Controlling Triplet-Harvesting Pathways and Nonlinear Optical Properties in Cu(I) Iodide-Based Polymers through Ligand Engineering
Joy Chatterjee, Riteeka Tanwar, Anupama Setia, Abhijit Chatterjee, Madan D. Ambhore, Mukul Kabir, Pankaj Mandal, Partha Hazra
Abstract
Organic–inorganic hybrid metal halides have become enormously important in optoelectronics, sensing, photosensitization, etc. In this study, we report a structural transition from a staircase configuration to a cubane configuration in Cu(I) iodide-based polymers influenced by the coordination behavior of two different π*-acceptor ligands. The staircase polymer structure, coordinated with 3-cyanopyridine, demonstrates efficient thermally activated delayed fluorescence from (metal+halide)-to-ligand charge transfer [ 1/3 (M+X)LCT] states, with a singlet–triplet energy splitting of ∼9 meV. Conversely, upon replacement of the cyano with an amino group at the same position, a one-dimensional polymeric structure of Cu 4 I 4 cubane-type clusters is formed, which shows strong cluster-centered ( 3 CC) orange emission at room temperature. Temperature-dependent photoluminescence studies indicate that the 3 CC state behaves as a self-trapped excitonic state with significant exciton–phonon coupling having a Huang–Rhys factor of 58.6. Additionally, we report this cubane-type cluster polymer acts as an efficient nonlinear optical material showing third harmonic generation with a χ (3) value of 1.32 × 10 –18 m 2 V –2 and a laser-induced damage threshold of 25.87 GW/cm 2 .