Direct Investigation of the Reorientational Dynamics of A-site Cations in 2D Organic-Inorganic Hybrid Perovskite by Solid-State NMR

Abstract The reorientational dynamics of A-site cations in organic-inorganic hybrid perovskites (OIHPs) play a pivotal role in determining the physical properties of OIHPs. The nuclear magnetic resonance (NMR) relaxation method is a powerful tool for studying molecular dynamics. However, it faces a significant challenge when applied to measure two-dimensional (2D) OIHPs, where the small signals of A-site cations overlap with the much larger signals of the organic spacers. Here, we demonstrate a novel strategy to tackle the spectral overlapping problem while investigating the dynamics of A-site cations by using rotational-echo double resonance (REDOR) NMR combined with the synthesis of 2D OIHPs, consisting of isotopically enriched A-site cations of 13C-methyl-15N-ammonium, [U-13C,U-15N]MA. The direct investigation of the reorientational dynamics of MA allows us to unveil the interplay between the A-site cation dynamics and the structural rigidity of the organic spacers, so providing a molecular-level insight into the design of 2D OIHPs.