Peripherally octamethyl zinc(II) phthalocyanines with various axial substituents

Abstract

A series of zinc(II) phthalocyanine complexes peripherally octa-substituted by methyl groups and with axially ligated N-donor ligands, (Zn(Me)8Pc-L, where L is pyridine (4), 3-methylpyridine (5), 3,4-lutidine (6) and 3,5-lutidine (7)), was synthesized. All the Zn(Me)8Pc-L complexes 4–7 were obtained in the crystalline form, suitable for X-ray single crystal analysis. The effect of the peripheral substituents as well as the ligation effect of the axial ligands on the structure were analyzed. In all the here studied zinc(II) phthalocyanine derivatives, the interaction of the metal center with the N atom of the axial ligand results in its displacement by ~ 0.4 Å from the N4-isoindole plane of phthalocyaninate macrocycle that adopts a saucer-shaped form. The X-ray geometry and stereochemistry of the zinc(II) phthalocyanine derivatives were compared with that obtained by DFT methods. Analysis of the Hirshfeld's surface shows a reduction of the π···π interactions with the simultaneous increase of the CH···N, CH···N, H···H and CH··· π interactions in the investigated complexes 4–7. Partial MO energy diagrams and the calculated absorption spectra of the Zn(Me)8Pc-L derivatives 4–7 exhibit a bathochromic shift of the maximum absorption wavelength (λmax) in comparison with the spectrum of Zn(Me)8Pc by about 20 nm. Complexes 4–7 have a strong absorption band in the therapeutic window (600–900 nm) and the HOMO-LUMO energy gap is sufficient to excite the ground state of oxygen and therefore they can be tested as potential photosensitizers for PDT.