Chiral Metal-Organic Cluster Induced High Circularly Polarized Luminescence of Metal-Organic Framework Thin Film

Guest-induced host-guest assembly in metal-organic frameworks (MOFs) has become a critical strategy to achieve circularly polarized luminescence (CPL). Herein, chiral metal-organic clusters (MOCs) induced CPL of achiral MOF are reported. Enantiopure titanium-oxo clusters (R/S-TOCs) are effectively loaded into the pores of a fluorescent, highly stable MOF NU-901 thin film by using a liquid-phase epitaxial layer-by-layer encapsulation method. The resulting chiral TOCs@NU-901 MOF thin films exhibit strong chirality, intense photoluminescence, and excellent CPL performance with the highest dissymmetry factor (+/- 0.025) reported so far for the downshifted MOF-based materials. Further, the comparison experiments and density functional theory (DFT) calculations demonstrate that the excellent performance benefited from the strong chirality and charge transfer caused by the significant pi-pi interactions between the host (MOF) and guest (R/S-TOCs). This novel chiral MOCs induced approach provides a powerful toolbox for new host-guest CPL thin film materials.