Water-soluble ionic benzoporphyrins

Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation

Unsymmetric pentacenequinone-fused (cross-conjugated) and pentacene-fused (linear-conjugated) porphyrins were designed and synthesized. The cross-conjugated (AM ₁ -AM ₃ ) and linear-conjugated (AM ₅ -AM ₇ ) porphyrins displayed strikingly different sets of optical and electronic properties, both of which are unusual and nontypical of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple charge transfer states exist in both π-conjugated systems, which contributes to the complex absorption and MCD spectra of these molecular systems. The general Gouterman's four-orbital model used to explain porphyrin spectroscopy led to contradicting theoretical and experimental data, and is thus not applicable for these molecular systems. The "2 + 4" and "3 + 3" active spaces have been deduced and have proven effective to interpret the absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated) and pentacene-fused (linear-conjugated) porphyrins, respectively. Spectroelectrochemistry of AM ₅ -AM ₇ revealed broad and intense IR absorptions in the range of 1500-2500 nm, illustrating the exceptional ability of these pentacene-fused systems to accommodate positive charges. A pronounced metal effect was observed for pentacene-fused porphyrins. While pentacene-fused Ni(II) porphyrin (AM₆ ) demonstrated an abnormal ability to stabilize pentacene with a half-life of >28.3 days, the half-life of the free base and Zn(II) counterparts were normal, similar to those of pentacene analogues. This work provides important and useful information on guiding new material designs.

Porphyrindiene-Based Tandem Diels-Alder Reaction for Preparing Low-Symmetry π-Extended Porphyrins with Push-Pull Skeletons

Tandem Diels-Alder reactions of masked porphyrindienes (i.e., sulfolenoporphyrins) with benzoquinones and stilbenes, followed by aromatization, have been developed to load porphyrin with mixed annulation units (i.e., terphenyl and naphthoquinone), furnishing the low-symmetry π-extended porphyrins (DxAy) with push-pull skeletons. All low-symmetrical chromophores display panchromatic absorption spectra, which look like a spectral combination of symmetrical congeners (D4/A4) in a certain ratio. Among them, tD2A2 with trans-arrangement of push/pull units possesses the largest maximum centered at 766 nm with the onset around 900 nm. The fusion of the electron-deficient naphthoquinone moiety on the porphyrin core results in the approximately quantitative regulation of the E_ox1 and HOMOs (i.e., 0.10-0.13 V increase for the E_ox1 and 0.14-0.16 eV decrease for the HOMOs per naphthoquinone unit). In brief, this work provides a new way to construct low-symmetry π-extended porphyrins with tunable properties resorting to the ratios and locations of the annulated push-pull units.

Aromatic heterobicycle-fused porphyrins: impact on aromaticity and excited state electron transfer leading to long-lived charge separation

A new synthetic method to fuse benzo[4,5]imidazo[2,1-a]isoindole to the porphyrin periphery at the β,β-positions has been developed, and its impact on the aromaticity and electronic structures is investigated. Reactivity investigation of the fused benzoimidazo-isoindole component reveals fluorescence quenching of a zinc porphyrin (AMIm-2) upon treatment with a Brønsted acid. The reaction of the zinc porphyrin (AMIm-2) with methyl iodide initiated a new organic transformation, resulting in the ring-opening of isoindole with the formation of an aldehyde and dimethylation of the benzoimidazo component. The fused benzoimidazo-isoindole component acted as a good ligand to bind platinum(ii), forming novel homobimetallic and heterobimetallic porphyrin complexes. The fusion of benzoimidazo-isoindole on the porphyrin ring resulted in bathochromically shifted absorptions and emissions, reflecting the extended conjugation of the porphyrin π-system. Time-resolved emission and transient absorption spectroscopy revealed stable excited state species of the benzoimidazo-isoindole fused porphyrins. Zinc porphyrin AMIm-2 promoted excited state electron transfer upon coordinating with an electron acceptor, C₆₀, generating a long-lived charge-separated state, in the order of 37.4 μs. The formation of the exceptionally long-lived charge-separated state is attributed to the involvement of both singlet and triplet excited states of AMIm-2, which is rarely reported in porphyrins.

π-Extended porphyrins fused with benzo[4,5]imidazo[2,1-a]isoindole, showing unique electronic and photophysical properties, were newly synthesized. A long-lived charge-separated state was revealed upon coordination of C₆₀ to zinc porphyrin AMIm-2.

Graphene Oxide and Graphene Quantum Dots as Delivery Systems of Cationic Porphyrins: Photo-Antiproliferative Activity Evaluation towards T24 Human Bladder Cancer Cells

The development of new photodynamic therapy (PDT) agents designed for bladder cancer (BC) treatments is of utmost importance to prevent its recurrence and progression towards more invasive forms. Here, three different porphyrinic photosensitizers (PS) (TMPyP, Zn-TMPyP, and P1-C₅) were non-covalently loaded onto graphene oxide (GO) or graphene quantum dots (GQDs) in a one-step process. The cytotoxic effects of the free PS and of the corresponding hybrids were compared upon blue (BL) and red-light (RL) exposure on T24 human BC cells. In addition, intracellular reactive oxygen species (ROS) and singlet oxygen generation were measured. TMPyP and Zn-TMPyP showed higher efficiency under BL (IC₅₀: 0.42 and 0.22 μm, respectively), while P1-C₅ was more active under RL (IC₅₀: 0.14 μm). In general, these PS could induce apoptotic cell death through lysosomes damage. The in vitro photosensitizing activity of the PS was not compromised after their immobilization onto graphene-based nanomaterials, with Zn-TMPyP@GQDs being the most promising hybrid system under RL (IC₅₀: 0.37 μg/mL). Overall, our data confirm that GO and GQDs may represent valid platforms for PS delivery, without altering their performance for PDT on BC cells.

Bactericidal efficiency of porphyrin systems

Photodynamic Inactivation is an innovative technique used to combat bacterial and viral infections which involves the use of photosensitizing agents along with light to generate cytotoxic reactive oxygen species able to kill bacteria and viruses. In the first section of this minireview, porphyrin-based fluorophores are shown to be remarkable dye candidates for PDI (photodynamic inactivation) applications. The second section is dedicated to the description of porphyrin-based antimicrobial materials and their potentialities for industrial applications such as in food packaging or antimicrobial medical devices and hygiene. Finally, the failings and perspectives of PDI are analyzed to demonstrate how the PDI technique could be an efficient and ecologically friendly antimicrobial technique.

syn-Diarylphthalimidoporphyrins: Effects of Symmetry Breaking on Two-Photon Absorption and Linear Photophysical Properties

Aromatically π-extended porphyrins possess exceptionally intense one-photon (1P) and sometimes two-photon (2P) absorption bands, presenting interest for construction of optical imaging probes and photodynamic agents. Here we investigated how breaking the molecular symmetry affects linear and 2PA properties of π-extended porphyrins. First, we developed the synthesis of porphyrins fused with two phthalimide fragments, termed syn-diarylphthalimidoporphyrins (DAPIP). Second, the photophysical properties of H₂, Zn, Pd, and Pt DAPIP were measured and compared to those of fully symmetric tetraarylphthalimidoporphyrins (TAPIP). The data were interpreted using DFT/TDDFT calculations and sum-over-states (SOS) formalism. Overall, the picture of 2PA in DAPIP was found to resemble that in centrosymmetric porphyrins, indicating that symmetry breaking, even as significant as by syn-phthalimido-fusion, induces a relatively small perturbation to the porphyrin electronic structure. Collectively, the compact size, versatile synthesis, high 1PA and 2PA cross sections, and bright luminescence make DAPIP valuable chromophores for construction of imaging probes and other bioapplications.

Two- and three-dimensional β,β′-N-heterocycle fused porphyrins: concise construction, singlet oxygen production and electro-catalytic hydrogen evolution reaction

A series of 2D and 3D porphyrins fused with N-heterocycles were prepared by palladium-catalyzed. Photophysical and electrochemical properties, 1O2 production and electrocatalytic HER behaviours of the representative porphyrins were investigated.

Nickel(II) Bisporphyrin-Fused Pentacenes Exhibiting Abnormal High Stability

A series of largely π-extended multichromophoric molecules including cross-conjugated, half cross-conjugated, conjugation-interrupted and linearly conjugated systems were synthesized and characterized. These multichromophoric molecular systems revealed interesting structural-property relationships. Bisporphyrin-fused pentacenes Pen-1 b and Pen-2 a showed rich redox chemistry with 7 and 8 observable redox states, respectively. The linearly-conjugated bisporphyrin-fused pentacenes (Pen-1 b and Pen-2 a) possess much narrower HOMO-LUMO gaps (1.65 and 1.42 eV redox, respectively) and higher HOMO energy levels than those of their pentacene analogues (2.23 and 2.01 eV redox, respectively), similar to those of much less stable hexacenes and heptacenes. An estimated half-life of >945 h was obtained for bisporphyrin-fused pentacene Pen-2 a, which is much longer than that of its pentacene analogue (BPE-P, half-life, 33 h).

Synthesis of highly water soluble tetrabenzoporphyrins and their application toward photodynamic therapy

Novel tetraaryl-(pyridinium-4-yl)-tetrabenzoporphyrins have been successfully synthesized via a Heck-based sequence reaction. These tetrabenzoporphyrins were substituted with eight pyridyl groups at the fused benzene rings. Methylation of the pyridyl groups with methyl iodide afforded highly water soluble tetrabenzoporphyrins carrying eight ionic groups. The extended [Formula: see text]-conjugation broadened and red-shifted the absorption band of these porphyrins to 650–750 nm. These cationic tetrabenzoporphyrins showed non-toxicity in the dark up to 100 uM. High phototoxicity with IC[Formula: see text] values lower than 18 [Formula: see text]M were obtained for these tetrabenzoporphyrins.

Synthesis, singlet oxygen generation and DNA photocleavage of β,β′-conjugated polycationic porphyrins

In this paper, three [Formula: see text],[Formula: see text]-conjugated cationic porphyrin compounds were designed and synthesized. The structure of the intermediates and desired porphyrins were confirmed by UV, IR, 1H NMR, MS and elemental analysis. The interaction modes between these porphyrins and ct-DNA were studied by UV-vis spectroscopy and fluorescence emission spectroscopy. The results showed that PCP 1 had an external binding mode with DNA at low DNA concentration and could intercalate DNA with the increase of concentration. PCP 2 interacted with DNA through an external binding mode, and PCP 3 could insert into DNA. The binding constants ([Formula: see text] between PCP1[Formula: see text]PCP3 and ct-DNA were calculated to be 8.41 × 104, 7.33 × 104 and 4.14 × 104 M[Formula: see text], respectively. The singlet oxygen (1O[Formula: see text] generation of PCP1[Formula: see text]PCP3 was determined by the 1,3-diphenylisobenzofuran (DPBF) method using tetrapyridylporphyrin (H2TMPyP) as a reference. The 1O2 generation rate of PCP1[Formula: see text]PCP3 followed the order of PCP2 >PCP1>H2TMPyP >PCP3. Subsequently, the photocleavage effect of porphyrins on pBR322 plasmid DNA was studied by gel electrophoresis. At 10.0 [Formula: see text]M, PCP1 and PCP2 could cleave DNA completely. At 2.0 [Formula: see text]M, the cleavage rate of DNA by PCP3 was 57.5%, which was significantly higher than that of H2TMPyP (38.8%). These results verified that the amount of cationic ions in the porphyrin structure could affect the binding modes of porphyrins with DNA and their cleavage ability of DNA.

Tetrakis(ethyl-4(4-butyryl)oxyphenyl)porphyrinato zinc complexes with 4,4'-bpyridin: synthesis, characterization, and its catalytic degradation of Calmagite

This work reports on the synthesis and characterization of a new porphyrins complex:[Zn(TEBOP)(4,4'-bpy)](4,4'-bipyridine)(5,10,15,20-(tetraethyl-4(4-butyryl)oxyphenyl)porphyrinato)zinc(ii) (3). Single crystal X-ray diffraction, photophysical and electrochemical characteristics were studied. The prepared complex, penta-coordinated zinc(ii) porphyrin derivatives shows moderate ruffling distortion and the zinc atom is nearly planar with the porphyrin core. Tolyl and ethyl-4(4-butyryl)oxyphenyl) moieties at the meso positions present a bathochromic shift of the absorption bands, and a notable increase in the absorption coefficient of the Q(0,0) and Q(0,1) bands was observed with a higher fluorescence quantum yield and lifetime compared with the free base porphyrin. The electrochemical investigation shows a reversible reduction of the synthesized complexes. The catalytic power and the adsorption properties of the prepared complexes were studied for Calmagite degradation, an azoic organic dye. The results reveal that the studied compounds could be used as catalysts for the decolourisation of dyes in the presence of H2O2.

β-Functionalized trans-A2B2 push–pull tetrabenzoporphyrins

The synthesis of push–pull A2B2 tetrabenzoporphyrins was achieved. These porphyrins exhibit unique patterns of UV-Vis absorptions and emissions.

Monobenzoporphyrins as Sensitizers for Dye-Sensitized Solar Cells: Observation of Significant Spacer-Group Effect

A series of monobenzoporphyrins (WH1-WH4) bearing different conjugated spacer groups were designed and synthesized as sensitizers for dye-sensitized solar cells. Although a phenyl spacer only has a minimal impact on the absorption bands of the monobenzoporphyrin, an ethynylphenyl (WH3) or a vinyl (WH4) spacer redshifts and broadens the absorption bands of the dyes to result in much enhanced light-harvesting ability. Dye-sensitized solar cells based on these monobenzoporphyrin dyes displayed remarkable differences in power conversion efficiencies (PCEs). The monobenzoporphyrin bearing no spacer (WH1) resulted in a PCE of only 0.5 %; in contrast, the monobenzoporphyrin bearing vinyl spacers (WH4) achieved a PCE of 5.2 %. The high efficiency of the WH4 cell is attributed to the higher light-harvesting ability, the lesser extent of aggregation on the TiO2 surface, and the more favorable electron-density distributions of the HOMO and LUMO for electron injection and collection. This work demonstrates the exceptional tunability of benzoporphyrins as sensitizers for dye-sensitized solar cells.

NIR bacteriochlorin chromophores accessed by Heck and Sonogashira cross-coupling reactions on a tetrabromobacteriochlorin derivative

The synthesis of a new tetrabromobacteriochlorin BCBr4 is reported. Pd cross-coupling reactions yielded tetra-coupled products with a significant red shift in the UV-Vis bands.

Pentacene-fused diporphyrins

In this work, we report the synthesis, spectroscopic characterization, and theoretical analysis of a linearly conjugated pentacene-fused porphyrin dimer and cross-conjugated quinone-fused dinaphtho[2,3]porphyrins. These multichromophoric systems display non-typical UV-visible absorptions of either porphyrins or pentacenes/quinones. UV-visible, emission and magnetic circular dichroism (MCD) spectroscopy suggest strong electronic interactions among the multichromophores in the system. DFT calculations revealed the delocalization of the HOMOs and LUMOs spanning the entire dimer and linker assembly. The pentacene-fused porphyrin dimer is significantly more stable than both the corresponding pentacene and the heptacene derivatives. The availability of these huge π-extended and electronically highly interactive multichromophoric systems promises unprecedented electronic and photophysical properties.

Syntheses and Functionalizations of Porphyrin Macrocycles

Porphyrin macrocycles have been the subject of intense study in the last century because they are widely distributed in nature, usually as metal complexes of either iron or magnesium. As such, they serve as the prosthetic groups in a wide variety of primary metabolites, such as hemoglobins, myoglobins, cytochromes, catalases, peroxidases, chlorophylls, and bacteriochlorophylls; these compounds have multiple applications in materials science, biology and medicine. This article describes current methodology for preparation of simple, symmetrical model porphyrins, as well as more complex protocols for preparation of unsymmetrically substituted porphyrin macrocycles similar to those found in nature. The basic chemical reactivity of porphyrins and metalloporphyrin is also described, including electrophilic and nucleophilic reactions, oxidations, reductions, and metal-mediated cross-coupling reactions. Using the synthetic approaches and reactivity profiles presented, eventually almost any substituted porphyrin system can be prepared for applications in a variety of areas, including in catalysis, electron transport, model biological systems and therapeutics.

meso-Tetraphenylbenzoporphyrin-2(2),2(3)-dicarboxylic anhydride: a platform to benzoporphyrin derivatives

A method to synthesize meso-tetraphenylbenzoporphyrin-2(2),2(3)-dicarboxylic anhydride is reported. This compound reacts with alkylamines and arylamines to afford the corresponding "phthalimides" in moderate to excellent yields. The reaction of the title compound with benzene-1,4-diamine or with benzene-1,3-diamine yields the corresponding N,N'-(phenylene)bisphthalimides, whereas with benzene-1,2-diamine or naphthalene-1,8-diamine it affords heterocyclic-fused porphyrins. Molecular mechanics simulations elucidates the multiplicity of signals observed in the NMR spectra of the N,N'-(1,4-phenylene)bisphthalimide 11. This molecule exhibits two preferential conformations corresponding to a coplanar and an almost perpendicular arrangement of the benzoporphyrin units relative to the central benzenic ring.