Targeted Synthesis of Trimeric Organic–Bromoplumbate Hybrids That Display Intrinsic, Highly Stokes-Shifted, Broadband Emission

Abstract

Zero-dimensional (0D) hybrid organic-inorganic lead halides have been shown to display efficient broadband photoluminescence and are, therefore, of significant interest for artificial lighting applications. However, work that investigates the formability of the materials as a function of templating organic cation structure are rare. This severely limits our ability to rationally design new materials displaying specific structural and photophysical properties. With the goal of accessing rare 0D trimeric bromoplumbates, we have systematically varied templating N-alkylpyridinium cations and examined their impact upon inorganic lattice structure. Whereas comparatively short and flexible N-alkyl substituents (ethyl, 2-hydroxyethyl, and pentyl) yield one-dimensional (1D) inorganic chains, more rigid substituents (benzyl, acetamidyl, and cyanomethyl) afford hybrids composed of lead-bromide face-sharing trimers ([Pb3Br12]6-). Of the rigid substituents studied, benzyl groups were found to enforce the highest level of distortion of the [PbBr6]4-octahedra that comprise their trimeric structures. Upon exposure to ultra-violet (UV) light, N-benzylpyridinium lead-bromide (1)6[Pb3Br12] exhibits a broadband emission, centered at 571 nm, which spans from 400 to 800 nm. More specifically, it displays a large Stokes shift of ca. 1.39 eV and a full width at half maximum (FWHM) of ca. 146 nm. This broadband emission decays with a comparatively long lifetime of 426 ns at room temperature, which increases to 5.8 µs at 77 K. The reduced size and dimensionality of its inorganic lattice also results in a photoluminescence quantum yield (at least 10 %) that is approximately one order magnitude higher than that of its 1D congeners. Mechanistically, broadband emission in (1)6[Pb3Br12] is believed to originate from triplet excited state(s) obtained from excited-state structural reorganization of the [Pb3Br12]6-moiety.

Large Cation Engineering in Two-Dimensional Silver–Bismuth Bromide Double Perovskites

“…60 Similar emissions from self-trapped carriers have been reported for 2D lead halide perovskites and other corrugated metal−halide complexes. 61,62 On the other hand, the emission at 2.6 eV can be assigned to the band-to-band exciton recombination or to STH emission, where only the hole undergoes localization. In Figure 7, we summarize the photophysics of BA and iBA-based model systems, and the assignment discussed above.…”

Recent Advances in Luminescent Zero‐Dimensional Organic Metal Halide Hybrids

“…Meanwhile, by systematically varying templating N‐alkylpyridinium cations, Febrainsyah and coworkers have developed distinct trimeric bromoplumbate architectures (Figure 4e). [ 72 ] Detail studies of the optical properties were performed on (benzyl) 6 [Pb 3 Br 12 ] and it was found that (benzyl) 6 [Pb 3 Br 12 ] exhibits a large Stokes shifted broadband emission, which is more efficient than those of its 1D analogs. Despite these recent achievements on 0D organic–inorganic hybrids containing metal halide clusters, fundamental understanding of the structural‐property relationships for this class of materials is still limited, and rational synthetic control of the size and geometry of metal halide clusters has not yet been well established.…”

“…(bottom) View of single crystal structure of (benzyl) 6 [Pb 3 Br 12 ] and their room temperature UV-vis DRS and PL spectra. Reproduced with permission [72]. Copyright 2020, American Chemical Society.…”

The classification of 1D `perovskites'

“…In a search through the CSD for only Pb-Br-and Pb-I-based structures, around 190 unique compounds were found to take on this connectivity. Some well-known examples include 1-ethylpyridin-1-ium bromide (Febriansyah et al, 2020), 1-benzylpyridin-1-ium iodide (Febriansyah et al, 2020) and imidazolium lead iodide (Arora et al, 2019).…”

“…With the rising number of reported 1D hybrid perovskite structures, there has been a wide variety of names given to these structures, ranging from 'one-dimensional perovskite' (Yuan et al, 2017;Seth et al, 2019), 'zigzag edge-sharing perovskite' (Jung, 2020), 'double-chain one-dimensional perovskite' (Jodlowski et al, 2016), 'face-sharing polytype' (Stoumpos et al, 2017), 'plumbate chains' (Febriansyah et al, 2020) to 'perovskitoid' (Stoumpos et al, 2017;Li et al, 2020). For the 3D and 2D perovskite structures, there have been several naming conventions which are widely used for oxide perovskites.…”