A theoretical study of subphthalocyanine and its nitro- and tertbutyl-derivatives

The unsubstitute subphthalocyanine (SubPc) and their tertbutyl- (tertbutyl- SubPc) and nitro-(nitro-SubPc) derivatives have been theoretically studied at Hartree-Fock (HF) and Density Functional Theory (DFT) levels using STO-3 G and 6-31G basis sets. The geometric optimization of the molecules was car ried out. The calculated geometry for SubPc agrees with experimental X-ray data. No significant geometrical changes with respect to SubPc were observe d in the tertbutyl-SubPc and nitro-SubPc macrocycles. B-Cl distance systema tically changes with the electron donor/acceptor properties of the peripher al substituents. The calculated dipole moments reproduce very well the expe rimental values, whereas the atomic charges reveal the polar character of t he SubPc macrocycle. An extensive study of some frontier orbitals was perfo rmed. The present calculations reproduce the breakdown of Gouterman's four- orbital model in SubPcs, this effect being less dramatic in the DFT descrip tion. The nodal patterns for the two highest occupied molecular orbitals an d the two lowest unoccupied molecular orbitals obtained from different comp utational methods exhibit important differences, but in general an explanat ion for some of the most important aspects of the chemical reactivity of th e SubPcs can be put forward. (C) 2001 Elsevier Science B.V. All rights rese rved.