Moisture-Induced reversible structure conversion of Zero-Dimensional organic cuprous bromide hybrids for multiple photoluminescent anti-Counterfeiting, information encryption and rewritable luminescent paper

With social development and the technology advancement, the demand for high-security photoluminescence (PL) anti-counterfeiting and information encryption materials is increasing constantly. Herein, two organic cuprous bromide hybrids, namely (TPA)CuBr2 and (TPA)2Cu4Br6, with variable coordination geometries were synthesized via a facile solution method. (TPA)CuBr2 shines bright cyan emission with a photoluminescence quantum efficiency (PLQE) of 81 % under 254 nm excitation, while (TPA)2Cu4Br6 exhibits orange emission with a PLQE of 95 % upon 365 nm irradiation. Interestingly, a reversible structural conversion could be triggered by water or heat between (TPA)CuBr2 and (TPA)2Cu4Br6, accompanied by a back-and-forth emission color change between cyan and orange under its respective excitation. The emission mechanism of above two compounds was investigated, and the results show that they stem from self-trapped excitons emission. Such PL color switching under the external stimuli of water, heat and different excitation wavelengths enables us to construct a series of anti-counterfeiting and information encryption scenarios. In addition, the rewritable PL paper based on (TPA)CuBr2 with water as ink is realized. These two compounds not only provide a good way to modulate zero-dimensional Cu(I)-based metal halide with highly efficient emission, but also a new example to develop multifunctional applications by organic–inorganic hybrid metal halides.