Thermochromic Phase Transitions of Long Odd-Chained Inorganic-Organic Layered Perovskite-Type Hybrids [(CnH2n+1NH3)2PbI4], n=11, 13, and 15

We investigate the last members of a series of inorganic-organic hybrid materials of the general formula[(CnH2n+1NH3)2PbI4] (abbreviated CnPbI). The self-assembly of the inorganic and organic components has a perovskite-likestructure as the two-dimensional (2D) inorganic layers have four corners of the lead(II) iodide octahedra being shared out. Theinorganic layers are separated by bilayers of alkylammonium chains, in this case withn= 11, 13, and 15. These materials exhibitcomplex phase behavior in the temperature range from-20 to + 81 degrees C. Differential scanning calorimetry and single-crystal X-raydiffraction enabled the phase transition temperatures and enthalpies to be determined and the structural changes that occur at thephase transition temperature. The number of phases is dependent on the chain length: forn= 11 and 15, there are three phases, andforn= 13, there are four phases. Regardless of the number of phases, all three compounds have identical lowest-temperature phases(all stable below room temperature), which have inorganic layers that are staggered, alkylammonium chains that are planar andnonplanar, and yellow crystals. The room-temperature phases for the three compounds differ, but all are orange. C11PbI hasstaggered layers, and C13PbI and C15PbI have identical room-temperature phases with eclipsed layers. C13PbI and C15PbI also showan additional phase between the lowest-temperature and room-temperature phases.

Automated summary

In this study, we investigated a series of inorganic-organic hybrid materials (CnPbI) and found that they exhibit complex phase behavior and different phase structures, with the chain length playing a role. Regardless of the number of phases, all three compounds have the same lowest-temperature phase, but different room-temperature phases.