Synthesis and Photosensitizing Properties of an Activatable Phthalocyanine-Subphthalocyanine Triad

In this article, we describe a photosensitizer (PS) whose ability to generate singlet oxygen (1O2) and fluorescence emission has been designed as tumor responsive. More specifically, the PS consists of a silicon phthalocyanine (SiPc) core, axially substituted with two subphthalocyanine (SubPc) units, covalently linked by a disulfide linker, which is cleavable in the presence of a strong reducing agent. Initially, the SubPc units quench the SiPc fluorescent and 1O2-generating properties, most probably by electronic energy transfer. Upon entering a reducing environment, e.g., like those in tumor cells, the disulfide linker would be cleaved and the quenching would be undone, resulting in a sudden generation of 1O2 and a strong fluorescence of both the SiPc and SubPc units. Herein, this behavior has been probed in solution by means of using DTT as the reducing agent that induces the PS activation.