Aggregation behavior in unsymmetrically substituted metal-free phthalocyanines

Phthalocyanines (Pcs) generally have a strong tendency for stacking in solution to form dimer and high order oligomers owing to the π-π, metal-ligand coordination, hydrogen bonding and donor-acceptor interactions between planar rings. Large substituents in peripheral positions, solvents and their amount and the central metal affect the aggregation to a remarkable extent. In Pcs, aggregation results in lowering the solubility, bringing purification and characterization problems and decreasing the photosensitizing efficiency. The aim of this study is to determine the predominant reasons inhibiting the aggregation in an unsymmetrically substituted metal-free Pc which contains three naphthoxy units and one carboxy-1,2-dioxyphenyl in THF. Dispersion-corrected density functional theory interaction energy calculations performed at B97-D/TZVP level revealed that aggregation in these complexes are prevented due to the strong solvent-phthalocyanine interactions rather than the existence of large substituents.