Low Power Photoluminescence and Photochemical Upconversion

The efficient generation of ultraviolet and blue light in molecular systems remains challenging for device technologies such as organic light-emitting diodes. To address this problem we developed a new method utilizing MLCT-sensitized anti-Stokes fluorescence in non-covalent triplet energy transfer assemblies. The method is based on harnessing sequential highly allowed one-photon absorptions in a specially designed photonic system. This can be accomplished using triplet-triplet annihilation (TTA) reactions where the energy stored in two separate excited triplet states are combined to generate a higher energy excited singlet state and a corresponding ground state species. The result is a delayed singlet fluorescence of higher energy relative to the excitation light or the formation of desired chemical products which traditionally requires high energy ultraviolet light excitation. The first chapter describes basic molecular photophysics and photochemistry as they apply to processes in this dissertation. The second chapter discusses the upconverted fluorescence where the upconverted singlet fluorescence from anthracene (An) or 9,10-diphenylanthracene (DPA) in the near-visible region upon excitation with light from the 488 nm or 514.5 nm output of an argon ion laser is observed in deaerated solutions. Various combinations of donor and acceptor have been explored and quantitative data of the efficiency of these systems has been collected. In certain cases, sensitized TTA leads to the efficient production of delayed singlet fluorescence which can be readily visualized at low continuous-wave excitation power (\u3c 5 mW). The third chapter describes the first example of determination of the absolute quantum yield of the Ru(II) sensitized upconverted fluorescence in DPA. The final chapter demonstrates a representative synthetic application where the visible-light sensitized TTA upconversion efficiently drives bimolecular [4 + 4] cycloaddition chemistry between two anthracenes. This is accomplished through selective excitation of Ru(II) diimine complexes. The cycloaddition chemistry traditionally requires high energy ultraviolet light excitation. The potential of applying sensitized TTA in preparative chemistry using anthracene dimerization as a prototypical reaction is shown