An efficient and rapid method of preparation of pheophytina from leaves using silica gel as column material is described. The different divalent metallo, Co, Ni, Cu and Zn derivatives of pheophytin have been prepared and characterised. The optical absorption and emission, and¹Hnmr spectral data of pheophytina and its metal derivatives are presented

Molecular association of porphyrins and their metal derivatives has been recognized as one of the important properties for many of their biological functions. The association is classified into (i) self-aggregation, (ii) intermolecular association and (iii) intramolecular association. The presence of metal ions in the porphyrin cavity is shown to alter the magnitudes of binding constants and thermodynamic parameters of complexation. The interaction between the porphyrin unit and the acceptor is described in terms of π-π interaction. The manifestation of charge transfer states both in the ground and excited states of these complexes is shown to influence the rates of excited state electron transfer reactions. Owing to paucity of crystal structure data, the time-averaged geometries of many of these complexes have been derived from magnetic resonance data.

Buckminsterfullerene, obtained in good yields at high rates by a suitably designed generator, has been characterized by electron microscopy and in terms of an approximate energy level diagram; C₆₀ undergoes four reversible one-electron reductions giving rise to anionic species and interacts with tetrathiafulvalene to form a charge-transfer complex in the ground state.

Synthesis of the free-basetetrakis (3′-nitro/aminophenyl), (H₂TNP/ H₂TAP) has been accomplished and its coordination behaviour towards Mg(II), Co(II), Zn(II) and Ag(II) ions is investigated. Optical and magnetic resonance properties of the metal derivatives MTNP and MTAP reveal that the aminoporphyrins exist as aggregates in solution. The aggregation is promoted by the coordination of the peripheral amino groups to neighbouring metalloporphyrins. Possible structures of aggregated species are proposed from the model studies.

This article presents a brief overview of different kinds of silanols and the important reactions of N-bonded silanetriols. The synthesis and characterization of silanediols containing Si-N and Si-C bonds, (2,4,6-Me₃C₆H₂)N(SiMe₃)Si(Me)(OH)₂ (1e) is described. 1e shows a polymeric crinkled tape type of structure due to extensive intermolecular hydrogen bonding. We also describe the formation of a neutral copper(II) complex derived from the reaction of CuCl₂ with (O)P(3,5-Me₂Pz)₃ where the ligand undergoes a facile P-N bond cleavage and functions as an N₂O type of tridentate ligand.

A series of covalently linked bisporphyrins bearingmeso-tetraphenylporphyrin (TPP) and octabromotetraphenylporphyrin (OBTPP) units have been synthesised and characterised. Electrochemical studies on these bisporphyrins showed an anodic shift (∼ 30–60 mV) of the TPP unit and a cathodic shift (∼40-80 mV) of OBTPP in redox potentials. Further, steady-state fluorescence studies on bisporphyrins indicated dramatic decrease in fluorescence quantum yields of the TPP moiety. Electrochemical redox and fluorescence data seem to suggest the possible existence of intramolecular interactions in these bisporphyrins

Bicovalently linked tetraphenylporphyrins bearing dioxypentane groups at the opposite (transoid, H₄A) and adjacent (cisoid, H₄B) aryl groups have been synthesised. Protonation of the free-base porphyrins leads to fully protonated species H₈A⁴⁺/H₈A⁴⁺ accompanied by expansion of cavity size of the bisporphyrins. The electrochemical redox studies of these porphyrins and their Zinc(II) derivatives revealed that the first ring oxidation proceeds through a two-electron process while the second ring oxidation occurs at two distinct one-electron steps indicating unsymmetrical charge distribution in the oxidized intermediate. The axial ligation properties of the Zinc(Il) derivatives of H₄A/H₄B with DABCO and PMDA investigated by spectroscopic and single crystal X-ray diffraction studies showed predominant existence of 1 : I complex. The Zn₂A.DABCO complex assumes an interesting eclipsed structure wherein DABCO is located inside the cavity between the two porphyrin planes with Zn-N distances at 2.08 and 2.22 Å. The Zn atoms are pulled into the cavity due to coordination towards nitrogen atoms of DABCO and deviate from the mean porphyrin plane by 0.35 Å. The electrochemical redox potentials of the axially ligated metal derivatives are found to be sensitive function of the relative coordinating ability of the ligands and the conformation of the hosts.