Design and Synthesis of Dual Emissive Phosphorescent Transition Metal Complexes

The design of single molecules with dual emissive properties is challenging because it requires the successful blockage or control of energy transfer processes between different excited states. Despite quite a number of dual luminescent single molecules developed from bridging different emissive moieties, the modification and fine-tuning of the dual emissive properties of these dyads or triads, such as the emission wavelengths and the ratio of the two emission bands, are extremely difficult even though the tuning of each independent emissive moiety is well documented. Any modification of the emissive excited states and/or the linkage of each emissive moiety inevitably alters the energy transfer efficiency between different emissive excited states, leading to an unpredictable change in the dual emission behavior.In the proposed project, different transition metal complexes containing π-accepting ligands with excited-state intramolecular proton transfer (ESIPT) reactivity will be synthesized, and the reactivity, tautomerization equilibrium, electrochemistry and photophysical properties of these complexes will be investigated. The new ESIPT reactivity derived from the metal-to-ligand charge transfer (MLCT) excited state will also be studied. The structure-photophysical property relationship of these dual emissive complexes will be investigated. Based on the judicious design of ligands with a desirable emission energy difference between the tautomeric forms together with the reported blue triplet emitters, dual phosphorescent complexes with white light emission will be synthesized. In addition, complexes with carbene-isocyanide equilibrium will be developed. In summary, this project is expected contribute to basic understanding of the excited state properties, photophysics and reactivity of a new class of transition metal complexes with tautomeric equilibrium. It should also initiate a new direction and a systematic strategy towards the development of dual phosphorescent transition metal complexes suitable for the development of single-molecule white-light phosphorescent materials as well as luminescent sensors and probes.