Free-base Porphyrin Research Articles

Orthogonal and antenna effects on the chemosensing behaviour of porphyrins towards 2,4,6-trinitrophenol: Colour recognition and portable photodiode device

In this work, we have developed two modular freebase porphyrins containing triphenylamine (H2TPAP) and pyrene (H2PyP) units at meso position to understand the role of antenna and orthogonal effects on photophysical and chemosensing behaviour with different nitroaromatic compounds (NACs). The fluorescence studies demonstrate that H2TPAP exhibit strong electronic coupling over H2PyP to induce energy transfer process from peripheral units to porphyrin π-system and behave like strong donor materials. The sequential energy and electron transfer process upon addition of different NACs reveals that H2TPAP show unprecedented selectivity towards the detection of 2,4,6-Trinitrophenol (TNP) with a limit of detection (LODs) of ∼2.3 and ∼6.8 ppm for H2PyP. The mechanistic investigations through NMR and other spectroscopic methods evident that the strong donor-acceptor interactions, protonation at the central core of H2TPAP show both colorimetric and fluorimetric changes with the order of quenching efficiency as TNP>4-NP>2,4-DNP > DUN>4-NBA. A handheld portable photodetector was developed to monitor the dynamic change in photocurrent response. Further, a smartphone interfaced portable fluorimetric method was developed by recognizing colour variations in terms of RGB and the luminance (L) values facilitate sensitive and real-time sensing at low concentrations levels will have a significant impact on the development of new handheld chemosensor devices for real time detection of explosive compounds.

Singlet oxygen generation by nanoassemblies containing porphyrin macrocycles: Steric and screening effects, energy transfer and competing processes

In this semi-review paper, we discuss some principal aspects that should be taken into account upon quantitative analysis of the interaction with molecular oxygen O2 and the singlet oxygen (1O2 or [Formula: see text] generation by various tetrapyrrolic photosensitizers (including monomers, chemical dimers, triads, pentads and organic-inorganic nanoassemblies). In all cases, the direct experimental measurements of 1O2 emission at [Formula: see text] = 1.27 μ need to be corrected to the solvent influence (refractive indexes, molecular polarizability) on the rate constant of the radiative transition [Formula: see text] in a 1O2 molecule. For porphyrin and chlorin chemical dimers, T1 states quenching by O2 followed by 1O2 generation depends on donor-acceptor interactions between the dimer halves, and extra-ligation effects as well as the spacer flexibility. In the case of self-assembled triads and pentads containing Zn-porphyrin dimers and pyridyl substituted porphyrin free bases (H2P) as extra-ligands, quenching rate constants of H2P T1 states by O2 are smaller compared to those found for individual monomeric H2P molecules which is explained by the spatial screening influence of a strongly quenched Zn-porphyrin dimer in multiporphyrin complexes. Finally, at 293 K for nanoassemblies of two types (semiconductor quantum dots CdSe/ZnS + coordinative linked tetra-pyridyl porphyrins, and semiconductor negatively charged quantum dots AgInS/ZnS + positively charged porphyrin molecules) it was quantitatively shown that non-radiative energy transfer FRET quantum dot [Formula: see text] porphyrin (competing with electron tunneling under conditions of quantum confinement) is only responsible for the singlet oxygen 1O2 generation by nanoassemblies.

Rigid and Flexible Bis-Porphyrinic Tweezers: Efficient Molecular Recognition of Bidentate Bases

Increasing efforts are devoted to the synthesis of cofacial bis-porphyrinic tweezers able to complex various bidentate guests through axial coordination of the Zn(II) porphyrins by the two nitrogen atoms. Elaboration of rigid receptors appeared up to now as the ideal way to pre-organize a bis-porphyrinic cavity and increase the stability of the formed host/guest complexes. However, the choice of using rigid spacer to attach the two porphyrins together may cost a lot as far as solubility and stability are concerned. The synthetic pathways necessary to achieve the synthesis of rigid systems are frequently long and tedious. We report here the synthesis and studies of new flexible bis-porphyrinic tweezers bearing uridine as linkers and offering pre-organized cavities able to welcome bidentate guests with extremely high association constants.As part of our studies concerning complexation of bidentate Lewis bases by bis-porphyrinic tweezers, we have synthesized two new bis-porphyrins bearing a flexible nucleosidic linker. Both uridine and 2’-deoxyuridine spacers were chosen on account of some observations we made a few years ago on the unexpected blocked conformations adopted by a pentaporphyrin consisting of four Zn(II) porphyrins attached to a central free-base porphyrin by four nucleosidic linkers. Since we observed no such blocked conformations in other flexible pentaporphyrins, we thought this might be due to the nucleosidic nature of the linkers. We thus synthesized two dimers, which differ by the attachment positions of the two porphyrins.The ability of these two tweezers to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these dimers was monitored by UV-visible spectrophotometric titration in CH2Cl2. The binding constants between these two tweezers and DABCO were calculated from UV-visible spectroscopic data. These association constants are unexpectedly increased by more than one order of magnitude as compared to the association constants of the same bidentate ligand with a reference Zn(II) mono-porphyrin. This enhanced stability of the complexes may be ascribed to a pre-organization of the bis-porphyrinic tweezers forming a cavity, and provides convincing evidence that the bidentate base is inserted into the cavity of the dimers via host/guest interactions.We demonstrated that similar association constants can be obtained with flexible tweezers bearing uridine as linker and rigid tweezers. However, the stability of these flexible complexes isn’t as convincing as for our rigid tweezers bearing a tris-anthracenic spacer since the addition of an excess of DABCO destroys all the flexible complexes.Molecular modelling of one of the flexible tweezers and its 1/1 complex with DABCO is represented below, as well as our rigid tweezers bearing a tris-anthracenic spacer. Acknowledgements This work was supported by the CNRS and the French Ministry of Research.

Synthesis of porphyrin triads chelated with thallium(III) for studies of ground-state hole/electron transfer

Four target all-porphyrin triads have been prepared for fundamental studies of ground-state hole/electron transfer. Each triad contains thallium(III) porphyrins as bookends, which bear mesityl groups at the three non-linking meso-positions. The central porphyrin is a free base or thallium(III) porphyrin bearing mesityl or pentafluorophenyl groups at the two non-linking meso-positions. The linker is a 4,4′-diphenylethyne unit joined at the porphyrin meso-positions. The net spacer between the two bookend thallium(III) porphyrins thus consists of diphenylethyne–porphyrin–diphenylethyne and is designed as a superexchange element for through-bond hole/electron transfer. The energetics of the superexchange element are tunable given the nature of the substituents and metalation state of the central porphyrin. The synthesis entailed Sonogashira coupling of two building blocks, a free base bis(4-iodophenyl)porphyrin and a mono-ethynylporphinato thallium(III) chloride. Two benchmark porphyrins also were prepared. Absorption spectral comparisons are provided including of the all-thallium(III) monomer, dimer, and triad.

Click approach for the synthesis of 1,4-disubstituted-1,2, 3-triazoles of porphyrin-isatin/sulfa drug conjugates based on m-THPP

New porphyrin-isatin/sulfa drugs conjugates based on symmetrical 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin ([Formula: see text]-THPP) with 1,4-regioisomers of 1,2,3-triazole linker were successfully synthesized. The constructed porphyrin-conjugates 15-19 and 22-24 contained mono-, tri- (unsymmetrical), or tetrafunctionalized units of isatin, sulfanilamide and sulfapyridine with 1,2,3-triazole linker. The synthesis of these conjugates was achieved by nucleophilic functionalization of [Formula: see text]-THPP by propargyl bromide followed by zinc metalation to achieve the mono-/tri-/tetrafunctionalized propargyl[Formula: see text]-THPP zinc-complex derivatives 3-5 (alkyne partners). The formed alkyne partners underwent cycloaddition reaction with isatin azide 8, azidosulfanilamide 13 and azidosulfapyridine 14 (azide partners) using click conditions via applying copper (I) catalyzed azide-alkyne cycloaddition (CuAAC). The utilized protocol succeeded in generating amphiphilic conjugates based on [Formula: see text]-THPP in an easy, simple, and quick manner, with high regioselectivity and high yields for potential medicinal and biological applications. The Zn-porphyrin derivatives’ photonic properties were investigated via photoabsorption and fluorescence. The optical properties were also studied and it is obvious that the Zn-porphyrin complex derivatives are different from those of the free-base porphyrin and could be relied on the number of triazole units and bioconjugate type.

Investigation of the free-base Zr-porphyrin MOFs as relative humidity sensors for an indoor setting

Maintaining optimal relative humidity is paramount for human comfort. Therefore, the utilization of quartz crystal microbalance (QCM) as a relative humidity sensor platform holds significant promise due to its cost-effectiveness and high sensitivity. This study explores the efficacy of three free-base Zr porphyrin metal-organic frameworks (MOFs) - namely MOF-525, MOF-545, and NU-902 - as sensitive materials for QCM-based relative humidity sensors. Our extended experimental findings reveal that these materials exhibit notable sensitivity, particularly within relative humidity ranges of 40–100 %. However, we observe potential irreversible adsorption sites within the MOF-545 framework, hindering its ability to revert to its initial state after prolonged exposure. In light of this observation, we conduct periodic cycling experiments at relative humidity levels of 40–70 % to evaluate the measurement repeatability and feasibility of these sensors for indoor applications. Interestingly, the periodic cycling study demonstrates that MOF-545 shows promising repeatability, positioning it as a strong contender for indoor relative humidity sensing. In contrast, MOF-525 may necessitate extended desorption time, and NU-902 displays diminished sensitivity at low relative humidity levels. Nevertheless, a preliminary treatment of the MOF-545 QCM sensor may be necessary to address irreversible adsorption sites and uphold measurement repeatability, as only reversible adsorption sites are currently accessible. This study underscores the potential of MOF-based QCM sensors for effective relative humidity monitoring in indoor environments, thus facilitating improved comfort and environmental control.

Optical properties of meso-tetra(sulphonatophenyl) porphyrins (TPPS 4) and their Fe 3+, Mn 3+, Zn 2+ complexes with different pH values studied using by picosecond pulse trains

Applying picosecond pulse trains propagating in meso-tetra(sulphonatophenyl) porphyrins and their Fe 3+, Mn 3+, Zn 2+ complexes, we studied the nonlinear dynamics at different pH values. The pulse train at wavelength 532nm is comprised of 20 subpulses with 70ps width and 13ns spacing. We simplified the energy structures of porphyrins and metalloporphyrins to five-level models. In solving coupled rate equations and two-dimensional paraxial field, we used Crank-Nicholson numerical method to do the calculations. The results revealed that in irregular metalloporphyrins with central paramagnetic ion Mn 3+ or Fe 3+, the central ion would act as electron acceptor, which leads to charge transfer of unpaired metal electron to the porphyrin ring π conjugated system, and strengthen the spin–orbit coupling of electronic systems and weaken the transition prohibition between electronic states in porphyrins. However regular metalloporphyrins with central diamagnetic ion Zn 2+ has similar optical properties to free base porphyrins, and Zn 2+ TPPS 4 has much longer excited state lifetimes and slower intersystem crossing. In solutions, hydrogen bond would be formed to porphyrin, which can change the transitions of π electrons and thus the charge transfer can be strengthened in the porphyrin ring. In weak intensity region with linear absorption, nonprotonated porphyrins with high pH value show better optical limiting (OL) effect. Conversely in high intensity region, protonated porphyrins with low pH value show better OL effect. Besides, increasing interaction distances of porphyrins and metalloporphyrins with laser pulses is another important factor to raise the OL effects.

Unraveling the role of non-planarity of free base porphyrins in intermolecular hydrogen bonding interactions with phenols

Three different types of meso‑substituted freebase porphyrins (H2TTP, H2TMP and H2DDMP) with varied number and nature of electron donating groups (-CH3 and –OCH3) were synthesized. The molecular interactions of the porphyrins with different phenol derivative were explored using single crystal X-ray, NMR and their affinity by varied spectroscopic techniques. All three freebase porphyrins undergo strong intermolecular interactions with 2,4,6-trinitrophenol (TNP) and crystallized in a triclinic crystal system with iso-structural behaviour. The crystal lattices are stabilized through intermolecular hydrogen bonding interactions (N–H∙∙∙O and C–H∙∙∙O) and electrostatic interactions. Increases in the non-planarity of freebase porphyrins enhance the reactivity which results in the formation of picrate anions with 1:2 adduct formation by proton transfer process. The role of weak intermolecular interactions was analysed and quantified through Hirshfeld surface and finger print analysis. DFT studies revealed that the electron-donating effect of the methoxy group plays a major role in decreasing HOMO-LUMO gap and in-plane co-operation through the decrease in the dihedral angles. The electron density at bond critical points follows the order H2TTP.2TNP>H2TMP.2TNP>H2DDMP.2TNP. Absorption and emission studies showed that dramatic changes in the Soret and Q-band pattern and the binding constants were altered with different phenols of varied pKa. The stabilization of molecular adducts were analyzed in correlation with 1H- NMR study to reveal the involvement of the hydrogen bonding.

Investigation of antimicrobial potential of nanocomposites based on functionalization of graphene oxide with zinc porphyrin complexes

Herein, zinc porphyrin complexes were synthesised by passing through the formation of free base porphyrin ligands and metalation of free base porphyrins with zinc metal ions. The synthesised zinc porphyrin complexes were functionalised with graphene oxide leading to the formation of zinc porphyrin anchored graphene oxide hybrid nanocomposites. The zinc porphyrins complexes were anchored with graphene oxide through the particular functional group present at the periphery of zinc porphyrins (hydroxyl and carboxyl functional groups in Pr1 and Pr2 respectively). 1H NMR and UV–visible spectroscopic techniques have monitored the successful formation of free base porphyrins and their matching zinc-integrated metalloporphyrin complexes. Various spectroscopic techniques like, photophysical properties (UV–Visible spectroscopy and Fluorescence spectroscopy), Fourier transform infrared (FT-IR), powdered X-ray diffraction (P-XRD) patterns, FE-SEM and EDAX analysis were used to examine the intrinsic characteristics of the prepared nanocomposites. The in-vitro antimicrobial activity of the synthesized complexes and nanocomposites was tested against Staphylococcus aureus gram-positive strain, Klebsiella pneumonia, and Escherichia coli. By working on the antimicrobial behaviour, it has been observed that the compound containing –COOH substitute has shown enhanced antimicrobial activity. The in silico molecular docking studies of the synthesized compounds with the S. aureus nucleoside diphosphate kinase receptor showed strong interactions via hydrogen bonding, π − π interactions and hydrophobic interactions. Molecular dynamics (MDs) simulations were used to study the dynamic behaviour of the complexes as well as nanocomposites which revealed the stability of docked structures with S. aureus nucleoside diphosphate kinase receptor. The in-silico pharmacokinetics studies showed the drug-likeness, non-toxic nature and safe oral administration of the synthesized compounds.

Implementation of bridged copolymerisation to optimise the optical properties of porphyrin: applications in dye-sensitized solar cells

This study explores the concept of all-organic sensitisation of dye-sensitized solar cells (DSSCs) by using a cosensitization approach to model efficient porphyrin-based photosensitizers. The aim is to enhance the absorption defects and light response current of porphyrin dyes, which have been reported in the literature. In this work, eight (8) natural porphyrin derivatives obtained through bridged copolymerisation of free base porphyrin and tetraazaporphyrin have been modelized and analysed. Their geometric parameters, stability energies, chemical stabilities, and photochemical properties were studied using density functional theory (DFT) methods in both gaseous and dichloromethane (DCM) phases. The analysis of photochemical properties, including maximum absorption wavelength ( λ max ), light harvesting efficiency (LHE), electron injection driving force ( Δ G inj ), regeneration driving force ( Δ G reg ), and excited state lifetime ( τ ) of the studied photosensitizers, show significant improvement compared to the parent dye (free base porphyrin) and some recent derivatives SM315 and YD2-o-C8. It is worth noting that the eight ( 8 ) modelled dyes from porphyrin show broader LHE curves not only compared to the parent dye, but also compared to the SM315 dye, which may lead to a higher running photo density. This study highlights the effectiveness of bridged copolymerisation for developing high-performance DSSCS based on porphyrin.

Customizable Porphyrin Platform Enables Folate Receptor PET Imaging Using Copper-64.

Folate receptors including folate receptor α (FRα) are overexpressed in up to 90% of ovarian cancers. Ovarian cancers overexpressing FRα often exhibit high degrees of drug resistance and poor outcomes. A porphyrin chassis has been developed that is readily customizable according to the desired targeting properties. Thus, compound O5 includes a free base porphyrin, two water-solubilizing groups that project above and below the macrocycle plane, and a folate targeting moiety. Compound O5 was synthesized (>95% purity) and exhibited aqueous solubility of at least 0.48 mM (1 mg/mL). Radiolabeling of O5 with 64Cu in HEPES buffer at 37 °C gave a molar activity of 1000 μCi/μg (88 MBq/nmol). [64Cu]Cu-O5 was stable in human serum for 24 h. Cell uptake studies showed 535 ± 12% bound/mg [64Cu]Cu-O5 in FRα-positive IGROV1 cells when incubated at 0.04 nM. Subcellular fractionation showed that most radioactivity was associated with the cytoplasmic (39.4 ± 2.7%) and chromatin-bound nuclear (53.0 ± 4.2%) fractions. In mice bearing IGROV1 xenografts, PET imaging studies showed clear tumor uptake of [64Cu]Cu-O5 from 1 to 24 h post injection with a low degree of liver uptake. The tumor standardized uptake value at 24 h post injection was 0.34 ± 0.16 versus 0.06 ± 0.07 in the blocking group. In summary, [64Cu]Cu-O5 was synthesized at high molar activity, was stable in serum, exhibited high binding to FRα-overexpressing cells with high nuclear translocation, and gave uptake that was clearly visible in mouse tumor xenografts.

Electroreduction mechanisms of meso-Tetraphenylphlorin cation in strongly acidic media of benzonitrile

In nonaqueous media free-base porphyrins are easily protonated by strong proton donors to form the diprotonated porphyrins. The two-electron reduction of these species leads to phlorin cation species. To investigate the electroreduction products that follow the formation of these species, we evaluate the effect of increasing amounts of HClO4 on the electroreduction mechanism of the phlorin cation of meso-tetraphenyl porphyrin. We demonstrate that the phlorin cation undergoes a reversible protonation reaction to form a porphodimethene, which is further reduced to yield the chlorin-phlorin cation, a 4-electron reduced phlorin macrocycle with a hydrogenated pyrrolic Cβ = Cβ double bond. This undergoes further protonation and a 2-electron reduction to form a phlorin macrocycle, the bacteriochlorin-phlorin cation, wherein two pyrrole rings are hydrogenated. All these reduction processes occur at similar potential values, yet we managed to selectively form the 2-, 4- or 6- electron reduced product by a strict control of the number of protons in the medium. To the best of our knowledge, this is the first report of the electrochemical reduction of Cβ = Cβ bonds of pyrrolic rings. Thus, a new pathway for the electrochemical reduction of porphyrins is proposed.

Cu-Metalated Porphyrin-Based MOFs Coupled with Anatase as Photocatalysts for CO2 Reduction: The Effect of Metalation Proportion

Converting carbon dioxide (CO2) into valuable chemicals such as fossil resources via photocatalysis requires the development of advanced materials. Herein, we coupled zirconium-based metal–organic frameworks (MOFs) containing porphyrin and Cu-porphyrin with anatase TiO2. The effect of the porphyrin metalation proportion was also investigated. Notably, while the use of free-base porphyrin as the organic linker resulted in the development of PCN-224, the presence of Cu-porphyrin provided mixed-phase MOF structures containing both PCN-224 and PCN-222. MOF/TiO2 composites bearing partial (50%) metalated porphyrin were proven more active and selective towards the production of CH4, at ambient conditions, in the gas phase and using water vapors without the use of hole scavengers. The optimized composite bearing 15 wt.% of the partial metalated MOF was three times more active than pure TiO2 towards CH4 production. This study provides insights on the effect of precise materials engineering at a molecular level on the development of advanced MOF-based photocatalysts for CO2 reduction.

Realization of either physisorption or chemisorption of 2H-tetraphenylporphyrin on the Cu(111) from density functional theory

The adsorption of organic molecules to surfaces is a central issue to achieve fully-functional molecular devices, for which porphyrins are well-studied due to their chemical stability and functional diversity. Herein, we investigate both the physical and the chemical adsorption of the free-base tetraphenylporphyrin 2H-TPP on the Cu(111) surface within the framework of density functional theory and find that the most stable physisorbed configuration is more weakly bound by −0.31 eV than the chemisorbed configuration. We use the electron localization function to investigate the difference in binding mechanisms between strong physisorption and weak chemisorption. We have computed a reaction barrier of 0.12 eV in going from physical binding to chemical bonding to the surface, and a barrier of 50 meV in going between neighboring physical binding sites. Our results support the possibility of realizing free-base porphyrins either physisorbed or chemisorbed on Cu(111) depending on the deposition procedure and experimental conditions.

Spectroscopic and quantum chemical insights on supramolecular interaction between N-methylfulleropyrrolidine and designed porphyrins in solution

Present letter describes self-assembly of N-methylfulleropyrrolidine (A) with a designed free-base (H2Pr) and zinc porphyrin (ZnPr) in toluene. The binding constants (K) of A-H2Pr and A-ZnPr systems are estimated to be 5.92 × 103 dm3.mol–1 and 10.05 × 103 dm3⋅mol−1, respectively. DFT calculations by B3LYP (and MO6) method(s) extend very good support in favour of the K values of the A-H2Pr and A-ZnPr systems in terms of the heat of formation, i.e., 7.40 kcal⋅mol−1 (and 6.46 kcal⋅mol−1) and −128.25 kcal⋅mol−1 (and −125.05 kcal⋅mol−1), respectively. Present investigations envisage that A may be suitably employed as fulleropyrrolidine based photochromic devices in near future.

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.

Identification by methods of steady-state and kinetic spectrofluorimetry of endogenous porphyrins and flavins sensitizing the formation of reactive oxygen species in cancer cells.

The question about acceptor molecules of optical radiation that determine the effects of photobiomodulation in relation to various types of cells still remains the focus of attention of researchers. This issue is most relevant for cancer cells, since, depending on the parameters of optical radiation, light can either stimulate their growth or inhibit them and lead to death. This study shows that endogenous porphyrins, which have sensitizing properties, may play an important role in the implementation of the effects of photobiomodulation, along with flavins. For the first time, using steady-state and kinetic spectrofluorimetry, free-base porphyrins and their zinc complexes were discovered and identified in living human cervical epithelial carcinoma (HeLa) cells, as well as in their extracts. It has been shown that reliable detection of porphyrin fluorescence in cells is hampered by the intense fluorescence of flavins due to their high concentration (micromolar range) and higher (compared to tetrapyrroles) fluorescence quantum yield. Optimization of the spectral range of excitation and the use of extractants that provide multiple quenching of the flavin component while increasing the emission efficiency of tetrapyrroles makes it possible to weaken the contribution of the flavin component to the recorded fluorescence spectra.

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.

Bioactive porphyrin magnesium (II) complex. Synthesis, molecular structure and spectroscopic characterization. Biological activity and molecular docking studies

We have synthesized and characterized porphyrin structures by UV–visible, IR and fluorescence spectroscopy studies and single crystal XRD analysis; H2(TPP) (I) (meso-tetraphenylporphyrin), [Mg(TPP)(DMF)] (II); (DMF: dimethylformamide) and [Mg(TPP)(H2O)]0.2(4-CNpy) (III); (4-CNpy: 4-Cyanopyridine). The crystal packing of the porphyrin structures is stabilized by intermolecular hydrogen bonds and by intermolecular CH⋯Cg π interactions where Cg is the centroid of the phenyl and pyrrole rings. UV–Vis spectroscopic data confirmed the creation of Mg-meso-porphyrin complexes by the red-shifted Soret bands for our derivatives compared to the free-base porphyrin. The optical gap energy values of (I), (II) and (III) are 1.92, 2.07 and 2.00 eV. Gram-positive and Gram-negative bacteria were tested against free porphyrin (I), metallated porphyrin (II) and complex (III). The results show that the magnesium porphyrin derivative is highly effective compared to H2TPP free-base porphyrins and metallated porphyrin [Mg(TPP)] and has higher inhibition character against the tested bacteria. The molecular docking of the complex (III), in the active sites of bacterial proteins was carried out to detect the degree of antibacterial activity of recognition.

Phosphonate-substituted porphyrins as efficient, cost-effective and reusable photocatalysts.

Recent advances in visible light photocatalysis represent a significant stride towards sustainable catalytic chemistry. However, its successful implementation in fine chemical production remains challenging and requires careful optimization of available photocatalysts. Our work aims to structurally modify bioinspired porphyrin catalysts, addressing issues related to their laborious synthesis and low solubility, with the goal of increasing their efficiency and developing reusable catalytic systems. We have demonstrated the catalytic potential of readily available meso-tetrakis[4-(diethoxyphosphoryl)phenyl]porphyrins (M(TPPP)). Novel metal (Pd(II), Co(II) and In(III)) complexes with this ligand were prepared in good yields. These chromophores were characterized in solution using spectroscopic (NMR, UV-vis, fluorescence) and electrochemical methods. The introduction of phosphonate groups on the phenyl substituents of meso-tetraphenylporphyrins (M(TPP)) improves solubility in polar organic solvents without significantly altering the photophysical properties and photostability of complexes. This structural modification also leads to easier reductions and harder oxidations of the macrocycle for all investigated complexes compared to the corresponding TPP derivatives. The free base porphyrin, zinc(II), palladium(II), and indium(III) complexes were studied as photocatalysts for oxidation of sulfides to sulfoxides using molecular oxygen as a terminal oxidant. Both dialkyl and alkyl aryl sulfides were quantitatively transformed into sulfoxides under blue LED irradiation in the acetonitrile-water mixture (10 : 1 v/v) with a low loading (0.005-0.05 mol%) of porphyrin photocatalysts, where H2(TPPP) and Pd(TPPP) were found to be the most efficient. The reaction mechanism was studied using photoluminescence and EPR spectroscopies. Then, to access reusable catalysts, water-soluble derivatives bearing phosphonic acid groups, H2(TPPP-A) and Pd(TPPP-A), were prepared in high yields. These compounds were characterized using spectroscopic methods. Single-crystal X-ray diffraction analysis of Pd(TPPP-A) reveals that the complex forms a 3D hydrogen-bonded organic framework (HOF) in the solid state. Both H2(TPPP-A) and Pd(TPPP-A) were found to catalyze the photooxidation of sulfides by molecular oxygen in the acetonitrile-water mixture (1 : 1 v/v), while only Pd(TPPP-A) resulted in selective production of sulfoxides. The complex Pd(TPPP-A) was easily recovered through extraction in the aqueous phase and successfully reused in five consecutive cycles of the sulfoxidation reaction.