LAUSR

We utilized two organic dications containing, respectively, a pyridinium and an imidazolium core to construct new n = 1 (where n refers to the number of contiguous two-dimensional (2D) inorganic layers, i.e., not separated by organic cations) 2D lead–iodide perovskites 1 and 2. The former material exhibits a (100)- and the latter a very rare 3 × 3 (110)-structural type. Compared with primary ammonium functionality, their constituent ring-centered positive charges have lower charge density. As a result, [PbI6]4– interoctahedral distortions of the inorganic lattice in 1 and 2 are reduced (Pb–I–Pb bond angles are as high as 166° and 174°, respectively). This results in bathochromically shifted optical features. In addition, the compact nature of the dications produces extremely short lead–iodide sheet separations, with respective iodide–iodide (I···I) distances as small as 4.149 and 4.278 A. These are among the shortest separations of adjacent lead–iodide layers ever reported for such materials. When crystal...