Department of Chemistry, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.
J Am Chem Soc. 2014 Feb 5;136(5):1968-75. doi: 10.1021/ja4110182. Epub 2014 Jan 22.
This paper reports a detailed mechanistic study of the effect of alkylamine on the synthesis of CdSe nanocrystals. Alkylamines are one of the most important additives for the synthesis of colloidal semiconductor nanocrystals. However, their effect on the monomer production as well as nanocrystal nucleation and growth are not well understood, as indicted by inconsistent and contradictory conclusions in the literature. We found that alkylamines slow down the reaction between cadmium oleate and trialkyl phosphine selenide by binding to cadmium and preventing the activation of trialkyl phosphine selenide. A linear correlation was observed between the observed reaction rate constant and the (31)P NMR chemical shift or (1)J(P-Se) of phosphine selenide. In the presence of alkylamine, an alkylaminophosphonium intermediate was observed. Mechanistic study suggests that the cleavage of P═Se bond is through nucleophilic attack by carboxylate instead of alkylamine. Interestingly, although alkylamines decrease the rate of monomer production, it increases the rate of CdSe nanocrystal growth. Although seemingly contradictory, this is due to a drastic decrease in the nanocrystal nucleation events in the presence of alkylamines. As a result, each nucleus is fed with more monomers and grows faster in the presence of alkylamine than in its absence.
本文报道了烷基胺对 CdSe 纳米晶体合成影响的详细机理研究。烷基胺是胶体半导体纳米晶体合成中最重要的添加剂之一。然而，它们对单体生成以及纳米晶成核和生长的影响尚未得到很好的理解，这反映在文献中存在不一致和矛盾的结论。我们发现，烷基胺通过与镉结合并阻止三烷基膦硒化物的活化，从而减缓了油酸镉与三烷基膦硒化物之间的反应。观察到的反应速率常数与（31）P NMR 化学位移或膦硒化物的（1）J（P-Se）之间存在线性相关性。在烷基胺存在下，观察到了烷基氨膦盐中间体。机理研究表明，P═Se 键的断裂是通过羧酸盐而不是烷基胺的亲核攻击进行的。有趣的是，尽管烷基胺降低了单体生成的速率，但它增加了 CdSe 纳米晶生长的速率。虽然看似矛盾，但这是由于烷基胺存在下纳米晶成核事件急剧减少所致。结果，每个核在烷基胺存在下比在其不存在时接收更多的单体并生长得更快。
