Pressure driven rotational isomerism in 2D hybrid perovskites

Multilayers consisting of alternating soft and hard layers offer enhanced toughness compared to all-hard structures. However, shear instability usually exists in physically sputtered multilayers because of deformation incompatibility among hard and soft layers. Here, we demonstrate that 2D hybrid organic-inorganic perovskites (HOIP) provide an interesting platform to study the stress-strain behavior of hard and soft layers undulating with molecular scale periodicity. We investigate the phonon vibrations and photoluminescence properties of Ruddlesden-Popper perovskites (RPPs) under compression using a diamond anvil cell. The organic spacer due to C4 alkyl chain in RPP buffers compressive stress by tilting (n = 1 RPP) or step-wise rotational isomerism (n = 2 RPP) during compression, where n is the number of inorganic layers. By examining the pressure threshold of the elastic recovery regime across n = 1-4 RPPs, we obtained molecular insights into the relationship between structure and deformation resistance in hybrid organic-inorganic perovskites.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)Submitted/Accepted versionK.P.L. wishes to acknowledge grant P0043087 of Hong Kong Polytechnic University. T.Y. gratefully acknowledges strong support from the Presidential Postdoctoral Fellowship of Nanyang Technological University. T.Y. and H.S. would like to acknowledge the support from the Singapore National Research Foundation via Competitive Research Programme (NRF-CRP21-2018-0007 and NRF-CRP23-2019-0007). Z.S. and L.Y. would like to acknowledge the MOE Tier 2 MOE-T2EP50220- 0020 and MOE Tier 1 RG57/21 and RG156/19 (S). K.L. would like to acknowledge the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. PolyU15305221 for GRF project funded in 2021/22 Exercise). Y.C. would like to acknowledge the University of Macau (SRG2019-00179-IAPME, MYRG2020-00075-IAPME) and the Science and Technology Development Fund from Macau SAR (FDCT-0163/2019/A3), the Natural Science Foundation of China (Grant 22022309) and Natural Science Foundation of Guangdong Province, China (2021A1515010024). This work was performed in part at the HighPerformance Computing Cluster (HPCC), which is supported by the Information and Communication Technology Office (ICTO) of the University of Macau