Discerning two-dimensional metal halide perovskite moieties using solid-state NMR fingerprints

Low-dimensional perovskites hold great promise for optoelectronic applications, spanning from photovoltaics to photonic platforms. The electronic properties of these soft hybrid semiconductors critically depend on their crystal structure, and the ability to clearly discern the connectivity of the inorganic component and the organic molecular packing is crucial to foster the development of improved materials. In this work, we apply solid-state NMR spectroscopy (ssNMR) to compare two perovskites with different structural motifs: the flat 〈100〉-oriented Ruddlesden-Popper (BA)₂PbI₄ and the corrugated 〈110〉-oriented Dion-Jacobson phase (EDBE)PbI₄, which are flat and corrugated layered perovskites, respectively. Combining experimental characterizations under static and magic angle spinning conditions up to 42 kHz with spin relaxation time measurements and density functional theory (DFT) calculations, we show that ¹³C, ¹⁵N and ²⁰⁷Pb spectroscopies provide distinct spectral fingerprints that are characteristic of the perovskites' different connectivities and allow the identification of their local spatial arrangements. Our work provides a deeper understanding of the ssNMR response of 2D perovskites with different connectivities of their inorganic framework, highlighting its key role as a complementary technique to traditional diffraction-based methods.