Ligand Structure Directed Dimensionality Reduction (2D →1D) in Lead Bromide Perovskite

Low dimensional (2D, 1D) lead halide
perovskites are currently
attracting huge research interest due to their enabling properties.
Demonstrating synthetic control on the dimensionality/structure of
these perovskites is highly challenging. Dimensionality in these perovskites
is largely dictated by the nature/structure and composition of the
incorporating ligands and the utilized synthetic conditions. Here,
we demonstrate chemical composition based control on reduction of
dimensionality (2D → 1D) for lead bromide perovskite utilizing
2-(2-aminoethyl)­isothiourea dihydrobromide as a common precursor ligand
(Isothio Bromide). Controlling the hydrothermal reaction parameters
(temperature, time) at a fixed precursor ratio affords corner-shared,
contorted 2D sheet perovskite and corner-shared, contorted, chiral
1D chain perovskite. Such dimensionality reduction leads to contrasting
photophysical properties: 1D chain perovskite shows long-lived and
self-trapped broad band emission, whereas 2D perovskite shows short-lived,
band edge emission with a long tail. Mechanistic studies and single
crystal structure analysis reveal the incorporation of the utilized
precursor ligand (Isothio Bromide) in 2D perovskite. Surprisingly,
the 1D perovskite is found to be chiral (P21 space group)
incorporating 2-(2-aminoethyldisulfanyl)­ethanamine and ammonium ions
as the achiral ligands generated in situ due to hydrothermal cleavage
of the precursor (Isothio Bromide) ligand. Such structural and compositional
change of the ligands, which manifests a different hydrogen bonding
network in the resultant perovskite structure, plays a decisive role
in dictating the final molecular formula and dimensionality/structure
of the perovskite which largely controls their photophysical properties.