V. R. Ferro

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

Abstract 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-3G and 6-31G basis sets. The geometric optimization of the molecules was carried out. The calculated geometry for SubPc agrees with experimental X-ray data. No significant geometrical changes with respect to SubPc were observed in the tertbutyl-SubPc and nitro-SubPc macrocycles. B–Cl distance systematically changes with the electron donor/acceptor properties of the peripheral substituents. The calculated dipole moments reproduce very well the experimental values, whereas the atomic charges reveal the polar character of the SubPc macrocycle. An extensive study of some frontier orbitals was performed. The present calculations reproduce the breakdown of Goutermans four-orbital model in SubPcs, this effect being less dramatic in the DFT description. The nodal patterns for the two highest occupied molecular orbitals and the two lowest unoccupied molecular orbitals obtained from different computational methods exhibit important differences, but in general an explanation for some of the most important aspects of the chemical reactivity of the SubPcs can be put forward.

Molecular electronic structure of subphthalocyanine macrocycles

Quantum chemical calculations at semiempirical (MNDO methods) and ab initio (6-31G and STO-3G basis ses) levels have been performed on boron(III) subphthalocyanines 1-10. Theoretical calculations predict a cone-shaped structure for these compounds independently of the kind of peripheral substitution and even of compositional changes in the central region of the macrocycle (for example, substitution of the boron atom by two hydrogens). The theoretical calculations are in excellent agreement with previous X-ray determinations.

Aromaticity in tautomers of triazoleporphyrazine

The effect of tautomerism on the aromaticity was studied for the free base triazoleporphyrazine at the Density Functional Theory level, using double-zeta double polarized basis sets. The porphyrazine (1), the three tautomers (2a, 2b and 2c) as well as the Ni complex (3) of triazoleporphyrazine were examined. Two independent aromaticity criteria, the geometry-based index HOMA and the magnetic properties-based index NICS, were used to estimate the aromaticity of the complete and selected fragments of the above compounds. Results show that structure 2a, which has the H atom in position 1 of the triazole ring, has low aromaticity, although it contains structural fragments with large conjugation. The aromatic character of both tautomers 2b and 2c is similar to that of both the porphyrin and the porphyrazine. The central ring contour was found to be the most aromatic part of the triazoleporphyrazine tautomers. Occupancy of the central position of the macrocycle cavity of the triazoleporphyrazine by a metal atom increases the aromaticity of the macrocycle as a whole, but reduces the conjugation of the central cross sub-unit. In conclusion, both criteria can be used confidently for evaluating the aromaticity for the studied systems.

A theoretical approach to the influence of the macrocycle conformation on the molecular electronic structure in Mg-porphyrins

Nonplanar saddled (sad) ruffled (ruf) and domed (dom) conformations of the Mg-porphyrin (MgP) macrocycle in several degrees of deformation have been computed. These symmetrical distortion modes were induced in unsubstituted macrocycle using molecular definitions for calculations which permits us to achieve a systematical variation of the nonplanarity varying only a convenient geometrical parameter of the molecule. Series of nonplanar macrocycles like those synthesized in previous works employing peripheral substitutions are obtained. The procedure here used to induce deformations gives the possibility of investigating the modulator role of the out-of-plane distortions on the geometry and electronic properties of the porphyrin avoiding additional influences due to the substituents or the surrounding protein scaffolding.

Molecular modeling of porphyrin-based conjugates and subphthalocyanine aggregates

A theoretical study was carried out on both porphyrin-based conjugates (with interest in the so-called artificial photosynthesis) and subphthalocyanine aggregates (with potential applications as new materials for optoelectronics, solar energy and other uses). A simple molecular orbital model for studying the role of the spacer groups in the electron transfer in porphyrin-quinone conjugates was developed. The influence of the π-π interaction, hydrogen association and covalent linkage on the stability and structural features in porphyrin-porphyrin complexes as well as the charge separation in donor-acceptor porphyrin dimers, were reproduced. Theoretical models suggest the potential feasibility of SubPcs aggregative processes leading to nanometer-sized fully aromatic fullerene-like molecular architectures.

On the molecular electron structure of three phosphinine‐containing macrocycles

A broad set of structural models and theoretical methods has been successfully used for studying both the molecular electron structure of the silacalix[3]phosphinine and the changes of the macrocycle core under the conditions that frequently correspond to its complexes with metals. The macrocycle core of the silacalix[3]phosphinine and its neutral derivatives are strongly deviated from the main molecular plane. The phosphorous electron lone pairs and the π‐cloud of the phosphinine units give the main contribution to the electron valence structure in the silacalix[3]phosphinine and also in its both oxidized and reduced derivatives. Although the electron lone pairs of the P atoms tend to be strongly repulsive, they are either totally or partially extended above all the fragment of the phosphorous atoms depending on geometrical factors or even strongly coupled with the π‐cloud of the phosphinine units. Electronic processes that take away part of the electron density from the macrocyle favor both its planar configuration and the asymmetric distribution of the valence electrons in the silacalix[3]phosphinine and its derivatives. The limit condition to this effect is the appearance of a new in‐plane σ molecular orbital between the P atoms of two neighboring phosphinine units.