Redox control of photoinduced electron transfer in axial terpyridoxy porphyrin complexes.

The photophysical properties of axial-bonding types (terpyridoxy)aluminum(III) porphyrin (Al(PTP)), bis(terpyridoxy)tin(IV) porphyrin (Sn(PTP) 2), and bis(terpyridoxy)phosphorus(V) porphyrin ([P(PTP) 2] (+)) are reported. Compared with their hydroxy analogues, the fluorescence quantum yields and singlet-state lifetimes were found to be lower for Sn(PTP) 2 and [P(PTP) 2] (+), whereas no difference was observed for Al(PTP). At low temperature, all of the compounds show spin-polarized transient electron paramagnetic resonance (TREPR) spectra that are assigned to the lowest excited triplet state of the porphyrin populated by intersystem crossing.

A colorimetric chemosensor for both fluoride and transition metal ions based on dipyrrolyl derivative.

The synthesis, characterization and ion binding studies of 2,3-di(1H-2-pyrrolyl)pyrido[2,3-b]pyrazine (1) have been described. 1, which has been targeted with a view to sensing both F- and transition metal ions, exhibits binding-induced color changes from yellowish green to red/brown observable by the naked eye. The binding site for the metal ion in the system has been unambiguously established by single-crystal X-ray diffraction study of a Ni(II) complex of 1.

Axial bis(terpyridoxy)phosphorus(V) porphyrin: modulation of PET and EET by Zn2+ or Cd2+ ions.

A novel phosphorus(V) porphyrin bearing two ptp[4'-(4-phenyloxy)-2,2'ratio6',2''-terpyridine] groups was prepared and modulation of the intramolecular PET (lambda(ex)= 566 nm) and PET --> EET (lambda(ex)= 300 nm) processes was studied from ptp to phosphorus(V) porphyrin by Zn2+ or Cd2+ ions.

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions.

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2'-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields.

Crystal structures of the PNA-porphyrin complex in the presence and absence of lactose: mapping the conformational changes on lactose binding, interacting surfaces, and supramolecular aggregations.

The extraordinary recognition specificity of lectins for carbohydrate ligands appears to be violated as they also bind to porphyrins and other noncarbohydrate ligands. In this study, crystal structures of meso-tetrasulfonatophenylporphyrin (H(2)TPPS) bound to peanut agglutinin (PNA) in the presence and absence of lactose were determined. The binding of H(2)TPPS with PNA involved 11 molecules of H(2)TPPS in different supramolecular stacking arrangements associated with a tetramer of PNA in the crystals of the PNA-H(2)TPPS binary complex as well as the PNA-H(2)TPPS-lactose ternary complex.

Thermodynamic analysis of porphyrin binding to Momordica charantia (bitter gourd) lectin.

Owing to the use of porphyrins in photodynamic therapy for the treatment of malignant tumors, and the preferential interaction of lectins with tumor cells, studies on lectin-porphyrin interaction are of significant interest. In this study, the interaction of several free-base and metalloporphyrins with Momordica charantia (bitter gourd) lectin (MCL) was investigated by absorption spectroscopy. Difference absorption spectra revealed that significant changes occur in the Soret band region of the porphyrins on binding to MCL.

DNA interactions of new mixed-ligand complexes of cobalt(III) and nickel(II) that incorporate modified phenanthroline ligands.

Four new mixed-ligand complexes, namely [Co(phen)(2)(qdppz)](3+), [Ni(phen)(2)(qdppz)](2+), [Co(phen)(2)(dicnq)](3+) and [Ni(phen)(2)(dicnq)](2+) (phen=1,10-phenanthroline, qdppz=naptho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine-5,18-dione and dicnq=dicyanodipyrido quinoxaline), were synthesized and characterized by FAB-MS, UV/Vis, IR, 1H NMR, cyclic voltammetry and magnetic susceptibility methods. Absorption and viscometric titration as well as thermal denaturation studies revealed that each of these octahedral complexes is an avid binder of calf-thymus DNA. The apparent binding constants for the dicnq- and qdppz-bearing complexes are in the order of 10(4) and >10(6) M(-1), respectively.

Enhanced optical limiting and nonlinear absorption properties of azoarene-appended phosphorus (V) tetratolylporphyrins.

Optical limiting performance, third-order nonlinearity chi(3), and nonlinear absorption properties have been investigated in a new class of azoarene phosphorus (V) porphyrins with charge transfer (CT) states. The introduction of axial azoarene groups into the phosphorus porphyrin structure is found to reduce the limiting threshold by a factor of 2 and lead to a rise in the second hyperpolarizability by 1 order of magnitude in the picosecond time regime and by 2 orders of magnitude in the nanosecond regime. The experimental data show reverse saturation of absorption in the nanosecond time regime and a saturation of the nonlinear absorption above a fluence of 0.

New insight into the synthesis of a novel azo-based optically active polyamidoamine side chain dendritic polyester architectural photoswitch.

[reaction: see text] A novel chiral polyamidoamine side chain dendritic polyester 4 has been synthesized and found to be a photoresponsive system undergoing reversible E/Z photochemical/thermal isomerization of azo units. Thorough characterization (IR,UV-vis, NMR, FAB-MS, elemental analysis, optical rotation, etc.) were performed to ascertain the structures of dendrimers 2, 3, and 4.

"Axial-Bonding"-Type Hybrid Porphyrin Arrays: Synthesis, Spectroscopy, Electrochemistry, and Singlet State Properties.

A series of phosphorus(V), germanium(IV), and tin(IV) porphyrin-based, "axial-bonding"-type hybrid trimers have been readily constructed by employing a new "building-block" approach. The approach is modular in nature, and it involves simple "inorganic" reactions such as axial bond formation of main group element containing porphyrins and insertion of metal/"metalloid" ions into the porphyrin cavity. The architecture of these arrays is such that, while a phosphorus(V), germanium(IV), or tin(IV) complex of meso-5,10,15,20-(tetratolyl)porphyrin forms the basal scaffolding unit, the free-base, vanadyl, cobalt(II), nickel(II), copper(II), or zinc(II) porphyrins occupy the two axial sites via an aryloxy bridge.

Aryloxo Derivatives of Phosphorus(V) Porphyrins. Synthesis, Spectroscopy, Electrochemistry, and Singlet State Properties.

Aryloxo derivatives of phosphorus(V) porphyrins of the type [(TpTP)P(OR)(2)](+)OH(-) where TpTP is the dianion of tetra-p-tolylporphyrin and OR is an axial aryloxo (2,4-dimethylphenoxo, 4-methylphenoxo, phenoxo, 4-nitrophenoxo, 4-(4-nitrophenoxy)phenoxo, or 4-(2,4-dinitrophenoxy)phenoxo) ligand have been synthesized and fully characterized by FAB-mass, UV-vis, fluorescence, infrared, and nuclear magnetic resonance ((1)H and (31)P) spectroscopies and cyclic voltammetric methods. Each new porphyrin shows a typical "normal UV-vis absorption spectrum" indicating the presence of a P(V) ion in the porphyrin cavity. The proton-decoupled (31)P NMR signal observed for these compounds, between -194 and -200 ppm, suggests that there exists an octahedral coordination around the phosphorus atom, and this supposition is further substantiated by the porphyrin ring-current-induced upfield shifts observed for protons on the two axial aryloxo ligands in the (1)H NMR spectra.