Study of Interfacial Charge Transfer from an Electron Rich Organic Molecule to CdTe Quantum Dot by using Stern‐Volmer and Stochastic Kinetic Models

Abstract

Photoinduced electron transfer (PET) from N‐methylaniline (NMA) to a photoexcited CdTe quantum dot (QD*) is studied in toluene. The PET mechanism at low to moderate quencher (NMA) concentrations (<0.08 M) remains mostly collisional with some contributions from QD‐NMA complex formation. However, at high quencher concentrations (>0.10 M), QDs form larger numbers of static complexes with NMA molecules leading to a steep positive deviation in the steady‐state Stern–Volmer curves. An isothermal titration calorimetry (ITC) study confirms the formation of QD‐NMA complexes (K∼150 M−1) at high quencher concentrations. Fitting our experimental data using a stochastic kinetic model indicates that the number of NMA molecules attached per QD at highest NMA concentration (∼0.16 M) used in this study decreases from ∼0.76 to ∼0.47 with reducing the QD size from ∼5.2 nm to ∼3.2 nm. However, the PET rate increases with decreasing QD size, which is commensurate with the observation that the chemical driving force (ΔG) increases with decreasing the QD particle size. We have analyzed the PET kinetics mainly by using Stern‐Volmer fittings. However, in some cases Tachiya's stochastic kinetic model is used for stoichiometric analysis, which seems to be useful only at high quencher concentrations. The measured PET rate coefficients in all the cases are found to be at least an order of magnitude lower when compared to the diffusion‐controlled rate of the reaction medium.

Ultrafast Interfacial Electron Transfer from Graphene Quantum Dot to 2,4-Dinitrotoluene

“…While the lifetime SV plot is fitted solely by eq providing the collisional PET rate (k PET ), the steady-state SV plot is fitted by eq where k PET is fixed from eq . Fitting to the steady-state SV plot provides us the association constant (K) of the GQD–DNT complex. − …”

“…(2) Quenching of GQD emission by air oxygen adds a deleterious effect in the solid-state PET study, but the same will have a subtle effect in the liquid-phase study. Even though the solution-phase study undoubtedly has greater control over reaction stoichiometry, fast PET kinetics study in solution suffers from a major disadvantage where the PET rate levels off to the diffusion-controlled limit of the reaction medium. − …”

Subpicosecond Charge Separation Time Scale at Graphene Quantum Dot Surface

“…Splitting of O 1s peak confirms the presence of C–O (533.5 eV) and CO (532 eV) bonds, respectively (Figure C). Chemical driving force (−Δ G PET ∼ 0.95 eV) of PET reaction was calculated from the oxidation and reduction potentials of DMA and GQD and the band gap energy of GQD obtained from Tauc plot or intersection wavelength of normalized absorption and emission spectra. ,− Details of Δ G PET calculation can be found in the Supporting Information.…”

Femtosecond Upconversion Study of Interfacial Electron Transfer from Photoexcited CsPbBr3 Perovskite Nanocrystal to Rhodamine 6G

“…All inorganic lead halide perovskites (CsPbX 3 ; X is Cl, Br, or I) are in the limelight after their recent entry to the nanoscale dimension. − Easy synthesis, harnessing composition-dependent electrical and optical properties, high emission quantum yield (Φ f ), low exciton dissociation energy, and long carrier diffusion length have paved their way to a broad range of applications starting from light-emitting diodes (LEDs), color-converting phosphors to room-temperature single-photon emitters, low-threshold lasers, and many more. − Recent reports find photovoltaic applications of perovskite nanocrystal (NCs) benefit from easy harvesting of photogenerated high-energy species (i.e., biexcitons, hot carriers, etc.) in perovskite composites, efficient surface passivation of other QDs by perovskites, and long carrier diffusion length in perovskite composites. − In this context, a recent work by Samanta and co-workers is noteworthy.…”