Emission Tunability, Triplet State Harvesting, and Photon Up-conversion Properties in Selected Organic-Inorganic Hybrid Cu(I)-Based Frameworks

Abstract

The central motivation of this thesis is to explore the possibility of achieving broadband emission tunability along with investigating several triplet harvesting pathways and non-linear photon up-conversion properties in organic-inorganic hybrid Cu(I)-based frameworks. At first, we showcased that a reaction time-dependent broadband emission tunability can be achieved in a thiol-templated Cu nanocluster system by an in-situ ligand engineering process. Further, we went on to improve the emission yield of the system by effective utilization of triplet excitons in Cu(I)-iodide-based frameworks, where the extent of spin-orbit coupling is much higher. Iodide-bridged Cu2I2 complexes have emerged as potential resources of triplet excitons owing to the strong charge transfer emission and intrinsically high quantum yield. However, shorter Cu-Cu distance can give rise to cluster-centered emissive states in these complexes due to strong Cu···Cu bonding interactions, which can significantly quench the emission yield of the complexes. We proposed a ligand engineering approach, which could successfully eradicate the Cu···Cu bonding interactions by increasing the Cu-Cu distance and thereby activating TADF in iodide-bridged Cu2I2 complex. We further applied the ligand engineering approach in higher-order Cu(I)-iodide frameworks to regulate the triplet harvesting pathways and structure-property relationship. We showcased that a well-designed ligand engineering approach can lead to a structural switch in Cu(I)-iodide-based organic-inorganic polymers. This approach results in a complete paradigm shift in the triplet harvesting pathways of these polymers from charge transfer-based TADF to self-trapped excitonic emission. Moreover, we have explored the non-linear photon up-conversion properties of these frameworks, which can be utilized in generating high-energy photons. These phenomena include third-harmonic generation, two-photon excited luminescence, multi-photon luminescence, and so on, which emerge due to their high charge transfer nature, bulk-phase polarizability, and crystal packing arrangements.