Harnessing Excited-State Energy Transfer for the Activation of Dark Triplet Excitons and Phosphorescence in Hybrid Organic–Inorganic 2D Perovskite

The present work introduces a hybrid organic–inorganic 2D perovskite, where a rational molecular design strategy enables efficient triplet exciton generation through an excited-state energy transfer process. Upon photoexcitation, a sharp emission peak having a narrow bandwidth is observed at ∼400 nm, reflecting excitonic emission from the perovskite, which subsequently undergoes energy transfer to the energetically aligned triplet state of the organic spacer. The triplet state of the spacer molecule then undergoes radiative intersystem crossing to the ground state, resulting in broad phosphorescence emission at ∼560 nm, having an excited state lifetime of ∼30 ms under an ambient atmosphere. Further, the overlap of the phosphorescence spectra of the organic spacer and delayed luminescence of perovskite provides additional evidence for the proposed excited-state energy transfer mechanism. Collectively, the temperature-dependent photoluminescence, PL excitation, and delayed luminescence studies presented here provide strong evidence of the mechanistic insights into the excited-state dynamics in 2D perovskites.