Synthesis of novel phthalocyanine-tetrathiafulvalene hybrids; intramolecular fluorescence quenching related to molecular geometry

A number of silicon phthalocyanine bis-esters have been synthesized and characterized, with axial ligands containing one or more tetrathiafulvalene groups. Variations in the substitution positions around a central aromatic "hinge" within the ligands lead to different molecular geometries, and the fluorescence of the macrocyclic core is subsequently quenched to varying degrees by the electron-rich tetrathiafulvalene moiety, the magnitude of this effect being dependent upon both the relative separation of the two units and the flexibility of the linking group. Pc derivative 24, with a highly flexible linker group, and pc derivative 28, with a dendritic axial ligand, have the intensity of the macrocycle emission reduced by 99% and 96%, respectively, relative to a similar silicon pc reference compound lacking the TTF moieties. Molecular modeling studies of a series of such hybrids allow the degree of this fluorescence quenching to be related to the intramolecular spacing. Additionally, the potential for rapid electrochemical switching of the phthalocyanine fluorescence by oxidation of the appended tetrathiafulvalene units is explored.