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Haoran Lin1 Chenkun Zhou1 Yu Tian1 Tiglet Besara1 Jennifer Neu1 Theo Siegrist1 Yan Zhou1 James Bullock2 Kirk Schanze2 Wenmei Ming3 Mao-hua Du3 Biwu Ma1

1, Florida State University, Tallahassee, Florida, United States
2, University of Florida, Gainesville, Florida, United States
3, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

Multiple types of organic metal halide hybrid materials have been explored in our group over the past few years. The structures of these organic metal halides range from three-dimensional (3D) to zero-dimensional (0D) classified by the connection method of the metal halide units. And this time we have discovered a single crystalline material that contains large arrays of one-dimensional (1D) metal halide nanotubes surrounded by organic ligands.
The single crystalline bulk assembly of organic metal halide nanotubes possess a chemical formula of (C6H13N4)3Pb2Br7. In the nanotube structure, six face-sharing metal halide dimers (Pb2Br95-) connect in corners to form rings that extend in one dimension, of which the inside and outside surfaces are coated with protonated hexamethylenetetramine (HMTA) cations (C6H13N4+). The individual nanotubes further assemble to bulk crystals in the form of hexagonal close compact. Since the nanotubes have minimum interaction with each other, the bulk quantum material could exhibit the intrinsic properties of an individual organic metal halide nanotube. Computational and experimental results show that this unique 1D tubular structure possesses highly localized electronic states with strong quantum confinement, resulting in the formation of self-trapped excitons that give strongly Stokes shifted broadband yellowish-white emission with photoluminescence quantum efficiency (PLQE) of ~ 7 %. Other than the application in the field of solid state lighting, this functional nanotube could have many potential applications in catalysis, gas storage, electronic devices, molecular machines, etc.
Having realized single crystalline bulk assemblies of two-dimensional (2D) wells, 1D wires, and now 1D tubes using organic metal halide hybrids, our work significantly advances the research on bulk assemblies of quantum-confined materials. The excitement of this work lies not only in the specific achievements, but also in what it represents in terms of new opportunities of organic metal halide hybrids with structures beyond conventional perovskites.

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