π-Conjugated Surface Modification and Supramolecular Assembly of a Homochiral Zirconium-Embonate Cage for Tunable Optical Properties

Abstract

The unique combination of solution processability, modular synthesis, and post-synthetic modification (PSM) capabilities renders metal–organic cages (MOCs) a highly promising platform for diverse applications. In this work, a pair of pure enantiomers, PTC-377(Λ,S) and PTC-377(Δ,R), were synthesized via selective coordination of π-conjugated chiral cations, [Ag₂(1S,2S-DPEN)(DPPM)]²⁺ and [Ag₂(1R,2R-DPEN)(DPPM)]²⁺, to the vertices of racemic ΔΔΔΔ- and ΛΛΛΛ-Zr₄L₆ (L = embonate) cage precursors, respectively. The chiral resolution and surface modification of the zirconium cage result in a pronounced circularly polarized luminescence (CPL) response. Furthermore, the loading of π-conjugated 1,10-phenanthroline (phen) within the mesoporous channels of PTC-377 yields the composite phen@PTC-377. Thin films of this composite exhibit a dramatically enhanced optical limiting effect, with the normalized transmittance minimized at 0.11—a significant improvement over both the pristine Zr₄L₆ cage (~1) and the parent PTC-377 (~0.65). According to theoretical calculations, the enhanced optical limiting effect originates from the strong π–π stacking at the edge site between phen and the PTC-377 framework, these interactions extend the conjugated system and facilitate efficient charge transfer, thereby enhancing the polarizability and hyperpolarizability of the molecule.

Keywords

Chiral crystalline materials / Zirconium-organic cage / Post-synthetic modification / π-conjugated structure / Optical property

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