Single-Sized CdSe Nanocrystals with Bandgap Photoemission via a Noninjection One-Pot Approach

Yu, Kui; Ouyang, Jianying; Zaman, Md. Badruz; Johnston, Dennis A.; Yan, Fu Jian; Li, Grace; Ratcliffe, Christopher I.; Leek, Donald M.; Wu, Xiaohua; Stupak, Jacek; Jakubek, Zygmunt J.; Whitfield, Dennis M.

doi:10.1021/jp809990a

Cited by 69 publications

(149 citation statements)

References 58 publications

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“…Unlike gel permeation chromatography (GPC), PFG NMR is less dependent on the choice of solvent and has stimulated NMR researchers to explore the applicability of NMR to probe MWD of various polymeric systems. [ 4,5 ] Rather frequently, we have noticed that the pulsed gradient stimulated echo (PGSTE) NMR response of various…”

Section: Introductionmentioning

confidence: 99%

Molecular Weight Distribution Characteristics (of a Polymer) Derived from a Stretched‐Exponential PGSTE NMR Response Function—Simulation

Gong

Hansen

Chen

2012

Macro Chemistry & Physics

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Assuming the signal response in a pulsed gradient stimulated echo (PGSTE) experiment (on a polymer) to be described by a simple stretched-exponential function (SEF) and knowing the scaling law between diffusivity and molecular weight, the molecular weight distribution (MWD) characteristics (kurtosis, skewness, moment, and width) are derived and compared to the corresponding distribution characteristics obtained by a log-normal function fi t (to the same MWD). Also, the challenge involved in obtaining a reliable weight average molecular weight from an SEF response function is discussed.This paper was amended because of mistakes in the equations 11, A3, and A6. polymers in solution can be well approximated by a stretched exponential function (SEF). [ 6 ] Because of the inherent nature of the PGSTE NMR experiment, the signal response from a polymer dissolved in a solvent can be represented by the Laplace transform (LT) of a distribution function, namely, the distribution of diffusivities. Or, alternatively, the distribution function can be expressed by the inverse Laplace transform (ILT) of the response function. It is well known, however, that this is an illposed numerical problem of particular complexity. However, it is known that the ILT of an SEF can be expressed explicitly by a series expansion, [ 7 ] which then bypass the numerical problem of performing an ILT of a SEF.We recently presented an alternative approach to overcome the above numerical problem [ 8 ] whereby a numerical Laplace transform of a log-normal distribution (LND) function was performed and the resulting transform was fi tted to an SEF. By applying the well-known relation between the molecular weight and molecular diffusivity, two empirical equations relating the two SEF parameters of the PGSTE NMR response function and the two corresponding parameters of the log-normal molecular weight distribution (LNMWD) were derived. The above method is, by nature, somewhat approximate as it implicitly

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Section: Introductionmentioning

confidence: 99%

Molecular Weight Distribution Characteristics (of a Polymer) Derived from a Stretched‐Exponential PGSTE NMR Response Function—Simulation

Gong

Hansen

Chen

2012

Macro Chemistry & Physics

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“…As one of the most important II-VI nanocrystals, cadmium selenide (CdSe) becomes a 'model' nanocrystal system for a hotspot of basic studies on the photoelectrical properties of nanocrystals because of its accessibility of high-quality and stability [11]. Recently, the family of colloidal CdSe with a narrow-sized distribution, which is similar to regular nanocrystals, has attracted much attention of the researchers [12][13][14][15][16][17][18][19][20][21]. The CdSe nanocrystals with the narrow-sized distribution hold great promising for the various applications based on a rational design supported by the understanding of nucleation and growth [16].…”

Section: Introductionmentioning

confidence: 99%

“…Yu et al prepared multiple families of CdSe with a narrow bandgap via non-injection one-pot syntheses, showing sharp absorption and emission peaks [19]. Results demonstrated that low acid-to-Cd and high Cd-to-Se feed molar ration are critical for preparing the narrow-sized CdSe [20]. In addition, they proposed a thermodynamic equilibrium driven approach for the formation of CdSe nanocrystals, which featured highly synthetic reproducibility [21].…”

Section: Introductionmentioning

confidence: 99%

Bowl-shaped superstructures of CdSe nanocrystals with the narrow-sized distribution for a high-performance photoswitch

Zhang

Shen

Feng

et al. 2015

Chemical Physics Letters

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“…Unlike GPC, PGSE NMR is less dependent on the choice of solvent and has stimulated NMR researchers to explore the applicability of NMR to probe MWD of various polymeric systems. [4,5] A particular challenge is related to the data processing of the PGSE NMR decay curves to obtain reliable relations between the distribution of diffusivity and the MWD, e.g., bi-exponential fitting, [6] sum of one-parameter functions (e.g., convoluted exponentials, as well as pure exponentials) using a program denoted SPLMOD, [7] component resolved (CORE) [8] and direct exponential curve resolution algorithm (DECRA). [9] When dealing with complex samples showing severe peak overlap with small differences in derived diffusion coefficients, one may apply multivariate curve resolution (MCR), MCR alternating least square (MCR-ALS) analysis, [10] MCR with non-linear least square regression (MCR-NLR) [11] and Maximum entropy (MaxEnt) processing techniques.…”

Section: Introductionmentioning

confidence: 99%

A Simple Access to the (Log/Normal) Molecular Weight Distribution Parameters of Polymers Using PGSTE NMR

Gong

Hansen

Chen

2011

Macro Chemistry & Physics

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A log/normal MWD is characterized by two parameters, its mean molecular weight M0 and width σ. It is demonstrated how these parameters can be obtained by model fitting a stretched exponential function (SEF), as characterized by two parameters β and DS, to the PGSTE response curve. Based on simulations, two general empirical equations relating β and DS to M0 and σ are found. The model enables the MWD characteristics to be determined if the scaling law between diffusivity and molecular weight is known. The sensitivity and relative error of σ and M0 are discussed and the applicability of the model is illustrated by analyzing experimental NMR response curve of some PEO samples. The key advantages of this technique are its simplicity, numerical robustness, and reliability. magnified image

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Single-Sized CdSe Nanocrystals with Bandgap Photoemission via a Noninjection One-Pot Approach

Cited by 69 publications

References 58 publications

Molecular Weight Distribution Characteristics (of a Polymer) Derived from a Stretched‐Exponential PGSTE NMR Response Function—Simulation

Molecular Weight Distribution Characteristics (of a Polymer) Derived from a Stretched‐Exponential PGSTE NMR Response Function—Simulation

Bowl-shaped superstructures of CdSe nanocrystals with the narrow-sized distribution for a high-performance photoswitch

A Simple Access to the (Log/Normal) Molecular Weight Distribution Parameters of Polymers Using PGSTE NMR

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