Photoinduced Electron Transfer from Various Aniline Derivatives to Graphene Quantum Dots

Abstract

The present study utilizes the luminescence nature of the graphene quantum dots (GQDs) to analyze the mechanistic aspects of the photoinduced electron transfer (PET) processes between GQDs and aniline derivatives. A systematic investigation of PET from various aniline derivatives to GQDs has been presented. Solution-processable GQDs have been synthesized from graphene oxide (GO) at 200 °C. The as-synthesized GQDs exhibit a strong green luminescence at 510 nm, upon photoexcitation at 440 nm. Various aniline derivatives (aniline, N-methylaniline, N,N'-dimethylaniline, N-ethylaniline, N,N'-diethylaniline, and N,N'-diphenylaniline) have been utilized as electron donors to probe the PET process. Results from UV-visible absorption and steady-state and time-resolve luminescence spectroscopy suggest that the GQDs interact with the aniline derivatives in the excited state, which results in a significant luminescence quenching of the GQDs. The bimolecular rate constants of the dynamic quenching have been deduced for various donor-acceptor systems, and the values are in the range of (1.06-2.68) × 10(9) M(-1) s(-1). The negative values of the free energy change of the electron transfer process suggest that PET from aniline derivatives to GQDs is feasible and could be responsible for the luminescence quenching. The PET has been confirmed by detecting radical cations for certain aniline derivatives, using a nanosecond laser flash photolysis setup. The present study shows that among the various types of graphene systems, GQDs are better candidates for understanding the mechanism of PET in graphene-based donor-acceptor systems.

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“…The following Rehm-Weller equation (eqn (4)) has been utilized to calculate the free energy change associated with the PET process. 76,77…”

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“…These observation clearly depict formation of the adduct between GQDs and DOAZOC1. The absence of new absorption peaks in the mixture of GQDs and DOAZOC1 indicates that no non‐emissive substance is formed during the complexing between GQDs and DOAZOC1 and also there is no ground state interaction between them …”

“…Since, there is not as much overlap between the absorption spectra of DOAZOC1 and the emission peak of the GQDs (Figure S2, ESI), the fluorescence quenching of the GQDs by DOAZOC1 may be due to the photo‐induced electron transfer (PET) and the hydrogen bonding between GQDs and DOAZOC1. GQDs are a good electron acceptor, whereas DOAZOC1 with two nitrogen atoms is capable of donating electrons …”

“…The absence of new absorption peaks in the mixture of GQDs and DOAZOC1 indicates that no non-emissive substance is formed during the complexing between GQDs and DOAZOC1 [22] and also there is no ground state interaction between them. [23] The GQDs show a strong green fluorescence under UV illumination with a broad emission peak at 435 nm and also have a quantum yield of 3.6%. [20] When a solution of DOAZOC1 in methanol at a concentration of 10 À4 M is added to GQDs solution, a fluorescence quenching of GQDs occur.…”

“…GQDs are a good electron acceptor, [24] whereas DOA-ZOC1 with two nitrogen atoms is capable of donating electrons. [23] Fluorescence lifetime (t) measurement is used to understand the excited state quenching mechanism of GQDs. The fluorescence lifetime of GQDs and GQDs-DOAZOC1 is assessed by time resolved photoluminescence measurements using 340 nm LED source.…”