Transition metal redox catalysis is fundamental to a diverse range of processes from natural light harvesting to chemical synthesis. Recently, the merger of transition metal catalysis with photoredox catalysis, called metallaphotocatalysis, has provided a versatile platform to access new reactive pathways. The electronic dynamics of these catalysts following photoexcitation determines their efficiency. Using ultrafast nonlinear spectroscopy, we can map the flow of energy through these electronic states. Here we report the dynamics of a novel series of tripyrrindione molecules which display tunable redox-active chemistry and are candidate systems for metallaphotocatalysis. These molecules are related to linear or macrocyclic oligopyrroles, such as tetrapyrrolic porphyrins as well as bilins, chlorophylls and bacteriochlorophylls. Tripyrroles are uncommon in nature, however, they possess many of the desirable properties of tetrapyrroles. These systems have optical and material properties that make them attractive for the development of new redox-active molecules, for catalytic applications and as optical sensors. Our ultrafast experiments have shown that the dynamics of the tripyrrindione ligands are tuned by hydrogen-bonding interactions between the solute and the solvent. When bonded to copper or palladium metal centers, the tripyrrindione-metal complexes are relatively insensitive to the solvent environment but demonstrate controllable, reversible aggregation. In these systems, the electronic relaxation is temperature dependent and mediated through the metal center.

Ultrafast dynamics of redox-active tripyrrindione molecular systems

ACS Spring Meeting 2021

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