Excitation Energy Transfer by Electron Exchange via Two-Step Electron Transfer between a Single-Walled Carbon Nanotube and Encapsulated Magnesium Porphyrin

Because of the strong photoabsorption of porphyrin and its derivatives in the visible light region, composites of porphyrin–carbon nanotubes show promise as materials for photovoltaic and photoenergy transfer applications. Studies have reported the photoexcited states of functionalized carbon nanotube composites containing externally attached porphyrin. However, the photoexcited states of carbon nanotube composites containing encapsulated porphyrin moieties have not been investigated. The enhancement of photostability and chemical stability of porphyrins, which is crucial in device applications, is expected in these composites. In this study, we fabricated a composite of single-walled carbon nanotubes and encapsulated porphyrins to investigate ultrafast relaxation dynamics of photoexcited states by steady-state measurements and femtosecond time-resolved measurements. We found that excitation energy transfer by electron exchange via two-step electron transfer between the encapsulated porphyrin and single-walled carbon nanotube occurs in the femtosecond regime. This study provides an insight into photovoltaic functionality and photoenergy transfer in molecule-encapsulating materials.