Long-lived Excited State in a Solubilized Graphene Nanoribbon

23 August 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


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.


graphene quantum dot
graphene nanoribbon
transient absorption spectroscopy
density functional theory
triplet excited state
long-lived excited state

Supplementary materials

(SI) Long-lived Excited State in a Solubilized Graphene Nanoribbon
Details on general methods, synthesis, characterization, steady-state spectroscopy, transient absorption spectroscopy, and computational methods.


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