Interfacial aggregation of thioether-substituted phthalocyaninatomagnesium(ii)–palladium(ii) complexes in the toluene/water system

Abstract

The interfacial aggregation of three thioether-substituted phthalocyanine–magnesium(II) complexes, MgPc(SR)₈, of (2,3,9,10,16,17,23,24-octakis-ethylthiophthalocyaninato)magnesium(II), [MgPc(SEt)₈], (2,3,9,10,16,17,23,24-octakis-benzylthiophthalocyaninato)magnesium(II), [MgPc(SBz)₈], and (2,3,9,10,16,17,23,24-octakis-benzhydrylthiophthalocyaninato)magnesium(II), [MgPc(SBh)₈] were investigated in the toluene/water system by means of a centrifugal liquid membrane (CLM) method. Aggregation of MgPc(SR)₈ molecules at the interface was significantly promoted by the complexation with soft metal ions such as Pd(II) and Hg(II) added to the aqueous phase. The interfacial adsorption of MgPc(SEt)₈ was caused even in the absence of Pd(II) by the formation of a co-facial H-dimer, but the presence of Pd(II) promoted H-dimer aggregation at the interface. In the cases of MgPc(SBz)₈ and MgPc(SBh)₈, there was observed no significant self-aggregation, but in the presence of Pd(II), the interfacial aggregation of Pd(II) complexes of MgPc(SBz)₈ and MgPc(SBh)₈ proceeded remarkably. It was suggested that MgPc(SBz)₈–Pd(II) and MgPc(SBh)₈–Pd(II) could not form H-aggregates, because of the steric hindrance of benzyl or bezhydryl group, but they formed J-aggregates. Furthermore, MALDI-TOF/MS spectra indicated that oligomers of MgPc(SBz)₈–Pd(II) complex were formed at the liquid/liquid interface. The present study demonstrated the first example of Pd(II)-induced interfacial aggregation of phthalocyanine derivatives at the liquid/liquid interface, and suggested the possibility of controlling the aggregate structure between H- and J-aggregates by the size of peripheral substitute groups.