Prof. Stefan Bernhard, Princeton University

Synthetically Tuned Luminophoric Materials: 3D Displays, Solar Energy Conversion, and Beyond

The research presented here is focused on the design of phosphorescent and fluorescent metal complexes with distinct optical, electrochemical and chiroptical properties. Deliberate synthetic design as well as parallel synthetic methodology is used to tailor these materials for application in organic light emitting devices (OLEDs) and in the photogeneration of hydrogen. The first part of the seminar describes the use of hemicage ligands to improve the photophysical properties, such as luminescence quantum yields and lifetimes through luminophore rigidification. These Ru(II), Zn(II) and Al(III)complexes also exhibit unprecedented electrochemical stability. Modification of the hemicage ligand with a pinene substructure permitted the predetermination of the helicity at the metal center. The emission dissymmetry of these and other enantiopure transition metal complexes was measured and correlated to DFT calculations. Complementing this approach of judicious ligand sphere design was a combinatorial strategy, which yielded libraries of heteroleptic, cyclometalated Ir(III) complexes with a wide range of excited state energies. The structure-property relationships that unfolded in these structurally diverse libraries through ligand permutations were further explored by DFT calculations. These ionic complexes were originally utilized for the color tuning of single-layer OLEDs. Later work was focused on the photo-generation of hydrogen. The parallel synthetic approach was extended to screen these materials in photocatalytic water
reduction and oxidation reactions with a newly developed 16-well photoreactor. Redox catalysts of unprecedented robustness were discovered and the kinetics of these H2 and
O2 evolving reactions were measured in parallel.