Role of Emissive and Non‐Emissive Complex Formations in Photoinduced Electron Transfer Reaction of CdTe Quantum Dots

Bharadwaj, Kiran; Choudhary, Himanshu; Hazra, Soumitra; Ghosh, Subhadip

doi:10.1002/asia.201901147

Cited by 15 publications

(19 citation statements)

References 47 publications

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“…We fitted our PET data with two models: (1) Tachiya's stochastic kinetic model and (2) Stern‐Volmer analysis with some modifications. Tachiya's stochastic model has been used in several occasions where QD emission is quenched by PET and FRET processes . By assuming the presence of trap sites at QD surface this model has nicely explained the non‐exponential nature of QD's fluorescence lifetime profile.…”

Section: Resultsmentioning

confidence: 99%

“…In order to calculate the mean number of bound NMA molecules per QD at high quencher concentrations (>0.10 M) and thereby PET rate coefficients, we assumed NMA molecules are attached to QD following Poisson distribution . The excited state decay of QD* in the presence of average m number of attached quencher molecules (and m t number of trap sites) per QD is expressed by following Equation :

true I ((), t, m) = I_{0} prefixexp ([], - k_{0} t - m ({}, 1 - prefixexp ((), - k_{q} t)) - m_{t} ({}, 1 - prefixexp ((), - k_{q t} t)))

…”

Section: Resultsmentioning

confidence: 99%

“…A survival probability function [S q (t,m)] was derived by normalizing Equation (1) by Equation (2), yielding:

true S_{q} ((), t, m) = \frac{I ((), t, m)}{I ((), t)} = I_{0} prefixexp ([], - m ({}, 1 - prefixexp ((), - k_{q} t)))

…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2020

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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.

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Section: Resultsmentioning

confidence: 99%

true I ((), t, m) = I_{0} prefixexp ([], - k_{0} t - m ({}, 1 - prefixexp ((), - k_{q} t)) - m_{t} ({}, 1 - prefixexp ((), - k_{q t} t)))

…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2020

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“…(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. − …”

Section: Introductionmentioning

confidence: 99%

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

2021

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Ultrafast photoinduced electron transfer (PET) from a photoexcited graphene quantum dot (GQD*) to an electron-deficient molecule 2,4-dinitrotoluene (DNT) is studied in a water−methanol mixture (1:1 by volume) at different temperatures (5 °C−60 °C). The temperature-dependent study reveals that quenching of GQD emission by DNT is a complex process, where use of collisional or static quenching alone in the fitting model cannot fit the entire time regime of the kinetics. Irrespective of temperature, the collisional quenching rate obtained from the TCSPC lifetime quenching study appears at the upper limit of the bimolecular diffusion-controlled rate of the medium. The weak solubility of DNT in the polar solvents leads to GQD−DNT complex formation through hydrophobic interactions, allowing one to obtain a diffusion-free ultrafast PET timescale of the complex using a femtosecond upconversion setup. GQD−DNT complex formation is manifested by the heat change in the isothermal titration calorimetry (ITC) study upon mixing of DNT with GQD. Findings of our work would reinforce the understanding of the interfacial charge transfer process of GQD and thereby expand the promises to its real applications, especially in sensing and photovoltaics where materials with ultrafast PET are highly desirable.

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“…In the case of HC blinking, a hot carrier is trapped long before it relaxes to the band edge. This trapped HC relaxes rapidly, causing a drastic drop in emission intensity without changing much of its lifetime. − Suppression of these relaxation channels through surface engineering has evolved as a popular technique, successfully applied on metal chalcogenide QDs. − Similar surface treatments have been employed for perovskite NCs as well which produce brighter particles, largely free from blinking or intermittency. ,− A mechanistic understanding of the trap-state-induced carrier recombination in NCs causing the PL fluctuations is of paramount importance for further realizing their photovoltaic and optoelectronic applications.…”

mentioning

confidence: 99%

Revealing Explicit Microsecond Carrier Diffusion from One Emission Center to Another in an All-Inorganic Perovskite Nanocrystal

Das

Mishra

Ghosh

2021

J. Phys. Chem. Lett.

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Blinking of freely diffusing CsPbBr 3 nanocrystals (NCs) is studied using fluorescence lifetime correlation spectroscopy (FLCS). Emitted photons from each NCs are assigned to an emission state (exciton or trap) based on their lifetime. Subsequently, an intrastate autocorrelation function (ACF) and an interstate cross-correlation function (CCF) are constructed. Fitting of the AFCs with an analytical model shows that, at low excitation power, the microsecond blinking timescale of the exciton state matches well with that of the trap state. Most interestingly, both of those timescales further correlate with the microsecond growth timescale of the CCF. The strong anti-correlation of the CCF along with the stretched exponential nature of the blinking kinetics confirms the involvement of carrier diffusion and dispersive trap states in NC blinking. At high excitation power, enhanced sample heterogeneity causes a more dispersive blinking. To the best of our knowledge, this is the first report of a NC blinking study using a single-molecule-based FLCS technique.

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Role of Emissive and Non‐Emissive Complex Formations in Photoinduced Electron Transfer Reaction of CdTe Quantum Dots

Cited by 15 publications

References 47 publications

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

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

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

Revealing Explicit Microsecond Carrier Diffusion from One Emission Center to Another in an All-Inorganic Perovskite Nanocrystal

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