Copper Selenides via Anion Exchange versus Direct Growth – The Role of Diorganyl Diselenides

Anion exchange is a powerful tool for postsynthetic transformation of nanoparticles that can be coupled with other transformations to create nanostructures unachievable by direct growth. Previous work implicated long-chain dialkyl diselenides as drivers of Se2– anion exchange on Cu2–xS, but it lacked mechanistic details. Here, we examined the reactivity trends of diphenyl, didodecyl, and dibenzyl diselenides as drivers of anion exchange to create metastable copper sulfur selenide alloys. We contrasted these reactivity trends with those of direct synthesis of copper selenide nanoparticles, demonstrating mechanistic orthogonalities between these pathways. Dialkyl diselenides were the only species that induced anion exchange. We rationalized the different reaction outcomes using thermal decomposition measurements together with MD simulations using a ReaxFF force field (trained against DFT data). Dialkyl diselenides were shown to release H2Se, which appears to be critical for achieving Se2– anion exchange. This demonstrates the utility of computationally inexpensive atomistic-scale simulations methods like ReaxFF in the rational design of nanoparticle syntheses. Using this insight, the dialkyl diselenides were identified as a new class of selenium exchange reagents based on initial MD simulations of H2Se release. This work provides mechanistic understanding of nanoparticle anion exchange and insights into decomposition processes crucial to use of diorganyl diselenides in nanoparticle synthesis.

阴离子交换（anion exchange）是实现纳米颗粒后合成转化的高效手段，可与其他转化策略联用，制备出直接生长无法获得的纳米结构。此前研究虽指出长链二烷基二硒醚可作为Cu₂₋ₓS上Se₂⁻阴离子交换的驱动剂，但未阐明相关机理细节。本工作选取二苯基二硒醚、双十二烷基二硒醚与二苄基二硒醚作为Se₂⁻阴离子交换的驱动剂，探究其反应活性规律，成功制备得到亚稳态铜硫硒固溶体。我们将该阴离子交换反应的活性规律与直接合成硒化铜纳米颗粒的规律进行对比，证实两条反应路径间存在机理正交性。仅二烷基二硒醚可诱导该阴离子交换反应。我们结合热分解测试与基于密度泛函理论（DFT）数据训练的ReaxFF反应力场的分子动力学（MD, Molecular Dynamics）模拟，对不同反应结果进行了合理化阐释。研究表明，二烷基二硒醚会释放硒化氢（H₂Se），而该物质对实现Se₂⁻阴离子交换过程至关重要。本研究证明了ReaxFF等计算成本较低的原子级模拟方法，可用于合理设计纳米颗粒合成路线。基于H₂Se释放的初步分子动力学模拟结果，我们将二烷基二硒醚鉴定为一类新型硒交换试剂。本工作阐明了纳米颗粒阴离子交换的反应机理，并揭示了二有机二硒醚应用于纳米颗粒合成时的关键分解过程。