Two-phase Couette flow linear dichroism measurement of the shear-forced orientation of a palladium(ii)-induced aggregate of thioether-derivatised subphthalocyanines at the toluene/glycerol interface

Abstract

Formation of the Pd(II)-induced thioether-derivatised subphthalocyanine Subpc(SR)₆6 (R = Et (ethyl) or Bz (benzyl)) aggregate at the toluene/glycerol interface was investigated by means of a new in situ spectrophotometric method using two-phase Couette flow (TPCF). The shear-forced orientation of the aggregate of Subpc(SR)₆6–Pd(II) complexes formed at the toluene/glycerol interface was studied by their linear dichroism (LD) spectra. The H-aggregate of the Subpc(SEt)₆6–Pd(II) complex gave no LD signal, but the J-aggregate of the Subpc(SBz)₆6–Pd(II) complex clearly afforded LD spectra at a wide range of rotation speeds, suggesting a longer J-aggregate structure in the Subpc(SBz)₆6–Pd(II) system. The relaxation kinetics of the shear-forced orientation of the Pd(II)–Subpc(SBz)₆6 aggregate were observed after stopping the rotation and analysing using a multi-exponential decay equation. By increasing the Subpc(SBz)₆6 concentration in toluene, the fast relaxation fraction of 6.6–7.5 seconds decreased and the slow relaxation fraction of 292–322 seconds increased. The results obtained in this study demonstrate that the TPCF method is useful for studying the size distribution of aggregates formed at liquid/liquid interfaces.