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Effect of small molecule additives in the prenucleation stage of
semiconductor CdSe quantum dots
Liu, Yuanyuan; Willis, Maureen; Rowell, Nelson; Luo, Wenzhi; Fan,
Hongsong; Han, Shuo; Yu, Kui
Effect of Small Molecule Additives in the Prenucleation Stage of
Semiconductor CdSe Quantum Dots
Yuanyuan Liu,
†Maureen Willis,
†,‡Nelson Rowell,
§Wenzhi Luo,
†Hongsong Fan,
∥Shuo Han,
*
,†and Kui Yu
*
,†,∥,⊥†
Institute of Atomic and Molecular Physics, Sichuan University, 610065 Sichuan, P. R. China ‡
School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, U.K. §
National Research Council Canada, Ottawa, Ontario K1A 0R6, Canada ∥
Engineering Research Center in Biomaterials, Sichuan University, 610065 Sichuan, P. R. China ⊥
State Key Laboratory of Polymer Materials Engineering, Sichuan University, 610065 Sichuan, P. R. China
*
S Supporting InformationABSTRACT: For the addition of small molecules in the prenucleation stage of colloidal CdSe conventional quantum dots (QDs), there is insufficient knowledge regarding what are advantageous circumstances. Here, we present a study about such addition. When CH3COOH or Zn(OOCCH3)2 is added in the prenucleation stage (at 120 °C) of a
reaction consisting of cadmium myristate (Cd(OOC(CH2)12CH3)2, Cd(MA)2made from
CdO) and Se powder in 1-octadecene (ODE), CdSe magic-size clusters (MSCs) exhibiting a single sharp absorption doublet at 433/460 nm are synthesized in a single-ensemble form (around 220 °C). We demonstrate that such small molecule addition suppresses the nucleation and growth of QDs and thus directs a competitive process to the formation of MSCs. The present study provides insight into the individual but linked pathways to forming CdSe QDs and MSCs and introduces new avenues to improve the production of MSCs through the addition of small molecules in the prenucleation stage.
V
ery recently, a two pathway model has been proposed for the formation of colloidal semiconductor quantum dots (QDs).1 This model hypothesizes that there exist two individual but linked pathways during the prenucleation stage of QDs. The prenucleation stage, which occurs prior to nucleation and growth of QDs, is also termed as the induction period (IP).2In one of the two proposed pathways, monomers and fragments formed in the prenucleation stage lead to nucleation and growth of QDs, as suggested by the conventional LaMer model of classical nucleation theory (CNT).3−5 In the other pathway, the self-assembly of cation(M = Cd and Zn) and anion (E = S, Se, and Te) precursors is postulated to result in the formation of magic-size clusters (MSCs) via structural transformations from their special precursor compounds formed in the prenucleation stage.6−11
The precursor compounds of MSCs are transparent in optical absorption. Importantly, the formation of one precursor compound from one assembled species (via dense phase reactions) occurs often before that of the monomer and fragment, while the growth of QDs is able to reduce the precursor compound via its fragmentation.
MSCs and QDs differ from each other in many respects.12,13 For example, the optical absorption bandwidth of MSCs is narrower than that of QDs, due to the tighter size distribution of MSCs. The narrow size distribution is a direct result of structural stability of MSCs. Also, for samples extracted from a reaction batch, the absorption feature of MSCs is at constant
wavelengths almost, while that of QDs often continuously red shifts due to QD growth in size. Two distinct types of MSCs have been reported. One type exhibits one sharp absorption singlet;1,6−10,12−14the other type displays one sharp absorption
doublet.11,14−25The two types are referred to as sMSCs and dMSCs, respectively.11For dMSCs, CdTe dMSC-371 with one sharp absorption doublet at ∼350/371 nm was recently reported to evolve from IP samples of cadmium acetate (Cd(OOCCH3)2, Cd(OAc)2) and tri-n-octylphosphine
tel-luride (TeTOP).11
The addition of small molecules, such as an acetate salt Cd(OAc)2 or Zn(OAc)2, was shown to produce CdSe
nanocrystals (NCs) exhibiting one sharp absorption doublet from reactions with cadmium myristic (Cd(OOC-(CH2)12CH3)2, Cd(MA)2prepared from CdO) and Se powder
in 1-octadecene (ODE).14,26,27 Critically, the small molecule was added at an elevated temperature such as 160 °C, at which point nucleation and growth of CdSe QDs had already taken place.14 Thus, the resulting product consisted of both CdSe QDs and dMSCs; to remove the QDs produced, tedious purification had to be performed, which also led to the self-assembly of the dMSCs to nanoplatelets with 1-dimensional
Received: September 30, 2018 Accepted: October 18, 2018 Published: October 23, 2018
pubs.acs.org/JPCL
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quantum confinement.14,15 To the best of our knowledge, there has been no systematic study reported regarding the addition of the small molecules within the prenucleation stage of CdSe QDs.
Here, we report a deliberate study about the addition of small molecules during the prenucleation stage of CdSe QDs. Small molecules, especially those containing the acetate group CH3COO−, are usually present in the synthesis of colloidal
CdSe MSCs, which are particularly characterized by a single, relatively sharp absorption doublet, a property that is distinctly different from those of conventional CdSe QDs.14−17,26−28
Accordingly,Figure 1addresses the reaction of Cd(OAc)2and
Se in ODE. In order to suppress the presence of QDs, the addition of HOAc in the prenucleation stage (at 120 °C) of the same reaction of Cd(OAc)2and Se in ODE is investigated.
To better control the presence of HOAc, the reactions of Cd(MA)2 (made from CdO) and Se in ODE are developed
with the addition of HOAc or Zn(OAc)2in the prenucleation
stage (Figures 3−5). All the reactions have a fixed feed molar ratio of 4Cd to 1Se and a fixed Se concentration of 30 mmol/ kg in ODE. We show that when a reaction of Cd(MA)2and Se
in ODE is heated from room temperature and the addition of CH3COOH (HOAc) or Zn(OAc)2 is performed at 120 °C,
the resulting product at 220 or 240 °C is single-ensemble CdSe dMSCs exhibiting a single sharp absorption doublet at 433/ 460 nm and without QDs. The ensemble is labeled as dMSC-460. The small molecule addition suppresses the nucleation and growth of QDs and facilitates the production of dMSC-460 in a single-ensemble form at elevated temperatures, as shown by Scheme 1. The present study introduces new
avenues to synthesize single-ensemble CdSe dMSCs upon the addition of small molecules in the prenucleation stage of CdSe QDs and brings deeper insight into the existence of two individual but linked pathways to the production of CdSe QDs and dMSCs.
Figure 1 presents the optical properties of three samples extracted from three batches at 220 °C with a reaction period of 15 min at this temperature. The three batches address the s a m e r e a c t i o n s o f C d ( O A c )2, m y r i s t i c a c i d
(CH3(CH2)12COOH, HMA), and Se in ODE. The only
difference is in the application of vacuum and/or N2during the
two stages, when the temperature is increased from room temperature to 120 °C and when the temperature is kept at 120 °C for 2 h (Table S1). Afterward, the three batches are protected under a N2 atmosphere and the temperature is
increased. Figure S1-1 shows evolution of the optical properties of the three batch samples; from each batch, there are 10 samples extracted during the temperature increase from Scheme 1. Schematic Drawing To Illustrate the Effect of the
Addition of CH3COOH (HOAc) in the Prenucleation Stage
(at 120 °C) of the Reaction of Cd(MA)2and Se in ODE
a
aWithout addition (top), a mixture of MSCs and QDs is obtained.
With the addition (bottom), a single ensemble of dMSC-460 is obtained.
Figure 1.Optical absorption (dashed lines, left y axis) and emission spectra (solid lines, excited at 350 nm, right y axis) of the CdSe 220 °C/15 min samples (30 μL dispersed in 3.0 mL of toluene) from three reaction batches consisting of the same amounts of HMA, Cd(OAc)2, and Se powder. They were mixed at room temperature with the feed molar ratios of 8.8HMA (1.32 mmol) to 4Cd(OAc)2 (0.60 mmol) to 1Se (0.15 mmol) and a Se concentration of 30 mmol/kg in ODE. For the heating stage from room temperature to 120 °C and the 2 h stage at 120 °C, either a N2 atmosphere or vacuum is applied, as indicated. There appears to be a strong correlation between the vacuum and N2conditions and the resulting products produced.
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140 to 240 °C. Further details regarding the experiments can be found in theSupporting Information. It is noteworthy that a relatively large amount of HMA and a relatively large Se concentration are used to obtain the Figure 1 results, compared to literature reports about the similar reaction of Cd(OAc)2and HMA and Se in ODE.14,16,17The feed molar
ratio of HMA to Cd(OAc)2 is 2.2 to 1.0 instead of, for
example, 1.0 to 1.0. The Se concentration is 30 mmol/kg instead of 10 mmol/kg.
Interestingly, the optical properties of the resulting CdSe products from the three batches are significantly different. As shown byFigure 1, only when N2is used during the heating
stage to 120 °C and the constant temperature stage at 120 °C (Batch a) are two CdSe dMSC ensembles produced. One exhibits one sharp absorption doublet at 371/392 nm and an emission peak at 399 nm, while the other displays one sharp absorption doublet at 432/459 nm and an emission peak at 463 nm. These MSCs are referred to as 393 and dMSC-460, respectively. When vacuum is used during the heating stage and N2is applied in the constant temperature stage at
120 °C (batch b), a CdSe dMSC-460 ensemble is detected, with an absorption doublet at 431/454 nm and an emission peak at 459 nm. Figure S1-2 shows that dMSC-460 is 0-dimension with a size of ∼2 nm. When a vacuum is applied throughout the two stages (batch c), three emission peaks at 463, 503, and 567 nm are discernible. The relatively narrow emission peaking at 463 nm is associated with CdSe dMSC-460 exhibiting an absorption doublet at 430/454 nm, while the relatively broad emission peaking at 567 nm is related to the CdSe QDs exhibiting a relatively broad absorption peaking at ∼550 nm.
For the temperature increase stage to 120 °C from room temperature followed with the 2 h stage at 120 °C,Figure 1
demonstrates a clear correlation between the use of vacuum and/or N2 and the dMSCs and QDs produced at higher
temperatures. Such dependence, which is related to synthetic reproducibility, can be attributed to the reaction of Cd(OAc)2
+ 2HMA ⇒ Cd(MA)2 + 2HOAc; when the Cd source
compound Cd(OAc)2is dissolved in a reaction batch (around
80 °C), HOAc is produced. By a side note, the melting point of Cd(OAc)2 is ∼255 °C; the apparent disappearance of
Cd(OAc)2 at ∼80 °C for the three batches suggests that
similar amounts of HOAc are produced around this temper-ature. Thus, prior to the increase of temperature from 120 °C under a N2 atmosphere, the amount of HOAc in a reaction
depends on the use of vacuum and/or N2. From batch a to c, it
is reasonable that the amount of HOAc decreased. At the end of the two stages, it seems that there remains enough HOAc in batches a and b to produce CdSe dMSCs only, while both CdSe dMSCs and QDs are produced in batch c due to the presence of little HOAc. The presence of HOAc seems to suppress the nucleation and growth of QDs (after the duration stage at 120 °C). To test this hypothesis, 0.50 mmol of HOAc is added into a batch. Before the addition, this batch is identical toFigure 1batch c with a vacuum applied throughout the heating stage to 120 °C and the constant temperature stage at 120 °C. The addition is performed at the end of the two stages at 120 °C but under a N2atmosphere.
Figure 2 presents evolution of the optical properties of 10 samples extracted from the batch. Similar to those obtained from the Figure 1 batches, sampling is performed when the temperature is increased to 240 °C. Figure S2 shows the absorption and emission spectra of sample 9 (220 °C/15 min). Remarkably, no QDs but dMSCs are produced; furthermore, dMSC-460 is almost in a single-ensemble form at elevated temperatures (such as 240 °C). The evolution of dMSC-393 and dMSC-460 seems to be similar to that ofFigure 1batch a (Figure S1-1); dMSC-393 seems to develop slightly earlier than dMSC-460. For the batch associated with Figure 2, however, dMSC-460 becomes dominant at 220 °C (sample 8) and changes little when the temperature is increased to 240 °C (sample 10). ForFigure 1batch a, a mixture of both dMSC-393 and dMSC-460 is observed to coexist at 220 °C (sample 8); when the temperature is increased to 240 °C, the relative population of the two ensembles is almost constant. ForFigure 1batch b, only dMSC-460 appears; when the temperature is increased from 140 to 240 °C, its population increases. It is probable that the different evolution of 393 and dMSC-Figure 2.Evolution of the absorption (left) and emission (right, excited at 350 nm) spectra of the CdSe samples extracted (15 μL dispersed in 3.0 mL of toluene). The addition of HOAc (0.50 mmol) was performed under a N2atmosphere at 120 °C after a vacuum was applied throughout the heating stage to 120 °C and the constant temperature stage at 120 °C. After the addition, the reaction is kept at 120 °C for 15 min. Afterward, the reaction temperature is increased and samples are taken, similar to those ofFigure 1batches (Figure S1-1) at (1) 140 °C/0 min, (2) 160 °C/0 min, (3) 160 °C/15 min, (4) 180 °C/0 min, (5) 180 °C/15 min, (6) 200 °C/0 min, (7) 200 °C/15 min, (8) 220 °C/0 min, (9) 220 °C/15 min, and (10) 240 °C/0 min. Interestingly, no QDs are produced and one single ensemble of CdSe dMSC-460 is obtained at 220 and 240 °C (samples 8− 10).
460 in the four batches is due to the different amounts of HOAc presented in these batches.
From what we have seen, the presence of HOAc in the prenucleation stage plays apparently an important role both in the suppression of the nucleation and growth of QDs and in the formation of dMSCs. This observation leads to the hypothesis that if the amount of HOAc in the prenucleation stage is controlled, the reproducibility of the dMSC synthesis
would be improved. It is fairly straightforward that the addition of HOAc after vacuum (at the end of the two stages) allows much better control over the concentration of HOAc in reactions, such as seen by theFigure 2 batch compared with
Figure 1batches a and b. Toward this end, the synthesis with Cd(MA)2as a Cd precursor (made from CdO) is designed; for
the reactions studied (as shown byFigures 3−5 below), they have the same Cd to Se feed molar ratio of 4 to 1 and the Se Figure 3.Evolution of optical absorption (left) and emission (right, excited at 350 nm) of CdSe samples (15 μL dispersed in 3.0 mL of toluene) from three synthetic batches that have a feed molar ratio of 8.8HMA (1.32 mmol)−4CdO (0.60 mmol)−1Se (0.15 mmol) and a Se concentration of 30 mmol/kg in ODE. The three batches are evacuated during the temperature increase from room temperature to 120 °C and the 2 h duration at 120 °C. Afterward, a N2atmosphere is applied. (a) No addition is performed. (b) 5.00 mmol of HOAc is added and the temperature is kept at 120 °C for 15 min. (c) The temperature is cooled to 80 °C for the addition, and the temperature is kept for 15 min after addition. After the first sample is taken at 120 °C/15 min (a and b) or 80 °C/15 min (c), the reaction temperature is increased and samples are extracted. For batches a and b, sampling is performed at (2) 140 °C/15 min, (3) 160 °C/15 min, (4) 180 °C/15 min, (5) 200 °C/15 min, (6) 220 °C/15 min, (7) 240 °C/ 0 min, and (8) 240 °C/15 min. For Batch c, samples are taken at (2) 100 °C/15 min, (3) 120 °C/15 min, (4) 140 °C/15 min, (5) 160 °C/15 min, (6) 180 °C/15 min, (7) 200 °C/15 min, (8) 220 °C/15 min, (9) 240 °C/0 min, and (10) 240 °C/15 min. Evidently, the addition of HOAc in the IP suppresses the nucleation and growth of QDs and enables the evolution of a single ensemble of CdSe dMSC-460 at an elevated temperature (220 °C, trace 6 for a and b while trace 8 for c).
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concentration of 30 mmol/kg in ODE. Similar to what is done in conjunction with Figure 1 batch c, a vacuum is applied throughout the two stages. Afterward, the addition of HOAc or Zn(OAc)2is performed in the prenucleation stage under a N2
atmosphere, and the temperature is kept for 15 min before it is increased to 240 °C. Again, further details regarding the experiments can be found in theSupporting Information.
Figure 3presents evolution of optical absorption (left) and emission (right) of samples taken from three batches with Cd(MA)2 as a Cd precursor. For batch a, there is no HOAc
addition, and the result is presented as a background for batches b and c. The addition of HOAc (5.00 mmol) is performed for batch b at 120 °C and for batch c at 80 °C. For batch a, the nucleation and growth of QDs appears to occur around 140 °C (trace 2). During the temperature increase to 240 °C, the QDs grow in size (trace 8), exhibiting broad absorption and emission peaking at ∼590 and ∼610 nm, respectively. Meanwhile, it seems that at 160 °C (trace 3), a small amount of CdSe MSC-460 appears and its amount changes little afterward.
For batch b, interestingly, no QDs are produced even at 240 °C. The evolution of dMSC-393 and dMSC-460 takes place at 180 °C (trace 4). At 220 °C (trace 6), the former ensemble disappears, and the population of the latter increases. When the temperature is further increased to 240 °C from 220 °C, dMSC-460 changes little and seems to be quite stable thermally. Figure S3-1 shows our transmission electron
microscopy (TEM) and X-ray diffraction (XRD) study of the CdSe 220 °C/15 min sample. Similar to published results,14−17the as-synthesized CdSe species are 0-dimensional
with a diameter of ∼2 nm. Figure S3-2 presents photo-luminescence quantum yield characterization.
For batch c, again, no QDs are produced even at 240 °C, and a single ensemble of CdSe MSC-460 is also obtained at 220 °C (sample 8), obviously without the coproduction of QDs. Compared with batches a and b, there are two more samples extracted at 80 and 100 °C from this batch; they are samples 1 and 2, respectively. The evolution of dMSC-393 and dMSC-460 seems to take place at 160 °C (trace 5). At 220 °C (trace 8), 393 disappears, but the population of dMSC-460 increases. Afterward, dMSC-dMSC-460 changes little when the temperature is further increase to 240 °C. The growth patterns of the two dMSC ensembles are quite similar to those of batch b, suggesting high synthetic reproducibility.
The suppression of the nucleation and growth of QDs is evidently achieved by the addition of HOAc in the prenucleation stage, which also facilitates the production of a single ensemble of CdSe dMSC-460 at an elevated temper-ature (220 °C). This ensemble exhibits one sharp emission at ∼465 nm with little broad trap emission at longer wavelengths. The broad temperature range for small molecule addition is an obvious advantage, regarding the improvement of synthetic reproducibility of the CdSe dMSCs.
Figure 4.Evolution of optical absorption (left) and emission (right, excited at 350 nm) of CdSe samples (15 μL dispersed in 3.0 mL of toluene) from two synthetic batches similar to those ofFigure 3, with a feed molar ratio of 8.8HMA (1.32 mmol)−4CdO (0.60 mmol)−1Se (0.15 mmol) and a Se concentration of 30 mmol/kg in ODE. The addition of Zn(OAc)2(0.13 mmol (a) or 0.25 mmol (b)) is performed at 120 °C. After 15 min, the first sample is taken at 120 °C/15, and the reaction temperature is increased with sampling at (2) 140 °C/15 min, (3) 160 °C/15 min, (4) 180 °C/15 min, (5) 200 °C/15 min, (6) 220 °C/15 min, (7) 240 °C/0 min, and (8) 240 °C/15 min. Clearly, with the addition of Zn(OAc)2in the IP, the nucleation and growth of QDs is suppressed as well.
Figure 4 presents evolution of the optical absorption (left) and emission (right) properties of two batch samples, with the addition of Zn(OAc)2. The two batches are the same asFigure
3 batch a; at the end of the two stages at 120 °C, a N2
atmosphere is applied and an addition of 0.13 mmol (a) or 0.25 mmol (b) is performed. After another 15 min at 120 °C, the first sample is taken. Then, the reaction temperature is increased with samples extracted, similar toFigures 3a and3b, at (2) 140 °C/15 min, (3) 160 °C/15 min, (4) 180 °C/15 min, (5) 200 °C/15 min, (6) 220 °C/15 min, (7) 240 °C/0 min, and (8) 240 °C/15 min. Obviously, there are no QDs produced, and CdSe dMSC-393 does not seem to evolve either. The evolution of CdSe dMSC-460 occurs at 160 °C (trace 3) for batch a and at 140 °C (trace 2) for batch b. The population of dMSC-460 keeps increasing when the temper-ature is increased to 240 °C. Figure S4 presents the optical properties of another batch samples, with the same addition of Zn(OAc)2but with a larger amount of 2.50 mmol.
Similar to the HOAc addition in the prenucleation stage, the addition of Zn(OAc)2 in the prenucleation stage also
articulately suppresses the nucleation and growth of CdSe QDs and enables the development of CdSe dMSCs. For the production of CdSe dMSCs without the presence of QDs, the addition of HOAc or an acetate salt in the prenucleation stage is a practical approach. Moreover, for the production of a single ensemble of CdSe dMSC-460 at an elevated temper-ature (220 °C) to exhibit one emission peak at 465 nm with little broad trap emission, the use of HOAc seems to be more efficient than that of Zn(OAc)2. At the same time, the use of
Zn(OAc)2 might introduce complication (especially at high
temperatures due to the presence of another cation in a reaction).
For the approach developed with good synthetic reprodu-cibility upon the addition of HOAc,Figure 5presents further that the amount (0.50−10.00 mmol) of HOAc added at 120 °C does not play a critical role on the production of the single ensemble of CdSe dMSC-460 at 220 °C. Figure 5 shows evolution of the optical absorption (left) and emission (right) of the samples from two reaction batches. The two batches are similar to Figure 3 batch b, with the addition of HOAc performed at 120 °C but with different amounts of (a) 0.50 and (b) 10.00 mmol. Figure S5-1 presents evolution of the optical properties of the samples from a batch with the addition of HOAc of 0.25 mmol. Regarding the synthetic reproducibility of CdSe MSC-460 in a single ensemble form, which exhibits one sharp emission at 465 nm without broad trap emission, the optimal amount range of HOAc seems to be quite broad, which can span from 0.50 to 10.00 mmol.
The present study explores a nonphosphorus containing approach to CdSe MSC-460 with a sharp emission peaking at 465 nm and with little broad trap emission at longer wavelengths. Intriguingly, when SeTOP is used as a Se precursor, as shown by Figure S5-2, the addition of HOAc (0.5−5.00 mmol) suppresses the nucleation and growth of QDs, and a single ensemble of CdSe dMSC-460 is produced at 220 °C also. However, this ensemble exhibits significant trap emission at wavelengths longer than 465 nm. The use of SeTOP as a Se precursor seems to affect the emission properties of resulting CdSe dMSCs; this is similar to that reported previously, where Cd(OAc)2was used together with
Figure 5.Evolution of absorption (left) and emission (right, excited at 350 nm) of the CdSe samples (15 μL dispersed in 3.0 mL of toluene) extracted from two reactions, which are similar toFigure 3batch b, but with the addition of HOAc of 0.50 (a) and 10.00 mmol (b) added at 120 °C. The sampling is performed at (1) 120 °C/15, (2) 140 °C/15 min, (3) 160 °C/15 min, (4) 180 °C/15 min, (5) 200 °C/15 min, (6) 220 °C/15 min, (7) 240 °C/0 min, (8) 240 °C/15 min, and (9) 240 °C/30 min. It seems that the optimal amount HOAc added in the IP is as broad as from 0.50 to 10.00 mmol, which produces CdSe dMSC-460 in a single ensemble form.
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HMA to react with SeTOP, but without the addition of HOAc.14
In conclusion, we have demonstrated that the presence of molecules containing the CH3COO− group in the
prenuclea-tion stage of CdSe QDs is able to effectively suppress the nucleation and growth of QDs. We have explored systemati-cally the addition of HOAc and Zn(OAc)2in the prenucleation
stage (at 120 °C) of CdSe QDs, with Cd(MA)2 as a Cd
precursor (made from CdO) to react with Se powder in ODE. The Cd to Se feed molar ratio is fixed at 4 to 1 and the Se concentration is 30 mmol/kg. Without the addition, the nucleation and growth of QDs seems to occur around 140 °C. With the addition, the nucleation and growth of QDs does not take place, even at 240 °C. Moreover, CdSe dMSC-460 evolves at 220 °C as a single ensemble exhibiting a sharp emission peak at ∼465 nm without broad trap emission at longer wave-lengths. Importantly, the temperature at which the addition is performed and the added amount do not seem to be critical, suggesting that the approach has good synthetic reproduci-bility. Experimentally, the addition of small molecules in the prenucleation stage suppresses the nucleation and growth of QDs and enables the formation of CdSe dMSCs. We hypothesize that the added molecule interacts with the monomer, fragment, and precursor compound produced in the prenucleation stage,1,29as shown byScheme 1. The present study brings insights into the two pathway model to CdSe QDs and dMSCs;1,8,11via the addition of small molecules within the prenucleation stage, only dMSCs are synthesized in a single ensemble form without the coproduction of QDs. The findings should assist the application development based on the species characterized by similar sharp absorption doublets.30−33 We
also anticipate that the present results will encourage a re-examination of the published results,14−17,26−28,34−37and will
motivate theoretical efforts to narrow the knowledge gap regarding the structure−property relationship of sMSCs and dMSCs.
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ASSOCIATED CONTENT*
S Supporting InformationThe Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jp-clett.8b03016.
Experimental details including synthesis and character-ization with optical absorption, emission, TEM, and XRD (PDF)
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AUTHOR INFORMATIONCorresponding Authors
*S.H. E-mail:shuohan@scu.edu.cn. *K.Y. E-mail: kuiyu@scu.edu.cn. ORCID
Hongsong Fan:0000-0003-3812-9208
Shuo Han: 0000-0003-0880-1833
Kui Yu: 0000-0003-0349-2680
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTSK.Y. thanks National Natural Science Foundation of China (NSFC) 21573155 and 21773162, the State Key Laboratory of Polymer Materials Engineering of Sichuan University (Grant
No. sklpme2018-2-08), and Open Project of Key State Laboratory for Supramolecular Structures and Materials of Jilin University for SKLSSM 201830. S.H. thanks Sichuan University for postdoctoral fellowship financial support of 2017SCU12012. We thank Dr. Shanling Wang (Analytical & Testing Center, Sichuan University) for TEM and Prof. J. You for his quantum yield measurements.
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The Journal of Physical Chemistry Letters Letter
DOI:10.1021/acs.jpclett.8b03016
J. Phys. Chem. Lett. 2018, 9, 6356−6363 6363
