Strong Electronic Coupling of Graphene Nanoribbons onto Basal Plane of a Glassy Carbon Electrode

Zoric, Marija R.; Askins, Erik; Qiao, Xiaoxiao; Glusac, Ksenija D.

doi:10.1021/acsaelm.0c00978

Cited by 11 publications

(10 citation statements)

References 50 publications

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“…The cathodic feature is chemically reversible and exhibits pronounced pH-dependence. Similar behavior was observed previously for bipyrimidine-based nanographenes, 33 and is assigned to a two-electron, two-proton reduction of the bpm moiety to the corresponding dihydro-bipyrimidine (bpmH2) analog (Scheme 1). The bpm reduction feature exhibits a modest current enhancement in the cathodic scan for CVs collected at pH<2.0 (observable in the pH=2 CV, Figure 1a).…”

Section: Resultssupporting

confidence: 84%

Proton-coupled Electron Transfer in a Ruthenium (II) Bipyrimidine Complex in its Ground and Excited Electronic States

Drummer

Weerasooriya

Gupta

et al. 2022

Preprint

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Proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH2)(PF6)] complex, Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH2 in the anodic region. The photophysical behavior of Ru-bpm was studied using steady-state and femtosecond transient UV-vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state of Ru-bpm is described as a (Ru bpm) metal-to-ligand charge transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited state kinetics of Ru-bpm were found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes 1=4 ps and 2=65 ps in aqueous solution. Kinetic isotope effect of 1.75 was observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics of Ru-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the 3MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with the 4 ps lifetime. The formation of such hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the 3MLCT state. The hydrogen-bonded state 3MLCT’ decays to the ground state with a 65 ps lifetime. Such short lifetime is likely associated with the efficient vibrational energy transfer from 3MLCT state to the solvent.

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Section: Resultssupporting

confidence: 84%

Proton-coupled Electron Transfer in a Ruthenium (II) Bipyrimidine Complex in its Ground and Excited Electronic States

Drummer

Weerasooriya

Gupta

et al. 2022

Preprint

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“…In a previous electrochemical (non-photophysical) study, we showed that bipyrimidine units behave as redoxactive electron accepting moieties, undergoing efficient proton-coupled electron transfer processes. 36 In this study, we show that GQD and GNR exhibit excited states with chargetransfer character, where bipyrimidine units serve as electron acceptors, an important property for efficient photoinduced charge separation required in photocatalytic applications. Furthermore, we find that the edge chlorination has a beneficial effect on the excited-state lifetimes of GNRs, due to the significant reduction in the non-radiative decay pathways associated with -stacking between aromatic cores.…”

Section: Introductionmentioning

confidence: 76%

“…The polymerization of 3-Br via Yamamoto coupling yields polymer-3, which is then oxidized to H-GNR using FeCl3. The MS characterization of polymer-3 36 indicates that ribbons up to ~20 nm in length (~16 3H units) are formed, while longer polymer-3 units, which may exist in the H-GNR sample, are not expected to get ionized and detected in the mass spectrometry. The ICl chlorination methods yield Cl-GNR, which have been characterized using XPS and NMR (Section S1, SI).…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

“…27,34 The observed 106 μs lifetime is excellent for potential photocatalysis applications where long-lived excited states are required to provide sufficient time for useful chemical reactions to take place. The charge-transfer character of H-GNR excited states (Figure 1c) is a direct consequence of electron accepting properties of bipyrimidine moieties 36 and enables spatial separation of electrons and holes within the exciton, which is useful for photoinduced electron transfer processes that initiate most photocatalytic reactions. We expect similar charge-transfer states in Cl-GNR given the similarities between H-GQD and Cl-GQD difference density plots (Figure S14, SI).…”

Section: Steady-state Spectroscopymentioning

confidence: 99%

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Long-lived Excited State in a Solubilized Graphene Nanoribbon

Drummer

Glusac

Chen

et al. 2021

Preprint

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Graphene nanoribbons exhibit excellent light-absorbing properties, but often exhibit short excited-state lifetimes that prevent their applications in photocatalysis. Here, we report a long-lived charge-transfer triplet excited state in a well solubilized, chlorinated graphene nanoribbon (Cl-GNR) with edges modified by bipyrimidine (bpm) moieties. The photophysical behavior of Cl-GNR was observed and characterized by steady-state UV-vis absorption and emission spectroscopy, transient absorption spectroscopy on the ps-ms timescale, and density functional theory (DFT) calculations. Both the Cl-GNR and its monomeric subunit, chlorinated graphene quantum dot (Cl-GQD), were synthesized using bottom-up techniques to produce the H- analogs of the compounds followed by edge-chlorination to achieve soluble products. The absorption spectra of Cl-GQD and Cl-GNR appear in the UV-vis range with lowest-energy peaks at 375 and 600 nm, respectively. The excitons in Cl-GNR were found to exhibit charge-transfer character with the bpm edges serving as electron acceptors. DFT calculations indicate that the excitons are relatively localized, spreading over at most two monomeric units of the GNR. Transient absorption spectroscopy shows that singlet excited states of Cl-GQD and Cl-GNR undergo intersystem crossing with ~300 ps lifetime to form triplet state that lasts for 15.7 μs (Cl-GQD) and 106 μs (Cl-GNR). These properties, combined with the ability of bpm sites to coordinate transition metals, make Cl-GNRs promising light-harvesting motifs for photocatalytic applications.

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“…Similarly, it has recently been shown that strong coupling between glassy carbon electrodes can be achieved through basal plane modification with nitrogen-doped GNRs. When the GNRs are determined to be in strong communication with the electrode surface, every ET across the entire pH region (0–14) was coupled to PT 99 . These results point to an important difference between homogeneous and heterogeneous catalysts: while isolated electron transfer events can take place in homogeneous catalysts, they are always coupled by a compensating transfer of charged groups, e.g., protons, in the case of heterogeneous catalysis.…”

Section: Insights From Molecular Modelsmentioning

confidence: 99%

Toward a mechanistic understanding of electrocatalytic nanocarbon

Askins

Zoric

et al. 2021

Nat Commun

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Electrocatalytic nanocarbon (EN) is a class of material receiving intense interest as a potential replacement for expensive, metal-based electrocatalysts for energy conversion and chemical production applications. The further development of EN will require an intricate knowledge of its catalytic behaviors, however, the true nature of their electrocatalytic activity remains elusive. This review highlights work that contributed valuable knowledge in the elucidation of EN catalytic mechanisms. Experimental evidence from spectroscopic studies and well-defined molecular models, along with the survey of computational studies, is summarized to document our current mechanistic understanding of EN-catalyzed oxygen, carbon dioxide and nitrogen electrochemistry. We hope this review will inspire future development of synthetic methods and in situ spectroscopic tools to make and study well-defined EN structures.

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Strong Electronic Coupling of Graphene Nanoribbons onto Basal Plane of a Glassy Carbon Electrode

Cited by 11 publications

References 50 publications

Proton-coupled Electron Transfer in a Ruthenium (II) Bipyrimidine Complex in its Ground and Excited Electronic States

Proton-coupled Electron Transfer in a Ruthenium (II) Bipyrimidine Complex in its Ground and Excited Electronic States

Long-lived Excited State in a Solubilized Graphene Nanoribbon

Toward a mechanistic understanding of electrocatalytic nanocarbon

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