Partially reversible photochromic behavior of organic-inorganic perovskites with copper(II) chloride

We report that the ultraviolet (UV) light induced photochromic behavior of layered organic-inorganic perovskite material of (C4H9NH3)(2)CuCl4, changed from yellow to brown after irradiation with UV light (10 mW/cm(2)) and partially recovered through storage in the dark. (C4H9NH3)(2)CuCl4 exhibited two distinct absorption bands centered at 286 nm (band I) and 384 nm (band II), which were attributed to the photo-induced exciton formed in 2D inorganic layers sandwiched by organic layers. The blue shift of band I from 287 to 269 nm as well as the decrease of the intensity of band I and band II could be found when samples were irradiated under UV light for different length of time. The simultaneous weakening of the intensity of the N-Ha <-Cl hydrogen bond as well as the vibration of the long Cu-Cl bond in the distorted CuCl6 (4-) octahedron could be detected from the Fourier transform infrared (FTIR) spectra, which resulted the change of charge distribution of the dissymmetric Cl-Cua <-Cl bond and the resulting photochromic behavior.