Diffusion of Solvent-Separated Ion Pairs Controls Back Electron Transfer Rate in Graphene Quantum Dots

Huang

et al. 2022

JACS Au

The sunlight-driven reduction of CO 2 into carbonaceous fuels can lower the atmospheric CO 2 concentration and provide renewable energy simultaneously, attracting scientists to design photocatalytic systems for facilitating this process. Significant progress has been made in designing high-performance photosensitizers and catalysts in this regard, and further improvement can be realized by installing additional interactions between the abovementioned two components, however, the design strategies and mechanistic investigations on such interactions remain challenging. Here, we present the construction of molecular models for intermolecular π–π interactions between the photosensitizer and the catalyst, via the introduction of pyrene groups into both molecular components. The presence, types, and strengths of diverse π–π interactions, as well as their roles in the photocatalytic mechanism, have been examined by 1 H NMR titration, fluorescence quenching measurements, transient absorption spectroscopy, and quantum chemical simulations. We have also explored the rare dual emission behavior of the pyrene-appended iridium photosensitizer, of which the excited state can deliver the photo-excited electron to the pyrene-decorated cobalt catalyst at a fast rate of 2.60 × 10 6 s –1 via co-facial π–π interaction, enabling a remarkable apparent quantum efficiency of 14.3 ± 0.8% at 425 nm and a high selectivity of 98% for the photocatalytic CO 2 -to-CO conversion. This research demonstrates non-covalent interaction construction as an effective strategy to achieve rapid CO 2 photoreduction besides a conventional photosensitizer/catalyst design.

Section: Discussionmentioning

confidence: 87%

Co-facial π–π Interaction Expedites Sensitizer-to-Catalyst Electron Transfer for High-Performance CO₂ Photoreduction

Huang

et al. 2022

JACS Au

“…Hence, the other time constant (26 ps) is attributed to the recombination time of electrons on GQDs with either VB hole or trapped hole of CdTe QDs. , Here, one may argue about the absence of distinct PA signal for GQD radical anion, formed after accepting the electron from photoexcited CdTe QDs. The absence of GQD radical anion can be explained as follows: (i) the GQD radical anion might absorb in the infrared region, which is beyond our instrumental detection limit, or (ii) the GQD radical anion peak is indistinguishable from the PA signal of CdTe QDs because of the extremely low absorption coefficient of GQD radical anion compared to the PA signal from CdTe QDs . Thus, the overall charge-transfer dynamics in the current system can be summarized as shown in Scheme , which accounts for the electron transfer (<100 fs) from photoexcited CdTe QDs to GQDs with hole trapping (2.8 ps) by surface defects followed by recombination of charge carriers (26 ps).…”

Section: Resultsmentioning

confidence: 99%

Enhanced Charge Transport and Excited-State Charge-Transfer Dynamics in a Colloidal Mixture of CdTe and Graphene Quantum Dots

et al. 2019

Self Cite

Semiconductor quantum dot (QD)–graphene composites are promising materials for photovoltaics and photocatalysis because of efficient charge extraction and transport property of graphene. Analysis of their ultrafast carrier-transfer dynamics has been limited to only QD–graphene sheets, such as CdTe–graphene sheets and CdS–graphene sheets. Herein, we investigate the carrier-transfer dynamics of CdTe QDs (CdTe QDs) in the presence and absence of graphene QDs (GQDs) by using femtosecond transient absorption spectroscopy. Although the surfaces of both the QDs are in negatively charged state, as evident from the zeta potential measurements, we observed a strong excited-state interaction between two similarly charged QDs, leading to an efficient quenching of the excitonic emission of the CdTe QDs in the presence of GQDs. A detailed analysis of the rise time and 1S bleach recovery provides the evidence of electron transfer from CdTe QDs to GQDs with the hole-trapping process by surface defects. On the basis of the mechanistic study, an overall charge-transfer scheme that accounts for the faster bleach recovery of CdTe QDs in the presence of GQDs is proposed. Moreover, we have evidenced the consequences of charge transfer through the measurements of improved four-probe photoconductivity (from 1.39 (±0.12) × 10–4 S m–1 to 1.47 (±0.24) × 10–3 S m–1) and decreased charge-transfer resistance [from 6944 (±0.3) to 5761 (±0.3) Ω] exhibited by CdTe QDs in the presence of GQDs. These findings described in the present study are hoped to open up design strategies for developing light-harvesting inorganic–organic hybrid QD assemblies with better efficiency.

Phys. Chem. Chem. Phys.

“…Furthermore, the range of k q values (10 9 -10 10 M À1 s À1 ) suggests that the luminescence quenching from the singlet state is diffusion-controlled. 29,37,38 From a mechanistic point of view, intramolecular proton transfer can be ruled out in the process as DEA is a tertiary amine. Moreover, the absence of overlap between the quencher absorption spectra and the emission spectra of the isomers eliminates the possibility of excited state energy transfer between the donor-acceptor pairs.…”

Section: Photophysical Investigation Of the Regioisomers In The Prese...mentioning

confidence: 99%

“…The oxidation potential value of DEA was obtained from the literature. 38,39 On the basis of the reduction potentials calculated from CV experiments, the Gibbs free energy for the excited state electron transfer process between each isomer and DEA was estimated using the modified Rehm-Weller equation, 40…”

Section: Electrochemistry and Calculation Of Free Energy Changes Of Petmentioning

confidence: 99%

Effect of positional isomerism on the excited state charge transfer dynamics of anthracene-based D–π–A systems

Pratihar

Prasad

2023

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