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

Abstract 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‐(BuPh 3 P) 2 Cu 2 I 4 (where BuPh 3 P + = butyltriphenylphosphonium, C 22 H 24 P + ), featuring the same edge‐sharing [Cu 2 I 4 ] 2− units. Notably, the monoclinic α‐(BuPh 3 P) 2 Cu 2 I 4 and β‐(BuPh 3 P) 2 Cu 2 I 4 , both belonging to the P 2 1 / n space group, exhibit bright blue and orange emission, respectively. The orthorhombic‐phase γ‐(BuPh 3 P) 2 Cu 2 I 4 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‐(BuPh 3 P) 2 Cu 2 I 4 undergoes a reversible photo‐induced fluorochromism, transitioning from blue to green. Furthermore, a reversible phase transformation between α‐ and β‐(BuPh 3 P) 2 Cu 2 I 4 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.