Core-modified porphyrins: novel building blocks in chemistry

Various (metallo)porphyrins and related compounds have been intensively investigated by different research groups due to their extremely important role in living organisms along with their versatile applications in technology. The design of novel porphyrinoids by core-modification, or substitution of pyrrole nitrogens, with the elements of other groups of the Periodic Table has been considered as a highly promising methodology for tuning structures and properties of porphyrinoids and thus opening new possible applications for them. Much effort has been given to the modifications of the porphyrin core with elements of the main groups, namely O, S, Se (chalcogens), and the heavier congener of nitrogen, phosphorus. In general, the porphyrin core modification by replacing nitrogens with heteroatoms is a promising and effective strategy for obtaining new compounds with unusual structures and properties (optical, electrochemical, coordinating, etc.) as well as reactivity. These novel molecules can also be employed as promising building or construction blocks in various applications in the nanotechnology area.

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.

Bis(1-methylimidazole)[meso-α,α,α,α-tetrakis(o-nicotinamidophenyl)porphinato]iron(II)–1-methylimidazole–tetrahydrofuran (1/1/1.5)

In the title compound, [FeII(C68H44N12O4)(C4H6N2)2]·C4H6N2·1.5C4H8O, the central FeII ion is coordinated by four pyrrole N atoms of the porphyrin core and two N atoms of the 1-methylimidazole ligands in the axial sites. One 1-methylimidazole and one and a half tetrahydrofuran solvent molecules are also present in the asymmetric unit. The complex exhibits a near planar porphyrin core conformation, in which the iron centre is slightly displaced towards the hindered porphyrin side (0.01 Å). The average Fe—Np (Np refers to the pyrrole nitrogen atoms in the porphyrin) bond length is 1.990 (9) Å, and the axial Fe—NIm (NIm refers to the imidazole nitrogen atoms) bond lengths are 1.993 (3) and 2.004 (3) Å. The dihedral angle between the two coordinated 1-methylimidazole planes is 56.6 (2)°. The dihedral angles between the 1-methylimidazole planes and the planes of the closest Fe—Np vector are 16.8 (2) and 39.8 (2)°. N—H...N and N—H...O interactions are observed in the crystal structure.

Comparison of P- and As-core-modified porphyrins with the parental porphyrin: a computational study

The first comparative DFT (B3LYP/6-31G*) study of the Zn-porphyrin and its two derivatives, ZnP(P)4 and ZnP(As)4, is reported. For all three species studied, ZnP, ZnP(P)4 and ZnP(As)4, the singlet was calculated to be the lowest-energy structure and singlet-triplet gap was found to decrease from ca. 41—42 kcal/mol for N to ca. 17—18 kcal/mol for P and to ca. 10 kcal/mol for As. Both ZnP(P)4 and ZnP(As)4 were calculated to attain very pronounced bowl-like shapes. The frontier molecular orbitals (MOs) of the core-modified porphyrins are quite similar to the ZnP frontier MOs. For the HOMO-2 of the core-modified porphyrins due to the ZnP(P)4/ZnP(As)4 bowl-like shapes we might suppose the existence of “internal” electron delocalization inside the ZnP(P)4/ZnP(As)4 “bowls”. Noticeable reduction of the HOMO/LUMO gaps was calculated for ZnP(P)4 and ZnP(As)4, by ca. 1.10 and 1.47 eV, respectively, compared to ZnP. The core-modification of porphyrins by P and especially by As was found to result in significant decrease of the charge on Zn-centers, by ca. 0.61—0.67e for P and by ca. 0.69—0.76e for As. Charges on P- and As-centers were computed to have large positive values, ca. 0.41—0.45e and ca. 0.43—0.47e, for P and As, respectively, compared to significant negative values, ca. −0.65 to −0.66e for N. The porphyrin core-modification by heavier N congeners, P and As, can noticeably modify the structures, electronic, and optical properties of porphyrins, thus affecting their reactivity and potential applications.

Synthesis and Photostability of Cyclooctatetraene-Substituted Free Base Porphyrins

A series of free base meso-tetraarylporphyrins functionalized with substituents containing one, two, and four cyclooctatetraene (COT) moieties have been obtained and characterized by spectral and photophysical studies. Three COT-free porphyrins served as reference compounds. COT is a triplet quencher, well-known to enhance the photostability of several, but not all, fluorophores. In the case of porphyrins, substitution with COT improves photostability in zinc derivatives, but for free bases, the effect is the opposite. We show that placing the COT moiety further from the free base porphyrin core enhances the photostability when the COT group lies in the direct vicinity of the macrocycle. The quantum yields of photobleaching inversely correlate with porphyrin oxidation potentials. An improvement in photostability in both COT-containing and COT-free porphyrins can be achieved by screening the porphyrin core from oxygen by switching from tolyl to mesityl substituents. This leads to a decrease in the photobleaching quantum yield, even though triplet lifetimes are longer. The results confirm the involvement of oxygen in the photodegradation of porphyrins.

The influence of triphenylamine as a donor group on Zn–porphyrin for dye sensitized solar cell applications

Novel donor–π–acceptor based Zn–porphyrins (Ko-1 and Ko-2) have been designed and synthesized. Triphenylamine (TPA) was introduced instead of hydrogen in the porphyrin core. A solar cell efficiency was achieved that was almost equal to N719 dye.

Arylphosphonate-Tethered Porphyrins: Fluorescence Silencing Speaks a Metal Language in Living Enterocyte

<p>We report the application of a highly versatile and</p> <p>engineerable novel sensor platform to monitor biologically significant</p> <p>and toxic metal ions in live human Caco-2 enterocytes. The extended</p> <p>conjugation between the fluorescent porphyrin core and metal ions via</p> <p>aromatic phenylphosphonic acid tethers generates a unique turn off</p> <p>and turn on fluorescence and, in addition, shifts in absorption and</p> <p>emission spectra for zinc, cobalt, cadmium and mercury. The reported</p> <p>fluorescent probes p-H8TPPA and m-H8TPPA can monitor a wide</p> <p>range of metal ion concentrations via fluorescence titration and also</p> <p>via fluorescence decay curves. Cu and Zn-induced turn off</p> <p>fluorescence can be differentially reversed by the addition of common</p> <p>chelators. Both p-H8TPPA and m-H8TPPA readily pass the</p> <p>mammalian cellular membrane due to their amphipathic character as</p> <p>confirmed by confocal microscopic imaging of living enterocytes.</p>

Arylphosphonate-Tethered Porphyrins: Fluorescence Silencing Speaks a Metal Language in Living Enterocyte

<p>We report the application of a highly versatile and</p> <p>engineerable novel sensor platform to monitor biologically significant</p> <p>and toxic metal ions in live human Caco-2 enterocytes. The extended</p> <p>conjugation between the fluorescent porphyrin core and metal ions via</p> <p>aromatic phenylphosphonic acid tethers generates a unique turn off</p> <p>and turn on fluorescence and, in addition, shifts in absorption and</p> <p>emission spectra for zinc, cobalt, cadmium and mercury. The reported</p> <p>fluorescent probes p-H8TPPA and m-H8TPPA can monitor a wide</p> <p>range of metal ion concentrations via fluorescence titration and also</p> <p>via fluorescence decay curves. Cu and Zn-induced turn off</p> <p>fluorescence can be differentially reversed by the addition of common</p> <p>chelators. Both p-H8TPPA and m-H8TPPA readily pass the</p> <p>mammalian cellular membrane due to their amphipathic character as</p> <p>confirmed by confocal microscopic imaging of living enterocytes.</p>