Halogen substitution effects on optical and electrical properties in 3D molecular perovskites

Both 3D organic-inorganic perovskites (Et3P(CH2)2ClCd(dca)3 (1) and Et3P(CH2)2FCd(dca)3 (2) dca = dicyanamide, N(CN)2-) display two sequentially reversible high-temperature phase transitions and switchable dielectric properties. Through halogen substitution, 1 shows exceptional switching behaviour of second harmonic generation effects and remarkably 2 represents the first above-room-temperature 3D ferroelastic material characterized by two ferroelastic phases.