Metallomesogen Templates for Shape Control of Metal Selenide Nanocrystals

Metal alkanethiolates are organometallic single-source precursors that have been used to synthesize metal sulfide nanocrystals (NCs) from thermal decomposition reactions. Ag and Cu alkanethiolates are remarkable because they adopt lamellar bilayer nanostructures that give rise to mesogenic behavior akin to that of thermotropic liquid crystals. Such metallomesogen precursors have been demonstrated to template the nucleation and growth of highly anisotropic NC morphologies. In this work, we synthesize novel metallomesogen compounds, namely, CuSeC<sub>12</sub>H<sub>25</sub> and AgSeC<sub>12</sub>H<sub>25</sub>, to target shaped metal selenide NCs. We show that these compounds adopt lamellar bilayer structures and undergo mesogenic transitions at elevated temperatures. We find that structural disparities between the CuSeC<sub>12</sub>H<sub>25</sub> and AgSeC<sub>12</sub>H<sub>25</sub> mesophases lead to the formation of distinct two- and one-dimensional NC morphologies, respectively. Moreover, both compounds exhibit an isotropic phase that produces either nanospheres or irregularly shaped particles. By exploiting the morphology-directing capability of the mesogenic regime, we detail the synthesis of ultrathin Cu<sub>2</sub>Se nanoribbons, Ag<sub>2</sub>Se nanorods, and AgCuSe nanospheres. This work demonstrates that metallomesogens can serve as a novel class of NC precursors with the ability to access highly anisotropic morphologies and tailored compositions.