Band Gap-Tunable, Chiral Hybrid Metal Halides Displaying Second-Harmonic Generation

The introduction of chirality in lead halide perovskites and related
metal halide materials allows for an expansion of their unique and
useful properties toward nonlinear optics. However, when synthesizing
materials based on less toxic metals antimony and bismuth, the large
variability in the crystal structures of their metalates and their
tendency to form molecular or chain-like anion motifs can be a challenge
when creating tunable materials. Here, we show that using a chiral
amine template, we can synthesize an isomorphous family of compounds
[(R)-1-(4-F)­PEA]4[E2X10] ((R)-1-(4-F)­PEA = (R)-1-(4-fluoro)­phenylethylammonium;
E = Sb and Bi; X = Cl, Br, and I) that combines multiple aspects:
the compounds are not only chiral but also feature a trilayered arrangement
of cations and anions that allows for facile cleavage and exfoliation.
The different combinations of E and X allow for a variation of the
onset of absorption between 3.35 and 2.09 eV. Using femtosecond laser
spectroscopy, we show that our materials allow for efficient second-harmonic
generation. Together with a simple synthesis and good stability, this
makes these materials promising candidates for linear and nonlinear
optical devices.