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 CsPbBr3-Rhodamine B (RhB) hybrid assembly. PL studies reveal quenching of the CsPbBr3 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 CsPbBr3 by alloying with chloride. This allowed us to tune the spectral overlap between the donor CsPb(Br1-xClx)3 emission and acceptor RhB absorption. For CsPbBr3-RhB, the rate constant for energy transfer (kET) agrees well with Förster theory, whereas alloying with chloride to produce chloride-rich CsPb(Br1-xClx)3 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.