Structural Transformation and Photochromism of Chiral Hybrid Metal Halides for Stimulus-Responsive Phosphorescence...

Chiral organic-inorganic hybrid metal halides (OIMHs) have emerged as promising systems for stimuli-responsive circularly polarized luminescence (CPL). However, chiral OIMHs featuring both photochromic CPL and room temperature phosphorescence (RTP) have rarely been reported. Herein, we adopted multi-protonation effect to construct chiral OIMHs using axially chiral bipyridyl molecules (R-L/S-L). Nonprotonated (R-0H-Zn-Cl/S-0H-Zn-Cl), monoprotonated (R-1H-Zn-Cl/S-1H-Zn-Cl), and biprotonated (R-2H-Zn-Cl/S-2H-Zn-Cl) chiral OIMHs with RTP were facilely synthesized. Benefiting from the protonation-enhanced charge transfer (CT), OIMHs exhibited stable photochromism with the crystal color change and luminescence switching, leading to photochromic CPL. The reversible structural transformation between monoprotonated and biprotonated hybrids can be achieved through the regulation of HCl-NH₃ vapor or aqueous solution, accompanied by the switching of circularly polarized RTP behaviors. Importantly, the dissymmetry factors (g_lum) values can be greatly enhanced, which are proportional to the amount of proton, resulting from hydrogen bonding-enhanced chirality amplification. With multi-photoresponsive advantages, these hybrids demonstrated potential applications in anti-counterfeiting and encoding. This work thus provides new insight into developing solid-state photochromism in OIMHs and lays the groundwork for designing chiral OIMHs with stimulus-responsive CPL and RTP.