Charge-Transfer Dynamics between Cesium Lead Halide Perovskite Nanocrystals and Surface-Anchored Naphthalimide Acceptors
Meng Li, Silvano R. Valandro, Ru He, Yan Zhao, Ping Yang, Kirk S. Schanze
Abstract
A series of 1,8-naphthalimide (NI) electron acceptors with a primary amine functional group linked to the N-position of the imide by −(CH2)n– linkers with varying lengths are found to quench the photoluminescence (PL) of CsPbBr3 nanocrystals (NC). Three NI-based quenchers were explored, NI-1, NI-2, and NI-3, with n = 2, 8, and 12, respectively. The PL quenching is attributed to photoinduced electron transfer from the exciton state of the CsPbBr3 NCs to the naphthylimide acceptor. An NI acceptor that lacks the NH2 group does not quench the PL, which reveals that the amino group serves to anchor the acceptors to the surface of the NC. The photoinduced charge-transfer mechanism is supported by picosecond transient absorption (TA), which finds a long-lifetime bleach (>7 ns) for the CsPbBr3 NCs with surface-anchored NI-1 acceptors. Steady-state and time-resolved PL quenching was subjected to Stern–Volmer (SV) analysis. The results show that the quenching efficiency varies in the order NI-1 ≫ NI-2 > NI-3, with KSV ranging from ∼106 M–1 for NI-1 to ∼105 M–1 for NI-3. The quenching efficiency is approximately the same for steady-state and dynamic quenching. The results are interpreted by a mechanism where the exciton quenching dynamics is controlled by the rate of interfacial electron transfer. Diffusion and/or detrapping of the CsPbBr3 exciton may also play a role in determining the rate of quenching.