Abstract
Rhenium(I)-carbonyl-diimine complexes have emerged as promising photocatalysts for carbon dioxide reduction with covalent organic frameworks recognized as perfect sensitizers and scaffold support. Such Re complexes/covalent organic frameworks hybrid catalysts have demonstrated high carbon dioxide reduction activities but with strong excitation energy-dependence. In this paper, we rationalize this behavior by the excitation energy-dependent pathways of internal photo-induced charge transfer studied via transient optical spectroscopies and time-dependent density-functional theory calculation. Under band-edge excitation, the excited electrons are quickly injected from covalent organic frameworks moiety into catalytic Rhenium
I
center within picosecond but followed by fast backward geminate recombination. While under excitation with high-energy photon, the injected electrons are located at high-energy levels in Rhenium
I
centers with longer lifetime. Besides those injected electrons to Rhenium
I
center, there still remain some long-lived electrons in covalent organic frameworks moiety which is transferred back from Rhenium
I
. This facilitates the two-electron reaction of carbon dioxide conversion to carbon monoxide.
Re complexes within covalent organic frameworks have emerged as promising photocatalysts for CO
2
reduction. Here, authors identify a high-energy electron transfer pathway during CO
2
reduction that results in longer-lived excited states than a low-energy electron transfer pathway.