Reversible phase-transformation-induced thermal quenching in Mn(II) chlorides for high-precision information encryption and thermal energy storage

Photoluminescent materials are widely used in information security applications, yet high-precision optical information encryption remains difficult to achieve. Here we report two monoclinic zero-dimensional organic–inorganic hybrid Mn(II) chloride crystals (C19H42N)2MnCl4 and (C21H46N)2MnCl4. Both show green emission with photoluminescence quantum yields of 85.7% and 89.3%. Upon heating, photoluminescence (PL) is quenched abruptly at 333 and 343 K (ΔT = 10 K) and recovers upon cooling, driven by reversible order–disorder solid–solid phase transitions with phase-transition enthalpies of 140.6 and 160.3 J g–1, respectively. Using two closely spaced PL quenching temperatures, we demonstrate a temperature-window encryption scheme for optical information encryption and anti-counterfeiting, where correct information is revealed only within 333 ≤ T < 343 K. Furthermore, combining latent-heat storage with a temperature-gated PL ON/OFF readout provides a straightforward route to visualized thermal energy storage. This work reveals phase-transition-induced PL quenching and its applications in optical information encryption and visualized thermal energy storage, providing a strategy for designing multifunctional thermo-responsive luminescent materials. Photoluminescent materials are widely used in information security applications, yet high-precision optical information encryption remains difficult to achieve. Here the authors report two monoclinic zero-dimensional organic–inorganic hybrid Mn(II) chloride crystals and characterize their phase-transition-induced photoluminescence quenching.