Gatekeeping Effect of Ancillary Ligand on Electron Transfer in Click Chemistry‐Linked Tris‐Heteroleptic Ruthenium(II) Donor–Photosensitizer–Acceptor Triads

Abstract

Stable charge‐separated states are key features for using light in various types of solar cells and a broad range of photocatalytic applications. So far, molecular systems often suffer from increased charge recombination after initial excitation. Herein, the scope of molecular model systems for intramolecular electron transfer and charge separation by applying copper‐catalyzed click chemistry to covalently functionalize tris‐heteroleptic ruthenium(II) complexes to yield donor–photosensitizer–acceptor triads with 1,4‐dihydro‐N‐benzyl‐nicotinamide (BNAH) as donor and N‐methyl‐4,4´‐bipyridinium (MQ+) as acceptor is studied. Two triads with electron‐withdrawing or electron‐donating ancillary 2,2´‐bipyridyl ligands are synthesized and their light‐induced intramolecular electron transfer and long‐lived charge‐separated states (τ = 0.8 ms and τ = 1.5 ms) are characterized using steady‐state and time‐resolved spectroscopy and electrochemistry. Additionally, it is found that the charge‐separated state resides on different parts of the molecule within these two triads, allowing for selective directionality of charge transfer within a molecule.

Better Covalent Connection in a Molecular Triad Enables More Efficient Photochemical Energy Storage

“…The formation and decay of charge-separated states by photoinduced electron transfer have therefore received enormous attention, and many donor–acceptor compounds have been investigated over the past five decades. , In fully integrated molecular compounds with all reaction components linked covalently to one another, the overall photochemical reactivity is not limited by diffusion, , and therefore, direct insight into the photoinduced electron (or energy) transfer events is obtainable. In the simplest case, this approach focuses on molecular dyads comprising merely the donor and the acceptor, but often molecular triads containing a separate photosensitizer in addition to the donor and the acceptor are explored. − In rarer cases, even tetrads or pentads, for example involving secondary donor and acceptor moieties, become of interest. − …”

“…In the simplest case, this approach focuses on molecular dyads comprising merely the donor and the acceptor, but often molecular triads containing a separate photosensitizer in addition to the donor and the acceptor are explored. 6 − 23 In rarer cases, even tetrads or pentads, for example involving secondary donor and acceptor moieties, become of interest. 24 − 28 …”