Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2010 Dec 29;132(51):18206-13. doi: 10.1021/ja106777j. Epub 2010 Dec 3.
The kinetics of cadmium selenide (CdSe) nanocrystal formation was studied using UV-visible absorption spectroscopy integrated with an automated, high-throughput synthesis platform. Reaction of anhydrous cadmium octadecylphosphonate (Cd-ODPA) with alkylphosphine selenides (1, tri-n-octylphosphine selenide; 2, di-n-butylphenylphosphine selenide; 3, n-butyldiphenylphosphine selenide) in recrystallized tri-n-octylphosphine oxide was monitored by following the absorbance of CdSe at λ = 350 nm, where the extinction coefficient is independent of size, and the disappearance of the selenium precursor using {(1)H}(31)P NMR spectroscopy. Our results indicate that precursor conversion limits the rate of nanocrystal nucleation and growth. The initial precursor conversion rate (Q(o)) depends linearly on [1] (Q(o)(1) = 3.0-36 μM/s) and decreases as the number of aryl groups bound to phosphorus increases (1 > 2 > 3). Changes to Q(o) influence the final number of nanocrystals and thus control particle size. Using similar methods, we show that changing [ODPA] has a negligible influence on precursor reactivity while increasing the growth rate of nuclei, thereby decreasing the final number of nanocrystals. These results are interpreted in light of a mechanism where the precursors react in an irreversible step that supplies the reaction medium with a solute form of the semiconductor.
采用紫外-可见吸收光谱法，并结合自动化高通量合成平台，研究了碲化镉（CdSe）纳米晶体的形成动力学。无水十八烷基磷酸镉（Cd-ODPA）与烷基膦硒化物（1、三正辛基膦硒化物；2、二正丁基苯基膦硒化物；3、正丁基二苯基膦硒化物）在重结晶的三正辛基氧化膦中的反应，通过监测 CdSe 在 λ = 350nm 处的吸光度来跟踪，其中消光系数与尺寸无关，并且使用 {(1)H}(31)P NMR 光谱法跟踪硒前体的消失。我们的结果表明，前体转化率限制了纳米晶成核和生长的速率。初始前体转化率（Q(o)）与 [1] 呈线性关系（Q(o)(1) = 3.0-36 μM/s），并且随着与磷结合的芳基数量的增加而降低（1 > 2 > 3）。Q(o) 的变化会影响最终纳米晶体的数量，从而控制颗粒尺寸。使用类似的方法，我们表明改变 [ODPA] 对前体反应性的影响可以忽略不计，同时增加了核的生长速率，从而减少了最终纳米晶体的数量。这些结果根据一种机制进行了解释，在前体反应中不可逆步骤提供了半导体的溶质形式的反应介质。
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