Cinchonidine vs Cinchonine: Stereochemical Control of Architecture and Circularly Polarized Luminescence in Chiral Cu4I4–Cluster-Based Coordination Polymers

Abstract

Abstract Employing the epimeric ligands, cinchonidine (L1) and cinchonine (L2), two chiral Cu(I) coordination polymers were synthesized: a 1D chain Cu4I4(L1) and a 3D framework Cu4I4(L2). Structural analyses reveal that Cu4I4(L1) incorporates interconnected distorted gyroscope-like and cubane-type Cu4I4 clusters, whereas Cu4I4(L2) comprises solely cubane-type Cu4I4 clusters. This architectural divergence could be attributed to the distinct spatial preferences of the two N-donor atoms in the epimeric ligands. Photoluminescence studies show that Cu4I4(L1) emits orange light with a single broad band (λem = 614 nm, ΦPL = 21.03%), while Cu4I4(L2) displays yellow emission consisting of multiple bands (λem = 575 nm, ΦPL = 1.32%). DFT calculations correlate these differences to the variations in frontier orbital distributions and electronic transition pathways. Notably, the two compounds exhibit distinct circularly polarized luminescence with maximum glum values of +6.1 × 10–3 for Cu4I4(L1) and –2.4 × 10–3 for Cu4I4(L2). This work illustrates how subtle stereochemical differences in epimeric ligands direct the structural self-assembly of chiral Cu(I)-cluster-based coordination polymers, thereby tuning their photophysical and chiroptical properties, and provides a valuable guideline for designing CPL-active Cu(I)-cluster-based materials.