The Origin of Chiroptical Activity in Chiral Perovskite

Chiral perovskites have been extensively studied as a promising candidate for spintronic- and polarization-based optoelectronic devices due to their unusual spin-related properties such as strong spin-orbit coupling, long spin-life time exceeding 1ns and large Rashba splitting. However, the origin of chiroptical activity in chiral perovskites is still unknown, as the chirality transfer mechanism has been rarely studied. Since the chiral perovskite with the Sohncke chiral space group of <i>P</i>2₁2₁2₁ was reported in 2003, their chiroptical phenomena have been interpreted based on their crystallinity. Although (i) crystallization into a chiral crystal structure induced by chiral organic molecules, (ii) chiral distortion on the surface of chiral perovskite nanoparticles, and (iii) chiral dislocations can provide the explanation of their optical and electronic properties, the electronic interactions between the chiral organic molecules and achiral inorganic framework, should also be considered. Here, we discuss the possibility of the chirality transfer via electronic interaction between the chiral organic molecules and achiral inorganic framework related to the strength and direction of hydrogen bonding. We systematically consider the effect of asymmetric hydrogen bonding and related change in the chiroptical activity of chiral perovskite by inducing the conformational change of stacking order between the two chiral organic molecules. First, through the spatial confined growth of chiral perovskite in anodized aluminum oxide template, we can successfully impose the micro-strain into the lattice of chiral perovskite, resulting in rearrangement of chiral organic molecules. As a results, remarkable chiroptical behavior with different absorption of 2.0 10^-3 and distinct photoluminescence of 6.4 10^-2 for left- and right-handed circularly polarized light was observed in nanoconfined chiral perovskites even at room temperature. Theoretical calculations verify that the chirality transfer phenomena mediated by the asymmetric hydrogen bonding between the chiral organic molecules and achiral inorganic frameworks is critical factor for promoting the chiroptical activity of chiral perovskites. Furthermore, the incorporation of guest molecules into the lattice of chiral perovskite evoke the rearrangement of chiral organic molecules, which also can lead to change in chiroptical activity as well as electrical properties. Through solid-state nuclear magnetic resonance spectroscopic measurements and theoretical calculations, we verify the change in the degree of chiral lattice distortion associated with different electronic interaction between the inorganic framework and guest molecules. Finally, as a preliminary proof-of-concept, a vertical-type circularly-polarized light photodetector based on chiral perovskites was developed, exhibiting an outstanding performance with a distinguishability of 0.27 and responsivity of 0.43 A W^-1. Our findings suggest that electronic interactions between the building blocks should be considered when interpreting the chirality transfer phenomena and designing hybrid materials for future spintronic and polarization-based devices.