Two-Dimensional Lead Halide Perovskites Templated by a Conjugated Asymmetric Diammonium

We report novel two-dimensional lead halide perovskite structures templated by a unique conjugated aromatic dication, N,N-dimethylphenylene-p-diammonium (DPDA). The asymmetrically substituted primary and tertiary ammoniums in DPDA facilitate the formation of two-dimensional network (2DN) perovskite structures incorporating a conjugated dication between the PbX42– (X = Br, I) layers. These 2DN structures of (DPDA)PbI4 and (DPDA)PbBr4 were characterized by single-crystal X-ray diffraction, showing uniquely low distortions in the Pb–X–Pb bond angle for 2D perovskites. The Pb–I–Pb bond angle is very close to ideal (180°) for a 2DN lead iodide perovskite, which can be attributed to the ability of the rigid diammonium DPDA to insert into the PbX62– octahedral pockets. Optical characterization of (DPDA)PbI4 shows an excitonic absorption peak at 2.29 eV (541 nm), which is red-shifted in comparison to similar 2DN lead iodide structures. Temperature-dependent photoluminescence of both compounds reveals both a self-...