ZnS quantum dots have been shown to be synthesized from zinc oleate and thiourea in organic solvents at high temperatures (≥240°C).1 Zinc oleate is an excellent zinc source because the decomposition yields Zn(II) metal and oleate, an excellent capping agent. Disubstituted thioureas have been used as a sulfur source, where the strength of the carbon–sulfur bond can be tuned by modifying the substituent R-groups (R1-R4).1 Diaryl thioureas convert faster than dialkyl ones, and mixed N-alkyl-N’-aryl thioureas have intermediate rates of conversion. The rates can be tuned by the addition of electron-withdrawing groups on aromatic rings.1 The final ZnS nanocrystal size synthesized from disubstituted thioureas is independent of the temperature of the reaction.2 Herein, I have synthesized four disubstituted thiourea precursors and tested for their ability to decompose at temperatures lower than 200 °C. Each thiourea falls into a specific category: symmetrical diaryl, unsymmetrical diaryl, symmetrical dialkyl, and unsymmetrical dialkyl. This categorization was used to study how the structure influences the rate of conversion and temperatures of decomposition.
References
1 Hendricks, M. P.; Campos, M. P.; Cleveland, G. T.; Plante, I. J.-L.; Owen, J. S. A tunable library of substituted thiourea precursors to metal sulfide nanocrystals. Science. 2015, 348, 1226-1230.
2 Bennett, E.; Greenberg, M. W.; Jordan, A. J.; Hamachi, L. S.; Banerjee, S.; Billinge, S. J. L.; Owen, J. S. Size Dependent Optical Properties and Structure of ZnS Nanocrystals Prepared from a Library of Thioureas. Chem. Mater. 2022, 34, 706-717.