(627b) Trap or Triplet? Energy or Electron Transfer? Directing Excited–State Interactions in Perovskite Nanomaterials for Photocatalysis

Transport of energy within light harvesting assemblies is typically carried out with separately synthesized donor and acceptor species, which are then brought together to induce an interaction. Recently, two-dimensional (2D) lead halide perovskites have gained interest for their ability to accommodate and assemble chromophoric molecules within their lattice, creating hybrid organic-inorganic compositions. Using a combination of steady-state and time-resolved absorption and emission spectroscopies, we have now succeeded in establishing the competition between energy transfer and charge trapping in 2D halide perovskite colloids containing naphthalene-derived cations (i.e. NEA2PbX4 where NEA = naphthylethylamine). The presence of room-temperature triplet emission from the naphthalene moiety depends on the ratio of bromide to iodide in the lead halide sublattice (i.e. x in NEA2Pb(Br1-xIx)4), with only bromide-rich compositions showing sensitized emission. Photoluminescence lifetime measurements of the sensitized naphthalene reveal the formation of the naphthalene triplet excimer at room temperature, with an ultrafast rate of formation (roughly 10^9 s-1). At low temperatures (77 K) a new broad emission feature arising from trap states is observed in all samples ranging from pure bromide to pure iodide composition. These results reveal the interplay between sensitized triplet energy transfer and charge trapping in 2D lead halide perovskites, highlighting the need to carefully parse contributions from competing de-excitation pathways for photocatalytic applications.