Synthesis and spectroscopic properties of phthalocyanine dimers in solution

A soluble dimer of a tetra-(methoxy)-tetra-(octyloxy)-substituted silicon phthalocyanine has been prepared. Optical absorption spectra of the compound in solution showed a pronounced solvatochromism, characterized by a rather sharp peak with maximum at 640 nm in aromatic solvents and a broad absorption band consisting of up to five individual peaks for non-aromatic solutions such as THF or chloroform. Nanosecond transient absorption spectra exhibited a long-lived photoinduced absorption band at 520 nm which can be assigned to triplet absorption. Large quantum yields for intersystem crossing ranging between 30% and 40% were observed. These findings are compared to the results on the monomeric and polymeric compounds and discussed in the framework of exciton coupling.