Bashyam Sridevi

Sapphyrin Supramolecules through C−H⋅⋅⋅S and C−H⋅⋅⋅Se Hydrogen Bonds—First Structural Characterization of meso- Arylsapphyrins Bearing Heteroatoms

An unprecedented coupling reaction of heteroatom-containing tripyrranes leads to the formation of core-modified sapphyrins 1 and 2, which self-assemble in the solid state to form supramolecular ladders. Weak C-H⋅⋅⋅S and C-H⋅⋅⋅Se hydrogen-bonding interactions in addition to C-H⋅⋅⋅N hydrogen bonds are responsible for the observed structures.

Spectroscopic and electrochemical studies on oxaporphyrins and oxathiaporphyrins

The synthesis and characterization of oxaporphyrins (OTPP and O2TPP) containing one and two furan rings in place of pyrrole and a mixed oxathiaporphyrin (OSTPP) is reported. Spectroscopic and electrochemical studies reveal that oxaporphyrins exhibit optical and emission characteristics closer to the parent H2TPP, while their electrochemical behaviour parallels that reported for mono and dithiaporphyrins. However the characteristics of the mixed oxathia derivative resemble that of monothiaporphyrin. Protonation studies reveal weaker resonance interaction between the β-hydrogens and meso-phenyl substituents in sharp contrast to thiaporphyrins. The reduction potentials for OSTPP and O2TPP indicate stabilization and destabilization of their LUMOs relative to the parent H2TPP in the ground and excited states, respectively.

Core Modified meso‐Aryl Corrole: First Examples of CuII, NiII, CoII and RhI Complexes

A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the alpha-alpha coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Nil(II), Cu(II), and Co(II) with the participation of all heteroatoms in the coordination. However, Rh(I) ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni(II) and Rh(I) complexes reveal square planar geometry completed by two CO molecules for Rh(I). The EPR spectra of the paramagnetic that Cu(II) and Col(II) complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the Cu(II) complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO.

One step synthesis of sapphyrin and N-confused porphyrin using dipyrromethane

Reaction of dipyrromethane in trifluoroacetic acid produces sapphyrin while the same reaction in toluene p-sulfonic acid gave N-confused porphyrin.

Durch C−H⋅⋅⋅S- und C−H⋅⋅⋅Se-Brücken stabilisierte Sapphyrin-Supermoleküle – erste strukturelle Charakterisierung von Heteroatome enthaltenden meso-Arylsapphyrinen

Eine unerwartete Kupplungsreaktion heterosubstituierter Tripyrrane lieferte die Sapphyrin-Analoga 1 und 2, die im Kristall supramolekulare Leitern bilden. Schwache C−H⋅⋅⋅S- bzw. C−H⋅⋅⋅Se-Brucken sind neben den ublicheren C−H⋅⋅⋅N-Brucken entscheidend fur das Auftreten dieser Strukturen.

Improved synthesis of meso substituted 21-Oxa and 21-Thia tetra phenyl porphyrins

Abstract An efficient method for the exclusive formation of 21-Oxa and 21-Thia tetra phenyl porphyrins in high yields by condensation of dipyrromethane and furan or thiophene diols is described.

Structural Diversity in Rubyrins: X-ray Structural Characterisation of Planar and Inverted Rubyrins

Meso aryl rubyrins exhibit three different structures. A planar (7) and two unusual inverted structures (8 and 9) have been characterised by X-ray and NMR spectroscopy.

Ground and excited state dynamics of core-modified normal and expanded porphyrins

Singlet and triplet excited state data on two new core-modified expanded porphyrins and their protonated derivatives are reported. Absorption spectral studies indicate a gradual red shift of the absorption bands upon sulfur substitution into the core. The singlet lifetimes for expanded S3-sapphyrin and S4-rubyrin decrease steadily relative to STPPH and S2TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S3-sapphyrin and S4-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M−1 respectively. However, the triplet lifetime for S3-sapphyrin is longer (58.80 μs) than for normal thiaporphyrins (STPPH, 37.45 μs; S2TPP, 20.96 μs), suggesting that it could be very well suited for photosensitizing triplet oxygen.

Spectral, magnetic and electrochemical properties of metal oxa- and oxathia-porphyrins

Metal derivatives (CuII, NiII) of monooxa-, dioxa- and oxathia-tetraphenylporphyrins and their one-electron oxidised and reduced species have been studied. Electronic spectra of the monooxa and oxathia derivatives exhibit split Soret bands and a complicated pattern of Q-bands revealing their lower symmetry. The spectra of one-electron reduced species show only marginal shifts while the one-electron oxidised product of copper monooxaporphyrins show broad, red-shifted bands. Cyclic voltammetric studies indicated one-electron metal-centered reduction at fairly low potentials forming copper(I) and nickel(I) porphyrins. The ring-oxidised product exhibits weak antiferromagnetic interaction between the unpaired electrons of copper and the porphyrin ring. The ESR spectra of the copper dioxa- and oxathia-porphyrins exhibit rhombic symmetry with unusually small metal hyperfine couplings. A comparison of ACu values and the E½ values for metal reduction suggests that distortion towards tetrahedral symmetry and the presence of a soft donor atom like sulfur in porphyrins are required to generate spectral and electrochemical properties like those observed for the type I copper center in proteins.