Abstract: We report that the ultraviolet (UV) light induced photochromic behavior of layered organic-inorganic perovskite material of (C₄H₉NH₃)₂CuCl₄, changed from yellow to brown after irradiation with UV light (10 mW/cm²) and partially recovered through storage in the dark. (C₄H₉NH₃)₂CuCl₄ 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−H···Cl hydrogen bond as well as the vibration of the long Cu−Cl bond in the distorted CuCl₆⁴⁻ octahedron could be detected from the Fourier transform infrared (FTIR) spectra, which resulted the change of charge distribution of the dissymmetric Cl−Cu···Cl bond and the resulting photochromic behavior.

Key words: Photochromic behavior, Perovskite, Organic-inorganic hybrid

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