Studies on cobalt(II), nickel(II) and copper(II) derivatives of some new meso-aryl substituted octabromoporphyrins

A series of Co(II), Ni(II) and Cu(II) derivatives of a variety of porphyrins with tolyl (MTxTP) and naphthyl moieties (MNxTP) as meso-substituents and their octabromoderivatives (MTxOBP and MNxOBP) by Br-substitution at the eight β-pyrrole positions were synthesised and characterised. The changes observed in their electronic spectra are explained in terms of the energy level re-ordering of the HOMO and LUMO levels due to electron withdrawing Br substituents and the concerted action of eight bulky Br atoms bringing about distortional change on the π-framework, and also due to the mesomeric effect due to meso-aryl moieties. The EPR spectra of the Cu(II) derivatives of bromoporphyrins have their spin-Hamiltonian parameters altered when compared to their nonbrominated analogues indicating pronounced electron spin delocalisation on the porphyrinato moiety.