Transient absorption spectroscopic studies of linear polymeric photocatalysts for solar fuel generation

Abstract

Organic polymer photocatalysts have garnered much interest in recent years, notably because of their photocatalytic activity toward hydrogen production from water. However, to rationalize the differences in activities between photocatalysts, it is crucial that their photodynamics are understood. Here, we provide an accessible introduction to the use of transient ultraviolet/visible absorption spectroscopy to study the photodynamics of linear polymeric photocatalysts through a review of literature studies. The principles of transient absorption (TA) spectroscopy, and the apparatus required, are briefly described. A step-by-step method to identify key species and unravel their kinetics is provided through exemplar spectra reported within the literature. This review provides the foundations for researchers new to the field of TA spectroscopy to design, perform, and interpret their own TA experiments to probe the photodynamics of organic photocatalysts.

Triazine-Based Covalent Organic Framework for Photocatalytic Water Oxidation: The Role of Bipyridine Ligand and Cobalt Coordination

“…Finally, compartment 4 decays on a time scale longer than that probed by the experiment. We note that the position of the broad PIA observed at negative delays (−1 ps, Figure S12) corresponding to a pump–probe delay of ∼100 μs, is also in excellent agreement with the TA feature assigned to the charge-separated states in the related CTF materials, with the longevity of this feature consistent with assignment to species with charge-separated character . As deposited, the dominant oxidation state of Co is +2 in TAPT-Bpy-COF-Co-3.…”

“…Similar efficient e – scavenging is expected in the photoactivity measurements reported here, resulting in the formation of long-lived h + polaronic species. Intriguingly, transient species with lifetimes on the microsecond time scale are typically only observed in the presence of sacrificial reagents such as ascorbic acid and triethylamine, with alcohols shown to be inactive as electron donors in organic photocatalysts …”

“…We note that the position of the broad PIA observed at negative delays (−1 ps, Figure S12) corresponding to a pump−probe delay of ∼100 μs, is also in excellent agreement with the TA feature assigned to the charge-separated states in the related CTF materials, with the longevity of this feature consistent with assignment to species with charge-separated character. 39 As deposited, the dominant oxidation state of Co is +2 in TAPT-Bpy-COF-Co-3. A large increase in absorption is expected across the visible wavelength range upon oxidation of Co II to Co III , 40 which is not observed in the TA or decay associated spectra shown in Figure 4.…”

“…Intriguingly, transient species with lifetimes on the microsecond time scale are typically only observed in the presence of sacrificial reagents such as ascorbic acid and triethylamine, with alcohols shown to be inactive as electron donors in organic photocatalysts. 39…”

Long‐Lived Charges in Y6:PM6 Bulk‐Heterojunction Photoanodes with a Polymer Overlayer Improve Photoelectrocatalytic Performance

“…[8] Significant progress has been made recently in the performance of organic photoelectrodes based on conjugated polymers with the use of co-catalysts or metal overlayers to aid charge separation and drive desirable reduction/oxidation reactions. [1,3,9,10] However, whilst there have been extensive studies of charge carrier dynamics in organic photovoltaics, and more recently studies of such dynamics in polymeric photocatalysts in suspension, [11,12] studies of these dynamics in organic photoelectrodes have been very limited to date.…”