Tug-of-War at the Interface: Electron Transfer in Ni-Doped CsPbBr ₃ –Fluorophore Hybrid with Methyl Viologen

Resolving the time scales of energy and charge transfer processes in light harvesting systems is pivotal to the advancement of artificial photosynthesis and next-generation optoelectronic devices. Herein, we present a detailed time-resolved investigation of a light-harvesting triad composed of Ni-doped CsPbBr 3 perovskite nanocrystals (Ni:PNCs), rhodamine B (RhB), and methyl viologen (MV 2+ ). This triad is strategically selected for establishing a sequential relay mechanism-Förster resonance energy transfer coupled with photoinduced electron transfer. Ni 2+ doping imparts enhanced structural rigidity resulted in improved ethanol tolerance of the PNCs. An energy transfer efficiency of ∼88% from Ni:PNC to RhB demonstrates a highly efficient energy transfer process. MV 2+ binds to Ni:PNC with an apparent association constant of ∼10 6 M –1, nearly an order of magnitude higher than that of RhB (∼10 5 M –1 ), confirming its preferential surface interaction. Nonlinear photoluminescence quenching behavior of Ni:PNC with MV 2+ has been elucidated with Perrin Formalism. A nearly 2-fold reduction in the Stern–Volmer quenching constant for the Ni:PNC–RhB hybrid compared to pristine Ni:PNC highlights the role of RhB. Femtosecond transient absorption spectroscopy reveals ultrafast electron transfer from the photoexcited Ni:PNC–RhB complex to MV 2+, leading to the formation of MV +• radical species. The rate of energy transfer and rate of electron transfer for Ni:PNC–RhB with MV 2+ are measured to be 1.7 × 10 9 s –1 and 1.7 × 10 10 s –1, respectively. These results provide mechanistic insights into energy-transfer-coupled electron transfer dynamics and place the Ni:PNC-based triad as a promising candidate for solar fuel conversion processes.