Harnessing the reactivity of electrons: Directing radical reactivity through synthetic design, mechanistic control, and material structure.

摘要

The aggressive reactivity of radicals has historically been harnessed in reagents capable of performing difficult chemical transformations, therapeutic agents capable of aggressively targeting tumors, and materials capable of transporting these electrons for use in electronic devices. Within this context, molecules based on enediyne and diazo-ketone functional groups have been synthesized in efforts to develop stable materials that will selectively generate radical species upon external activation. Utilization of porphyrinic chromophores as "light antennas" has allowed photo-chemical generation of carbenes from diazo-keto chlorin scaffolds that are indefinitely stable absent irradiation. The nature and array of products isolated from room-temperature photolysis confirm formation of carbenes upon photolysis. Frozen matrix spectroscopic analysis of the reactive photo-intermediates, in conjunction with computational modeling of their electronic structure, has facilitated mechanistic control of the chlorin radical reactions to direct selective synthesis of unique azeteoporphyrins formed upon Wolff rearrangement of the parent diazo-carbonyl. Additionally, a series of metalloenediynes utilizing tetradentate binding motifs has been synthesized and characterized in efforts to develop chemically switchable molecules that generate diradicals upon addition of a secondary reagent. Activation of these materials towards Bergman and Meyers-Saito cyclization has been demonstrated. Finally, molecular and macromolecular structural analysis via spectroscopy, crystallography and microscopy of a series of thioalkyl porphyrazine liquid-crystalline materials has identified contributions of the central metal ion to the bulk physical properties of these materials. Electrical analysis of the self-assembled nanowires grown from these porphyrazines has revealed them to be highly conductive. Coupled with the demonstration of photo-induced phase switching within these materials, potential micro-electronic applications for these materials are promising.