Directing Energy Transfer in Halide Perovskite-Chromophore Hybrid Assemblies.

Directing the flow of energy and the nature of the excited states that are produced in nanocrystal-chromophore hybrid assemblies is crucial for realizing their photocatalytic and optoelectronic applications. Using a combination of steady-state and time-resolved absorption and photoluminescence (PL) experiments, we have probed the excited-state interactions in the CsPbBr-Rhodamine B (RhB) hybrid assembly. PL studies reveal quenching of the CsPbBr emission with a concomitant enhancement of the fluorescence of RhB, indicating a singlet-energy-transfer mechanism. Transient absorption spectroscopy shows that this energy transfer occurs on the ∼200 ps time scale. To understand whether the energy transfer occurs through a Förster or Dexter mechanism, we leveraged facile halide-exchange reactions to tune the optical properties of the donor CsPbBr by alloying with chloride. This allowed us to tune the spectral overlap between the donor CsPb(BrCl) emission and acceptor RhB absorption. For CsPbBr-RhB, the rate constant for energy transfer () agrees well with Förster theory, whereas alloying with chloride to produce chloride-rich CsPb(BrCl) favors a Dexter mechanism. These results highlight the importance of optimizing both the donor and acceptor properties to design light-harvesting assemblies that employ energy transfer. The ease of tuning optical properties through halide exchange of the nanocrystal donor provides a unique platform for studying and tailoring excited-state interactions in perovskite-chromophore assemblies.