To prepare a 1.1 mmol/mL OLA-HX precursor solution, 10 mL of oleylamine (OAm) was placed in a 25-mL three-neck flask and either 1 mL of concentrated hydrochloric acid (HCl(aq.)) or 1.28 mL of concentrated hydrobromic acid (HBr(aq.)) was added slowly. Subsequently, the solidified reaction mixture was heated at 120 °C under nitrogen atmosphere for 2 h. The reaction temperature was then increased to 150 °C for 30 min and afterwards allowed to cool to room temperature. The mixture was kept in a glovebox and heated to 80 °C before injection.