Design of a Triple Emissive Cu₄I₄ Coordination Polymer through Ligand Engineering

Through rational ligand design, the coordination polymer 1D-[Cu₄(μ₃-I)₄(μ₂-L1)₂]_n (CP1; L1 = 1,1-(1'-naphthylthio)methane) has been predictably prepared from CuI and L1 in acetonitrile where both the node, closed cubane Cu₄(μ₃-I)₄ cluster, and the assembling ligand containing naphthyl aromatic pendants are known to be emissive. At liquid nitrogen temperature, CP1 exhibits simultaneously three long-lived emissions centered at 573, 732, and 785 nm, decaying in the ms time scale (∼7.1 ms), which are readily assigned to triplet metal/ligand-to-ligand charge transfer (³ M/XLCT), ligand-centered (³LC; i.e., ³ππ*), and excimer (³excimer), respectively. These assignments, which strikingly diverge from the classical low-energy cluster-centered (³CC) emission emerging from the Cu₄(μ₃-I)₄ cluster, were based on in-depth photophysical studies and advanced quantum simulations by density functional theory (DFT) and time-dependent DFT (TD-DFT), which also calculated the emission maxima with high precision and degree of agreement.