Photodynamics at the CdSe Quantum Dot–Perylene Diimide Interface: Unraveling the Excitation Energy and Electron Transfer Pathways

Excitation energy and charge transfer processes in perylene diimide dye–CdSe quantum dot complexes have been studied by femtosecond transient absorption spectroscopy. After excitation of the quantum dots high above the band edge, the electronically excited perylene diimide forms on a timescale similar to the ultrafast quantum dot intraband relaxation. An extraordinarily fast energy transfer time of <300 fs is determined, indicating that the transfer from the hot excitonic state competes with quantum dot intraband relaxation. A much slower kinetic component is attributed to the energy transfer from the quantum dot’s lowest excitonic state to perylene diimide. At high dye–quantum dot ratios, the electronically excited dye generated in the energy transfer reaction is reduced by an electron transfer from the quantum dot ground state. This study demonstrates the potential of the investigated organic–inorganic hybrid for the design of tailor-made energy transfer systems, which can be applied in the emerging field of hot exciton utilization.