Adsorption equilibria of novel phthalocyaninatomagnesium(II) derivatives with thioethers at the toluene/water interface

Three novel phthalocyaninatomagnesium(II) derivatives with eight peripheral thioethers (MgPc(SR)(8)) such as (2,3,9,1 0,16,17,23,24-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-benzhydrylthiophthalo-cyaninato)magnesium(II) (MgPc(SBh)(8)) were synthesized. The interfacial adsorption and aggregation behavior of the three derivatives in a toluene/water system were examined by means of a high-speed stirring (HSS) method and a centrifugal liquid membrane (CLM) method. The interfacial adsorption constant of each MgPc(SR)(8) derivative at the toluene/water interface was determined by the HSS measurement. Only in the case of MgPc(SEt)(8), the formation of the trimer was observed at the interface. Moreover, the CLM measurements showed that the interfacial aggregate of MgPc(SEt)(8) had a new broad band (613 nm) at the blue flank of the Q band (702 nm) of MgPc(SEt)(8) monomer, which might be ascribed to H-aggregate. Extended double-dipole (EDD) model calculations suggested a cofacially stacked arrangement of MgPc(SEt)(8) molecules in the trimer. The interfacial spectral change indicated that the aggregation of MgPc(SEt)(8) at the toluene/water interface proceeded in a two-step, three-stage (monomer --> dimer --> trimer) formation.