Monocation vs Dication 2D → 1D Dimensional Reduction Agent Affording Broad Band Emitters 1D Lead Bromide Perovskites

The synthesis, crystal structures, and optical properties of the 2D perovskite (Cyst)PbBr4 (1) and two 1D perovskite hybrids Cs(Cyst)PbBr5 (2) and (Cyst)2PbBr5,Br (3) based on the cystaminium dication (Cyst2+) exhibiting a helical chiral conformation are described in this work. The 1D compounds can be conceptually described from the 2D mother structure by the dimensional reduction concept. Thus, the addition of one CsBr unit to one (Cyst)PbBr4 leads to Cs(Cyst)PbBr5 (2), whose structure can be described as organic-inorganic sheets [(Cyst)PbBr5]− separated by Cs+ monocation in the intersheet space, while the addition of one (Cyst),2Br unit to one (Cyst)PbBr4 leads to (Cyst)2PbBr5,Br (3) whose structure can be described as organic-inorganic sheets [(Cyst)PbBr5]− separated by Cyst2+ dications and free bromides in the intersheet space. The acentric compound (2) crystallizing in the P21 space group exhibits SHG properties, while the three compounds emit light when excited in the UV-visible domain. The 2D compound exhibits two close excitonic narrow peaks in the blue region, certainly resulting from bulk and edge states as already observed. In contrast, the lower-dimensional compounds (2) and (3) have a broad band emission type covering a good part of the visible range, illustrating the interest of such low-dimensional 1D compounds compared to 2D mother compounds for white light type emission.