Novel Organic–Inorganic Hybrid Cu(I)-Based Metal Halides: Anti-Thermal Quenching, Interconvertible Structure and Encryption Application

Controllable structural switching and suppressed thermal quenching remain major challenges for luminescent metal halides. Herein, we report two novel interconvertible zero-dimensional (0D) Cu(I)-based hybrid halides, green-emitting (5-CTPP)CuBr₂ and orange-emitting (5-CTPP)₂Cu₄Br₆ (5-CTPP = (5-carboxypentyl)triphenylphosphonium, C₂₄H₂₆BrO₂P), synthesized via similar protocols using identical reactants. Both compounds exhibit strong photoluminescence with high quantum yields of 98.0% for (5-CTPP)₂Cu₄Br₆ and 46.3% for (5-CTPP)CuBr₂. Spectroscopic investigations and density functional theory (DFT) calculations confirm that the emissions originate from self-trapped excitons (STEs). Notably, reversible structural transformation between the two phases can be readily triggered by methanol or thermal stimuli, accompanied by a dynamic photoluminescence color switch. Remarkably, both compounds display pronounced anti-thermal quenching (ATQ) behavior within a specific temperature range, attributed to the thermal detrapping of excitons from shallow defect states. The combination of facile and controllable phase interconversion with distinctly separated excitation spectra highlights their promising potential for room-temperature anti-counterfeiting and encryption applications.