Tunable Dimensionality and Emission of Organic Metal Halides by Denser Stacking of Pb–Br Polyhedra

Organic metal halides (OMHs) have attracted extensive
research
interests due to their interesting photoluminescent properties. However,
to date, most OMHs have been synthesized through the trial-and-error
method, and it remains a big challenge to control the molecular-level
structures through directed synthetic approaches to rationally optimize
luminescence properties. In this work, we proposed a crystal structure
modulation strategy to control the dimensionality and optical properties
of OMHs by increasing the packing density of Pb–Br octahedra
via altering the precursor stoichiometry. By precisely adjusting the
ratio of 3-aminomethylpyridine to PbBr2 in the initial
reactants, (C6N2H10)2PbBr6 (0D-J1) with a 0D structure, (C6N2H10)­PbBr6 (2D-J2) with a 2D structure, and C3NH5PbBr (3D-J3) with a 3D structure were successfully
synthesized. 0D-J1 exhibits a bright broadband yellow emission with
a photoluminescence quantum yield (PLQY) of 35.40%. 2D-J2 shows a
free exciton narrowband emission at room temperature and self-trapped
excitons (STEs) emission at low temperatures. 3D-J3 displays a permanent
defect state broad emission at room temperature. Additionally, the
synthesis of compounds from the T series and P series with different
dimensionalities further verifies the general applicability of this
strategy. This strategy enables the directed control of the structure
and optical properties of LD-OMHs while preserving the functionality
of organic cations, and paves an avenue for designing and synthesizing
LD-OMHs with functional coordination between organic cations and inorganic
polyhedra. Together with the efficient emission and outstanding stability
of 0D-J1, a high-performance white-light emitting diode (WLED) with
a high color rendering index (CRI) of 92 is demonstrated.