Coronenetetraimide-centered cruciform pentamers containing multiporphyrin units: synthesis and sequential photoinduced energy- and electron-transfer dynamics.

Abstract

A series of coronenetetraimide (CorTIm)-centered cruciform pentamers containing multiporphyrin units, in which four porphyrin units are covalently linked to a CorTIm core through benzyl linkages, were designed and synthesized to investigate their structural, spectroscopic, and electrochemical properties as well as photoinduced electron- and energy-transfer dynamics. These systems afforded the first synthetic case of coroneneimide derivatives covalently linked with dye molecules. The steady-state absorption and electrochemical results indicate that a CorTIm and four porphyrin units were successfully characterized by the corresponding reference monomers. In contrast, the steady-state fluorescence measurements demonstrated that strong fluorescence quenching relative to the corresponding monomer units was observed in these pentamers. Nanosecond laser flash photolysis measurements revealed the occurrence of intermolecular electron transfer from triplet excited state of zinc porphyrins to CorTIm. Femtosecond laser-induced transient absorption measurements for excitation of the CorTIm unit clearly demonstrate the sequential photoinduced energy and electron transfer between CorTIm and porphyrins, that is, occurrence of the initial energy transfer from CorTIm (energy donor) to porphyrins (energy acceptor) and subsequent electron transfer from porphyrins (electron donor) to CorTIm (electron acceptor) in these pentamers, whereas only the electron-transfer process from porphyrins to CorTIm was observed when we mainly excite porphyrin units. Finally, construction of high-order supramolecular patterning of these pentamers was performed by utilizing self-assembly and physical dewetting during the evaporation of solvent.