemical impedance spectroscopy of the electrochemically generated organic film demonstrated that the polymer could be applied as a promising active material in the development of supercapacitor energy storage devices.

Porphyrins on acid: kinetics of the photoinduced-protonation of tetrakis(4-carboxyphenyl)-porphyrin.

Free-base porphyrins can be protonated, which significantly impacts their electronic and excited state properties. While excited state dynamics are well explored for either neutral or fully protonated porphyrins, the intermediate region has not yet been explored, although their potential implications for photocatalytic reactions are evident. This study explores how partial protonation affects the nature and properties of photoexcited states of tetrakis(4-carboxyphenyl)porphyrin (TCPP) using steady-state and nanosecond transient absorption spectroscopy. Global-fit analysis of the decay curves revealed the formation of a protonated excited triplet state from the neutral triplet state, as well as the long lifetimes of these species of up to 120 μs. The photoexcited triplet state of TCPP functions as a photobase, which was confirmed by computational analysis of the electron density of the exited states showing increased nucleophilicity at the unprotonated nitrogen atoms of the porphyrin core. These findings indicate that photoinduced protonated excited triplet states can function as electron acceptors with anodically shifted redox potentials, opening new pathways for porphyrin-based photoreactions.

VIS/NIR double-domain luminescence sensing with anti-interference performance by a lanthanide-organic framework nanosheet loaded with atomically dispersed Cu sites

Fluorescence/luminescence detection has garnered extensive attention due to its remarkable sensitivity and selectivity within the visible (VIS) and near-infrared (NIR) spectrum. However, detection in the VIS domain is susceptible to interference from background fluorescence and internal quenching effects; the reliability and stability of NIR detection are constrained by its luminescence efficiency and lifetime. In this context, we introduce a dual-domain detection strategy under both VIS and NIR illumination, leveraging the advantages of both domains to achieve anti-interference luminescence detection of tetracycline hydrochloride (TC). Specifically, Cu2+ ions were incorporated into Yb-TCPP nanosheets (H2TCPP = 5,10,15,20-tetra-(4-carboxyphenyl) porphyrin) and anchored at the porphyrin core of the TCPP2- ligand, forming highly dispersed Cu-N4 sites. Notably, the Cu@MOF luminescent material exhibited a picomolar level dual-domain fluorescence/luminescence response towards TC: it activates detection in the VIS domain and turns off in the NIR domain. Largely due to this dual-domain response, the sensor showcases excellent anti-interference capabilities and reliability. When the VIS domain is perturbed, the sensor's detection in the NIR domain remains unaffected; conversely, interference in the NIR domain barely impacts the sensor's behavior in the VIS domain. Furthermore, a systematic mechanistic analysis suggests that the introduction of atomically dispersed Cu2+ sites not only enhances the acid-base interaction sites between the sensor and the analyte but also amplifies the adsorption capacity towards the analyte, effectively reducing detection limits and bolstering anti-interference capabilities. Anticipating the future, this detection strategy holds promise in offering a more cost-effective, reliable, and interference-resistant option for commercial detection, signaling a bright prospect for its development.

Acenaphthenediimine complex-bridged porphyrin porous organic polymer with enriched active sites as a robust water splitting electrocatalyst

To realize efficient water splitting, a highly promising hydrogen evolution reaction (HER) electrocatalyst is needed for the generation of hydrogen. Herein, we demonstrate a novel acenaphthenediimine complex-bridged porphyrin porous organic polymer (NiTAPP-NiACQ) with enriched active metal sites and hierarchical pores. The as-prepared NiTAPP-NiACQ exhibits good long-term durability and remarkable HER performance in 1.0 M KOH with a low overpotential of 117 mV at 10 mA cm−2, which is comparable to many previously reported electrocatalytic HER systems. Furthermore, a simple water-alkali electrolyzer using NiTAPP-NiACQ as the cathode requires a small cell voltage of 1.59 V to deliver a current density of 10 mA cm−2 at room temperature, along with outstanding durability. NiTAPP-NiACQ features not only a metal ion as the catalytic active center in the porphyrin core but also metal ion coordination on the anthraquinone component to promote HER performance, enabling multiple metal ions as the electrocatalytic active sites for the HER reaction. The excellent HER activity of NiTAPP-NiACQ is ascribed to a combination of mechanisms. These findings highlight the viability of porphyrin-derived porous organic polymers in energy conversion processes.

A cancer cell and lysosome dual-targeted photosensitizer for fluorescence imaging and photodynamic therapy

A novel cancer cell and lysosome dual-targeted photosensitizer (PS) termed by BMP was developed for fluorescence imaging and photodynamic therapy (PDT). BMP consists of a porphyrin(Zn) core with appropriate singlet-triplet state distribution enables it to function as an imaging agent as well as a PS, a biotin moiety that can target cancer cells, and a morpholine group specific to lysosomes. Intracellular experiments demonstrated that the dual-targeted photosensitizer BMP could preferably accumulate in cancer cells and subsequently locate within lysosome organelles. Upon irradiation, BMP could generate red fluorescence emission (Φem = 6.3%) and singlet oxygen (1O2, ΦΔ = 55%) for the dual functionality of cell imaging and PDT, respectively. Notably, BMP exhibited much higher photocytotoxicity toward cancer cells (A549 cells) compared to normal cells (BEAS-2B cells). Importantly, 1O2 produced by BMP induced oxidative damage of lysosomes, and subsequently triggered cell death of A549 cells, as evidenced by the loss of morphological integrity and cell rupture.

Size‐ and charge‐matching effect between porphyrin core and central metal on the stability of cuprous ion

Cuprous(I) catalysts have been widely used in the coupling reaction of forming C‐X bond. The core‐modified porphyrins are known to stabilize the unusual oxidation state of many metals. Thus, in this work, a 21‐oxaporphyrin was obtained under the improved Adler–Longo condensation condition and successfully used for complexing the cuprous ion. It is found that the synergy of the two factors, the diameter expansion and the univalent form of the N₃O core in the ligand, plays a decisive role in stabilizing the metastable ion; the former effectively stabilizes the electron pair of the equatorial d orbital by aiding the d‐π interaction, and the latter exactly balances the single charge of the ion. A size axis of copper species in porphyrinate systems is established by comparing with two previously reported distorted copper(II) porphyrin series.

Synthesis, spectroscopic and electrochemical investigation on the conformational features of meso-5-formylthien-2-ylporphyrins and its terpyridinylthien-2-ylporphyrin and Porphyrin-Corrole dyad

A facile approach for the syntheses of regioselective meso- mono, di (cis and trans), and tri formylthien-2-ylporphyrins from meso-tetrathien-2-ylporphyrin (ThP) is presented. The synthesized meso- mono formylthien-2-ylporphyrin ThP-CHO was further functionalized to 5-((5-terpyridinyl)thien-2-yl)-10,15,20-tris(thien-2-yl)porphyrin (ThP-TPy) and Porphyrin-Corrole (Por-Cor) dyad. The influence of formyl substitution and further functionalization on meso- thien-2-yl ring(s) with porphyrin central π-system is examined through UV–Vis absorption, 1H NMR spectroscopy and electrochemical studies. The red shift of Soret band and Q bands in the absorption spectrum and the redox potentials are shown to be dependent on the number of substitution (ThP-CHO, 424 nm < ThPt-(CHO)2 and ThPc-(CHO)2, 425 nm < ThP(CHO)3, 427 nm). The significant variation in redox potentials and distinct bathochromic shift in the absorption bands in the series of formyl derivatives, ThP-TPy and Por-Cor dyad have been explained based on the near-planar orientation of the meso-thienyl groups with the porphyrin core.

The Influence of the Central Metal Ion on the Electronic and Photovoltaic Properties of Metalloporphyrins [M= Zn(II), Ni(II), Cu(II), Au(III)] Systems

Although the pioneering use of porphyrins in organic solar cells (OSCs) was disappointing as reported efficiencies were very low, the situation has changed over the last five years as Zn-porphyrins with ABAB structures linked to acceptor units through triple bonds have been applied as donors resulting in efficiencies of up to 12% in binary OSCs and more than 15% in ternary OSCs.The optical and electrochemical properties of porphyrins can be adjusted by molecular design and functionalization on the b or meso positions of the porphyrin ring as well as by introduction of different central metal ions. The choice of the centrally bounded metal cation within the porphyrin core plays an important role in the electronic properties allowing the modulation of the frontier orbital levels and thereby use the porphyrin-based molecule as donor or acceptor component of the device.Due to the high HOMO level of Zn-Porphyrin derivatives, the Voc of OSCs using this family of compounds are lower than 0.9 V limiting the PCE of devices.We have described that Ni-porphyrins derivatives allow the design of OSCs with voltage higher than 1V. These systems present slightly higher optical bandgaps but the deeper highest occupied molecular orbital (HOMO) energy level make available to reach good PCE values of the solar devices.While porphyrins and their derivatives have been extensively used as donor component in the BHJ active layer of OSCs, the investigation of porphyrin-based materials as electron acceptor is very limited. Recently, we designed a new A2-D-A1-D-A2 non fullerene small molecule acceptor (NFSMA) with broad absorption up to 920 nm and a great absorption coefficient where A1 core is Au(III) porphyrin. This molecule, when used in OSC with a polymer donor yielded a PCE=9.24%. Nevertheless, the use of other central metals such as Cu(II) in the porphyrin core has been scarcely used in OSCs, the studied devices presented low efficiencies (≤ 3%). These outcomes demonstrated that metalloporphyrins, which is different from Zn-porphyrins, also have great potential for the design of NFSMAs for efficient OSCs. Also, we have studied A-π-D-π-A small molecules based on Cu(II) Porphyrin, scarcely used in OSCs, presenting an ambipolar behaviour, as donor and as acceptor. Here, I´ll present our recent work in design, synthesis, and application of porphyrin-based small molecules with different central metal for highly efficient OSCs.References V. Cuesta, M. Vartanian, P. de la Cruz, R. Singhal, G. D. Sharma and F. Langa. J. Mater. Chem. A, 2017, 5, 1057.S. Arrechea, A. Aljarilla, P. de la Cruz, M. K. Singh, G. D. Sharma and F. Langa. J. Mater. Chem. C, 2017, 5, 4742.M. Vartanian, R. Singhal, P. de la Cruz, S. Biswas, G. D. Sharma and F. Langa. ACS Appl. Energy, Mater., 2018, 1, 1304.M. Vartanian, P. de la Cruz, F. Langa, S. Biswas and G. D. Sharma. Nanoscale, 2018, 10, 12100.M. Vartanian, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa. Chem. Commun., 2018, 54, 14144.V. Cuesta, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa. ACS Appl. Mater. Interfaces, 2019, 11, 7216.Cuesta, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa, ChemSusChem, 2021, 14, 3439.H. Dahiya, V. Cuesta, P. de la Cruz, F. Langa and G. D. Sharma ACS Appl. Energy Mater., 2021, 4, 4498. Figure 1

An electrochemical aptasensor for the detection of chloramphenicol based on ultra-small Au-inserted hollow PCN-222 MOF.

The excessive utilization of antibiotics has led to significant water contamination and posed severe threats to human well-being. Consequently, the pressing imperative to identify antibiotics in the environment arises. In this study, we have successfully synthesized a hollow PCN-222 MOF distinguished by its substantial surface area and abundant functional groups, particularly the porphyrin cores. To augment the electrical conductivity of the hollow PCN-222 (HPCN-222), gold (Au) particles were incorporated within the porphyrin core using a fundamental hydrothermal method. This modification facilitated the effective immobilization of aptamer strands through π-π stacking and electrostatic interactions. As a result, the Au@HPCN-222 composite demonstrated exceptional efficacy as a substrate for immobilizing the aptamer (Apt) onto the GCE surface. By employing differential pulse voltammetry (DPV) we successfully achieved the detection of chloramphenicol (CAP) with a remarkably low limit of detection of 0.0138ngmL-1 and the peak DPV currents at 0.18V (vs. Ag/AgCl) were used for calibration. Furthermore, this aptasensor exhibited high selectivity and reproducibility.

Mixed-Blocks-Driving Nickel-Porphyrin Covalent Organic Polymers for Photocatalytic Syngas Production from CO2 with Fine Selectivity.

CO2 photoconversion to syngas with superb selectivity is a splendid and bright option to achieve environmental improvement, energy substitution, and industrial needs. Herein, a series of Ni-porphyrin covalent organic polymers (COPs) interspersed with furan and thiophene using a mixed-blocks-engineering strategy, named as OXSY-Ni COPs (X and Y refer to the relative amounts of furan and thiophene blocks, respectively), are synthesized for photocatalytic CO2-to-syngas. Ni-coordinated porphyrin cores prefer to act as mediators of CO2-to-CO photoconversion because of the higher adsorption capacity of CO2. Ni-free porphyrins work mainly as active sites of H2 photoevolution. Furthermore, introducing different amounts of furan and thiophene modulates jointly the electronic structure of Ni-porphyrin COPs and optimizes the conduction band alignment. The above controllable variables achieve a wonderful syngas (CO/H2) ratio range from 2:1.06 to 1:1.04 for the Fischer-Tropsch process within common industrial reactions. Notably, the COP of the O1S3-Ni COPs exhibits excellent photocatalytic CO2-to-syngas activity under visible light, with a syngas yield of 8442.5 μmol g-1 h-1 (CO/H2 = 1:1.02) and an apparent quantum efficiency (AQE) of 1.92% at 450 nm. This strategy would provide a significance path to design functional and efficient organic semiconductors.

Distortion effect on the ligation of imidazoles to water-insoluble iron(III) porphyrin

Axial ligands control the various chemical reactions triggered by heme proteins. Thus, studies on the reaction of iron porphyrin with ligands are important for understanding their functions. Here, a spectroscopic investigation was performed to clarify the distortion effect of the porphyrin ring on the ligation of imidazoles (imidazole (Im), 1-methyl- and 2-methylimidazole (1-MeIm and 2-MeIm)) to iron(III) porphyrin. The overall stability constant ([Formula: see text] was found to have increased, while [Formula: see text] decreased with increasing distortion of the porphyrin core. However, the [Formula: see text] of the tetraphenyl-substituted complex, which is considered the least distorted, was not minimal, while the [Formula: see text] was not maximal. These results suggest that the stability of bis-ligand iron(III) porphyrin complexes depends on the increase in the saddle-type distortion of the porphyrin, the type of distortion, and the steric hindrance at the surrounding substituents. Furthermore, the ligation of 1-MeIm to iron(III) porphyrin hydroxo complexes with the porphyrin ring distortion was investigated. The ligation of 1-MeIm to the iron(III) dodecaphenylporphyrin hydroxo complex (DPPFeOH) suggests that a reaction mechanism different from the general reaction mechanism may occur simultaneously, i.e., a simultaneous reaction. In addition, the [Formula: see text] of DPPFeOH was found to be approximately 15 times smaller than that of the chloride complex. The relationship between the distortion and stability of bis-ligands iron(III) porphyrin complexes obtained in this study is expected to assist in the elucidation of the model reaction of heme proteins.

Photophysical properties of 5-(4-acetamidophenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin trichloride and its Zn(II) complex

The spectral and photophysical properties of two porphyrins, 5-(4-acetamidophenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin trichloride (1) and its Zn(II) complex 2 were investigated in different solvents by absorption, steady-state and time-resolved fluorescence spectroscopy, and laser flash photolysis. The findings were corroborated by computations at the TD-B3LYP/6-31++G(d,p) level of theory. The absorption spectra of 1 and 2 are the typical for porphyrins and their Zn complexes with the Soret bands at ≈ 420 nm and 430 nm, respectively, and the Q-bands at 515–650 nm, and 560–605 nm. Smaller differences in the absorption spectra compared to the symmetric porphyrins were assigned to more pronounced HOMO and HOMO-1 energy levels splitting in the asymmetric molecules. The temperature dependence of the absorption spectra with hypsochromic shifts suggests the formation of H-aggregates. The emission spectra are situated at 600–700 nm, and the vibronic resolution of the spectra for 1 depends on the solvent and the excitation wavelength, which was assigned due to the tautomerism by H-transfer within the porphyrin core. Quantum yields of fluorescence for 1 and 2 in methanolic solutions are Φf = 0.072 and 0.051, respectively. Although, the steady-state fluorescence spectra do not indicate that 1 and 2 form aggregates in methanolic and aqueous solutions (at <10-4 M), singlet decays measured by time-correlated single photon counting for both compounds were fit to multiexponential functions, which was explained by formation of aggregates in more concentrated solutions. Furthermore, at very high concentrations of 1 in CH3OH (>10-4 M), the dynamic formation of aggregates was evidenced by new bathochromically shifted band in the emission spectrum and the growth kinetics in the time-resolved fluorescence measurement. Triplet excited states of 1 and 2 were probed by laser flash photolysis. The triplets are populated with quantum yields of intersystem crossing, ΦISC = 0.34 and 0.41, respectively and lifetimes of the triplet excited states are in millisecond time-scale. Both triplets are quenched by O2 with the rate constants approaching diffusion limits. Relative quantum yields for the singlet oxygen formation are 0.86 and 0.92 respectively, rendering porphyrins 1 and 2 applicable for photodynamic therapy.

Design of AIEgen‐based porphyrin for efficient heterogeneous photocatalytic hydrogen evolution

AbstractTetraphenylethylene (TPE)‐conjugated porphyrin TPE‐ZnPF is synthesized in high yield and characterized by single‐crystal X‐ray diffraction. The propeller‐shaped TPE groups not only enable exceptional aggregation‐induced emission (AIE) in the solid state but also abolish the strong π‐π stacking of porphyrin moieties and thus prohibit aggregation‐caused quenching (ACQ). TPE‐ZnPF aggregates feature long‐lived photoexcited states, which subsequently suppress non‐radiative decay channels and enhance emission intensity. Moreover, its aggregates show more efficient light‐harvesting ability due to the Förster resonance energy transfer from the TPE energy donor to the porphyrin core energy acceptor, well‐defined nanosphere morphology, and more efficient photoinduced charge separation than the porphyrin Ph‐ZnPF, which possesses ACQ and agglomerated morphology. As a result, an excellent photocatalytic hydrogen evolution rate (ηH2) of 56.20 mmol g‒1 h‒1 is recorded for TPE‐ZnPF aggregates, which is 94‐fold higher than that of the aggregates of Ph‐ZnPF (0.60 mmol g‒1 h‒1) without the TPE groups.