Achieving an electron transfer photochromic complex for switchable white-light emission

Rapidly Generated, Ultra-Stable, and Switchable Photoinduced Radicals: A Solid-State Photochromic Paradigm for Reusable Paper Light-Writing

Although photochromic molecules have attracted widespread interest in various fields, solid-state photochromism remains a formidable challenge, owing to the substantial conformational constraints that hinder traditional molecular photoisomerization processes. Benefiting from the significant color change upon radical generation, chemical systems enabling a photoinduced radical (PIR) behavior through photoinduced electron transfer (PET) could be ideal candidates for solid-state photochromism within minimized need of conformational freedom. However, the transient nature of radicals causes a dilemma in this Scheme. Herein, we present a general crystal engineering strategy for rapidly generated (7-s irradiation to saturation) and ultra-stable (lasting 12 weeks) PIRs in the solid state, based on the anti-parallel alignment of para-hydroxyphenyl groups of persulfurated arenes to form a strong non-covalent network for efficient PET and radical stabilization. Using this strategy, a PIR platform was constructed, with a superior photochromic behavior remaining in different solid forms (even in the fully-ground sample) due to their transcendent crystallization ability. On this basis, our compounds can be further processed into reusable papers for light-writing, accompanied by water fumigation for modulating the reversible process. This work provides new insights into addressing solid-state photochromism and can inspire a wide range of optical material design from the switchable radical perspective.

High-efficiency color-tunable ultralong room-temperature phosphorescence from organic-inorganic metal halides via synergistic inter/intramolecular interactions

Materials exhibiting highly efficient, ultralong and multicolor-tunable room-temperature phosphorescence (RTP) are of practical importance for emerging applications. However, these are still very scarce and remain a formidable challenge. Herein, using precise structure design, several novel organic-inorganic metal-halide hybrids with efficient and ultralong RTP have been developed based on an identical organic cation (A). The original organic salt (ACl) exhibits red RTP properties with low phosphorescence efficiency. However, after embedding metals into the organic salt, the changed crystal structure endows the resultant metal-halide hybrids with excellent RTP properties. In particular, A2ZnCl4·H2O exhibits the highest RTP efficiency of up to 56.56% with a long lifetime of up to 159 ms. It is found that multiple inter/intramolecular interactions and the strong heavy-atom effect of the rigid metal-halide hybrids can suppress molecular motion and promote the ISC process, resulting in highly stable and localized triplet excitons followed by highly efficient RTP. More crucially, multicolor-tunable fluorescence and RTP achieved by tuning the metal and halogen endow these materials with wide application prospects in the fields of multilevel information encryption and dynamic optical data storage. The findings promote the development of phosphorescent metal-halide hybrids for potential high-tech applications.