The solid state molecular motions in Cd-based halides monitored by photoluminescence switching

Abstract

The research on low-dimensional organic-inorganic hybrid metal halide materials is attractive due to their flexible structures and outstanding optoelectronic properties. This paper reports a series of novel (PIP)CdX4 compounds (PIP = protonated piperazine), including (PIP)CdI4 (Cd-I), (PIP)CdI2Cl2 (Cd-ICl) and (PIP)CdI2.4Br1.6 (Cd-IBr). It is notable that PIP·2Cl can diffuse into their structures resulting in a luminescent phase (PIP)CdI4·PIP·2Cl (CdI-P). As a result, the PIP molecular motion can be monitored by the photoluminescence switching leading to the bulk luminescent heterostructure. The photophysical property of CdI-P has been studied using temperature-dependent photoluminescence, photoluminescence excitation, time-resolved photoluminescence spectra, and transient femtosecond transient absorption. We propose that the green emission of CdI-P should be from self-trapped excitons (STEs) radiative recombination, which might be related to the isolated Cl- in the structure through the comparison study with (PIP)CdI4·PIP·2I and density functional theory calculation. The superior water solubility will enhance the processibility of title compounds. Finally, an advanced time-resolved information encryption applications are developed.