Synthesis and Photophysical Investigation of New Porphyrin Derivatives with β-Pyrrole Ethynyl Linkage and Corresponding Dyad with [60] Fullerene

Synthesis and Biological Properties of EGFR-Targeted Photosensitizer Based on Cationic Porphyrin

Photodynamic therapy (PDT) in oncology is characterized by low invasiveness, minimal side effects, and little tissue scarring. Increasing the selectivity of PDT agents toward a cellular target is a new approach intended to improve this method. This study is devoted to the design and synthesis of a new conjugate based on meso-arylporphyrin with a low-molecular-weight tyrosine kinase inhibitor, Erlotinib. A nano-formulation based on Pluronic F127 micelles was obtained and characterized. The photophysical and photochemical properties and biological activity of the studied compounds and their nano-formulation were studied. A significant, 20-40-fold difference between the dark and photoinduced activity was achieved for the conjugate nanomicelles. After irradiation, the studied conjugate nanomicelles were 1.8 times more toxic toward the EGFR-overexpressing cell line MDA-MB-231 compared to the conditionally normal NKE cells. The IC50 was 0.073 ± 0.014 μM for the MDA-MB-231 cell line and 0.13 ± 0.018 μM for NKE cells after irradiation for the target conjugate nanomicelles.

Design of A3B-Porphyrin Conjugates with Terpyridine as Potential Theranostic Agents: Synthesis, Complexation with Fe(III), Gd(III), and Photodynamic Activity

This paper reports on the design and synthesis of new multifunctional porphyrin-based therapeutic agents for potential therapeutic and diagnostic applications. Zinc complexes of A3B-type meso-arylporphyrins containing OH- and COOH- groups were modified with chelating ligands based on 4'-(4-methylphenyl)-2,2':6',2″-terpyridine derivatives in high yields. Novel complexes with Gd(III), Fe(III) were obtained for these conjugates. Aggregation behaviour in solutions of different solubilisers was studied to inform the selection of the optimal solubilising platform for the porphyrins obtained; their photophysical and photochemical properties were also characterised. Micellar Pluronic F127 formulation was found to be the most effective solubiliser for stabilising the fluorescence-active monomolecular form of the photosensitisers (PS). In vitro cytotoxicity of the compounds was studied on the HEP-2 cell line with and without irradiation for 1.5 and 24 h. As a result, the IC50 of compounds 12 and 14 at an irradiation dose of 8.073 J/cm2 was shown to be 1.87 ± 0.333 and 1.4 ± 0.152 μM, respectively; without irradiation, the compound had no toxic effect within the studied concentration range (1.5 h). A test for the inhibition of metabolic cooperation or promoter activity was also performed for the abovementioned compounds, showing the efficacy and safety of the conjugates obtained. Preliminary data have indicated the high potential of the new type of PS to be promising molecular theranostic agents.

Unsymmetrically β-Functionalized π-Extended Porphyrins: Synthesis, Spectral, Electrochemical Redox Properties, and Their Utilization as Efficient Two-Photon Absorbers

Two new series of unsymmetrically β-functionalized porphyrins, MTPP(NO₂)MA (1M), (MA = methyl acrylate) and MTPP(NO₂)MB (2M) (MB = mono-benzo) (where M = 2H, Co(II), Ni(II), Cu(II) and Zn(II)), were synthesized and characterized by various spectroscopic techniques. The saddle shape conformation of ZnTPP(NO₂)MAPy and ZnTPP(NO₂)MB was confirmed by single-crystal X-ray analysis. Density functional theory (DFT) calculation revealed that NiTPP(NO₂)MB has a severe nonplanar geometry possessing a high magnitude of ΔC_β = ±0.727 Å and Δ24 = ±0.422 Å values among all other porphyrins. Synthesized β-substituted porphyrins exhibited red-shifted B- and Q-bands corresponding to their parent molecule due to the electron-withdrawing peripheral substituents. Notable redshift (Δλ_max = 50-60 nm) in electronic spectral features and with weak-intensity emission spectral features were observed for the free-base porphyrins and Zn(II) complexes compared to H₂TPP and ZnTPP, respectively. The first-ring reduction potential of MTPP(NO₂)MA (1M) exhibited 0.21-0.5 V anodic shift, whereas 0.18-0.23 V anodic shift was observed in the first-ring oxidation potential compared to the corresponding MTPPs due to the presence of electron-withdrawing β-substituents at the periphery of the macrocycle. Interestingly, NiTPP(NO₂)MA (1Ni) has shown an additional Ni^II/Ni^III oxidation potential observed at 2.05 V along with two ring-centered oxidations. The first-ring reduction and oxidation potentials of MTPP(NO₂)MB (2M) have shown 0.39-0.46 and 0.19-0.27 V anodic shifts with respect to their corresponding MTPPs. The nonlinear optical (NLO) properties of all of the porphyrins were investigated, and the extracted nonlinear optical parameters revealed intense reverse-saturable absorption (RSA) behavior and the self-focusing behavior with positive nonlinear refractive index in the range of (0.19-1.75) × 10^-17 m²/W. Zn(II) complexes exhibited the highest two-photon absorption coefficient (β) and cross section (σ_TPA) of ∼95 × 10^-12 m/W and 19.66 × 10⁴ GM, respectively, among all of the metal complexes.

Probing Charge Management across the π-Systems of Nanographenes in Regioisomeric Electron Donor-Acceptor Architectures

Inspired by light-induced processes in nature to mimic the primary events in the photosynthetic reaction centers, novel functional materials combine electron donors and acceptors, i.e., (metallo)porphyrins (ZnP) and fullerenes (C₆₀), respectively, with emerging materials, i.e., nanographenes. We utilized hexa-peri-hexabenzocoronene (HBC) due to its versatility regarding functionalization and physicochemical properties, to construct three regioisomeric ZnP-HBC-C₆₀ conjugates, which foster geometrical diversity by arranging ZnP and C₆₀ in ortho-, meta-, and para-positions to each other. The corresponding hexaarylbenzene (HAB) motifs, with an interrupted π-system, were also prepared. Transient absorption measurements disclosed the fast population of charge transfer as well as singlet and triplet charge-separated states. With the help of density functional theory (DFT) calculations, we further conceive the communication across the HBCs and HABs. This work reveals the impact of both the geometrical arrangement with respect to through-space versus through-bond interactions and the structural rigidity/flexibility on the charge management across the different π-systems.

A covalent cobalt diimine-dioxime - fullerene assembly for photoelectrochemical hydrogen production from near-neutral aqueous media

The covalent assembly between a cobalt diimine-dioxime complex and a fullerenic moiety results in enhanced catalytic properties in terms of overpotential requirement for H₂ evolution. The interaction between the fullerene moiety and PCBM heterojunction further allows for the easy integration of the cobalt diimine-dioxime – fullerene catalyst with a poly-3-hexylthiophene (P3HT):[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) bulk heterojunction, yielding hybrid photoelectrodes for H₂ evolution from near-neutral aqueous solutions.

The covalent assembly between a cobalt diimine-dioxime complex and a fullerenic moiety results in enhanced catalytic properties in terms of overpotential requirement for H₂ evolution and allows its integration in an operating photocathode.

Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(-2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(-2ω; ω, ω)/5kT, as confirmed by computational evidence.

Ethyne Functionalized Meso-Phenothiazinyl-Phenyl-Porphyrins: Synthesis and Optical Properties of Free Base Versus Protonated Species

Synthesis, structural characterization and photophysical properties for a series of new trans-A2B2- and A3B-type ethynyl functionalized meso-phenothiazinyl-phenyl porphyrin derivatives are described. The new compounds displayed the characteristic porphyrin absorption spectra slightly modified by weak auxochromic effects of the substituents and fluorescence emission in the range of 651-659 nm with 11-25% quantum yields. The changes recorded in the UV-vis absorption spectra in the presence of trifluoroacetic acid (TFA) are consistent with the protonation of the two internal nitrogen atoms of the free-base porphyrin (19 nm bathochromic shift of the strong Soret band and one long wave absorption maxima situated in the range of 665-695 nm). Protonation of the phenothiazine substituents required increased amounts of TFA and produced a distinct hypsochromic shift of the long wave absorption maxima. The density functional theory (DFT) calculations of a porphyrin dication pointed out a saddle-distorted porphyrin ring as the ground-state geometry.

Effect of the linkage modes of thiolated ethynyl groups on the spin-dependent electronic transport properties in transition metal porphyrin molecular junctions

Using density functional theory and nonequilibrium Green's function method, the spin-dependent electronic transport properties of six transition metal porphyrin molecules (VP, CrP, MnP, FeP, CoP, and NiP), which are linked to gold electrodes through the thiolated ethynyl groups, are investigated. Two different linkage modes (beta linkage and meso linkage) of the substituted ethynyl groups on the porphyrin macrocycle are considered. The results show that the linkage mode of ethynyl groups plays an important role on the spin transport properties of the molecular junctions and the beta linkage is more favorable for the spin filtering efficiency of current than the meso linkages. The spin-up and spin-down energy levels show the different evolutions which is responsible for the difference of spin filtering efficiency between the two linkage modes. The computational results of total current show that the meso-linked molecular junctions have the better conductive performances than the beta-linked ones which may be caused by the different electronic transport paths.

Rational Synthesis of 2-Bromoporphyrins and 2,12-Dibromoporphyrins

Bromoporphyrins were prepared by the metal-mediated self-condensation of brominated 1-formyldipyrromethanes. Depending on the conditions, Mg(II)-2,12-dibromoporphyrin and Mg(II)-2-bromoporphyrin could be obtained in up to 11% and 17% isolated yield, respectively. Zn(II) was also a viable templating metal. The positions of the bromine substituents were confirmed by 2D-NMR spectroscopic analysis and the X-ray crystal structure of a derivative. Suzuki and Sonogashira reactions of the bromoporphyrins yielded 2-substituted or 2,12-disubstituted porphyrins with red-shifted absorption and emission spectra. This method provides access to the minimalist core of β-mono- and β,β'-disubstituted porphyrins from readily available starting materials.

Highly reducible π-extended copper corroles

Di- and octa-phenylethynyl (PE) substituted π-extended copper corroles were synthesized and characterized as to their structural, electrochemical and spectroscopic properties. The addition of two or eight PE groups to the β-pyrrole positions of the corrole results in dramatic red shifts in the electronic absorption spectra and new reductions which are not seen for the parent compound lacking PE substituents. CuCor(PE)₈ is reduced in four reversible one-electron transfer steps to give derivatives of [CuCor(PE)₈]^n- where n = 1, 2, 3 or 4. Variable temperature ¹H NMR and EPR measurements were carried out and suggest that the octa- and di-PE substituted Cu-corroles can both be described as an antiferromagnetically coupled Cu^II corrole cation radical which is in equilibrium with a triplet state, possibly due to a lower singlet-triplet energy gap as compared to 1 and 2 at room temperature. The EPR spectra of one-electron oxidized and one electron reduced species exhibited the characteristics of Cu(ii) corroles. The products generated in the first two reductions of each π-extended corrole were characterized by thin-layer spectroelectrochemistry, thus providing new insights into how UV-vis spectra of highly reduced corroles vary as a function of the number of PE groups and overall charge on the molecule. The singly reduced and singly oxidized copper corroles were also chemically generated in CH₃CN and shown to have UV-visible spectra almost identical to the spectra obtained by electroreduction or electrooxidation in PhCN or THF containing 0.1 M tetrabutylammonium perchlorate.

Solid-state inclusion of C60 and C70 in a co-polymer induced by metal–ligand coordination of a Zn–porphyrin cage with a bis-pyridyl perylene derivative

We have conducted X-ray characterization of two unprecedented supramolecular solids involving three different components: a suitable Zn(ii)–bisporphyrin cage, a bis-pyridyl perylene derivative and a fullerene.

Synthesis, properties and singlet oxygen generation of thiazolidinone double bond linked porphyrin at meso and β-position

Meso and β-substituted free base and zinc metallated thiazolidinone–porphyrin conjugates were synthesized by one pot four component Knoevenagel condensation by utilizing substituted amines, carbon disulfide, ethyl chloroacetate and porphyrin aldehydes.

Immobilization of a cobalt catalyst on fullerene in molecular devices for water reduction

A cobalt-based molecular catalyst was successfully grafted to a fullerene derivative via 'click' chemistry on an electrode for both electro-catalytic and light driven water reduction. Using an organic photovoltaic electrode immobilized with a cobalt catalyst as the photocathode, the photoelectrochemical cell displayed a stable photocurrent.

Synthesis and functionalization of β-alkyl-meso-triarylcorroles

After the definition of efficient synthetic routes for the preparation of triarylcorroles, the functionalization of these macrocycles is becoming a necessary and challenging field of research. One important synthetic step is the introduction of substituents able to influence the electronic distribution in the macrocyclic ring. A valuable target would be a corrole macrocycle with some β-pyrrole positions occupied by methyl groups, while exploiting other positions to introduce electron-withdrawing substituents. To explore the scope of this approach, we investigated the bromination and the nitration of the corrole ring and the desired products have been obtained in moderate to good yield. The successful preparation of selectively halogenated corroles is particularly interesting since they are suitable substrates for the preparation of more complex partially alkylated structures using modern cross coupling methodologies.

Photophysical properties of Sn(IV)tetraphenylporphyrin-pyrene dyad with a β-vinyl linker

A Sn (IV)tetraphenylporphyrin (T) has been functionalized with a β-vinyl pyrene (P) and the photophysical properties of the formed dyad (T-P) with its corresponding precursors were studied in three solvents with different polarities using steady-state and time-resolved measurements in ps and fs timescales. When the pyrene moiety is excited at λex = 340 nm, the fluorescence spectroscopy experiments indicate in all the studied solvents, an efficient quenching of the pyrene emission. When excited at either λex = 340 nm or λex = 405 nm, where porphyrin absorbs, a new emissive excited state complex (T-P)* is observed at wavelenghts close to the parent porphyrin emission. The emission is more pronounced in nonpolar hexane showing a mono-exponential decay, but bi-exponential decays are observed in more polar dicloromethane and acetonitrile. When the porphyrin moiety is excited at λex = 425 nm, the fs transient absorption analysis shows two different intermediate species (~ 7–11 ps and 80–100 ps) with broad absorption in the near-IR region. This implies either the existence of two different excited conformers (T-P)*, which decay to the ground state via a charge separated state (CSS), or the formation of the (T-P)* state via the second excited state of the porphyrin moiety, yielding first an excited emissive v(T-P)* state, with a lifetime of 80–100 ps.

Synthesis and photodynamics of diphenylethynyl-bridged porphyrin-quinoidal porphyrin hybrids

As new donor–acceptor hybrids for energy and/or electron transfer, zinc complex and free-base of a porphyrin-quinoidal porphyrin dyad linked by a diphenylethynyl bridge were prepared via Sonogashira and subsequent Takahashi coupling reactions. The quinoidal porphyrin units have two dicyanomethylene groups at the opposite meso-positions. The UV-vis absorption spectra of the dyads were almost linear summations of the absorption spectra of each component in comparison with those of the monomeric reference compounds, indicating very weak electronic interactions between the chromophores at the ground state. Both zinc complex and free-base of the reference porphyrin exhibited fluorescence in the range of ca. 600–700 nm upon photoexcitation, while the quinoidal porphyrin monomers showed no fluorescence. The considerable quenching (more than 99%) of the porphyrin fluorescence in the dyads suggested significant electronic communications between the subunits of the excited state. The electrochemical analysis confirmed that the first oxidations of the dyads occur at the porphyrin units and the first reductions take place at the quinoidal porphyrin units. Femtosecond laser flash photolysis of the zinc dyad with photoexcitation at 393 nm showed both ultrafast (<1 ps) energy and electron transfer from the porphyrin unit to the quinoidal porphyrin one, which processes resulted in the quenching of the porphyrin fluorescence. On the other hand, the free-base dyad underwent only energy transfer.

Synthesis and photophysical properties of β-triazole bridged porphyrin–coumarin dyads

Novel β-triazole bridged porphyrin–coumarin dyads are synthesized via a Cu(i)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction and evaluated for their photophysical properties.

Synthesis, spectroscopic, electrochemical redox, solvatochromism and anion binding properties of β-tetra- and -octaphenylethynyl substituted meso-tetraphenylporphyrins

β-Phenylethynyl (PE) porphyrins exhibited unique photophysical properties and solvatochromic behavior due to ICT from the porphyrin core to PE moieties. Further, Zn(ii) porphyrins were utilized for anion sensing.

β-Substituted ferrocenyl porphyrins: synthesis, structure, and properties

β-Substituted ferrocenyl porphyrins were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The UV-vis absorption, emission, and cyclic voltammetric results indicate strong electronic communication between ferrocene and porphyrin. The porphyrin 4a is non-emissive in nature, while 4b and 4c show reduced fluorescence quantum yield. The single crystal X-ray structure of 4b is reported, which shows extensive C-H-π interactions.

AB INITIO AND DFT THEORETICAL INVESTIGATIONS ON NOVEL PORPHYRIN–FULLERENE SUPRAMOLECULAR DYADS FOR PHOTOVOLTAIC DEVICES

The conformational stability and electronic structures of novel H 2-(1) and Zn-tetraphenylporphyrin–[60]fullerene (2) dyads, in which the [60]fullerene is directly linked to the tetrapyrrolic rings by ethynylenephenylene subunits, have been studied by ab initio and density functional theory calculations. From the investigation on frontier molecular orbitals, it was found that the lowest unoccupied molecular orbital state of these supramolecules is localized on the fullerene and that the highest occupied molecular orbital state is localized on the porphyrin moiety. Molecular electrostatic potential maps clearly demonstrate the electron transfer phenomena from the porphyrin moiety to the fullerene in dyads 1 and 2.

Photoinduced electron transfer in Zn(II)porphyrin-bridge-Pt(II)acetylide complexes: variation in rate with anchoring group and position of the bridge

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the β position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.