Phase Engineering for Achieving Full-Color Tunable Emission from Blue to Red and Multi-Level Information Security in Isomeric Hybrid Copper Halides

The design and synthesis of novel hybrid metal halides polymorphs with full-color tunable emission are critical for the advancement of solid-state lighting and display technologies. However, it remains challenging and rarely reported. Herein, we successfully synthesized three new zero-dimensional (0D) hybrid isomeric copper (I) halides, namely α-/β-/γ-(BuPh₃P)₂Cu₂I₄ (where BuPh₃P⁺ = butyltriphenylphosphonium, C₂₂H₂₄P⁺), featuring the same edge-sharing [Cu₂I₄]²⁻ units. Notably, the monoclinic α-(BuPh₃P)₂Cu₂I₄ and β-(BuPh₃P)₂Cu₂I₄, both belonging to the P2₁/n space group, exhibit bright blue and orange emission, respectively. The orthorhombic-phase γ-(BuPh₃P)₂Cu₂I₄ with space group Pbca and larger lattice volume shows vivid red emission, thus achieving tunable full-color emission wavelength spanning from blue (445 nm) to red (667 nm), representing the first instance of such broad tunability through adjusting the spatial arrangement of the organic and inorganic parts. Interestingly, α-(BuPh₃P)₂Cu₂I₄ undergoes a reversible photo-induced fluorochromism, transitioning from blue to green. Furthermore, a reversible phase transformation between α- and β-(BuPh₃P)₂Cu₂I₄ can be triggered by dichloromethane and ethyl acetate. As such, a photo-responsive switchable system and a multistage information encryption/decryption system are successfully devised through leveraging unique multi-stimuli-responsive properties.