**2. Experimental**

The starting material, Cd(SC6H4Me-4)2, was prepared according to reference [12]. The product is white precipitate with yield up to 75% in weight. The typical target cadmium chalcogenides compound, denoted as NCYU-6, was prepared as follows. Cd(SC6H4Me-4)2 (100 mg), thiourea powder (50 mg, 99%, Alfa Aesar), tettrahydrofuran (4.5 mL, 99.9%, Pharmco), selenium powder (10 mg, 99.5%, Acros), and de-ionized H2O (2.1 mL) were dissolved in a 33 mL stainless steel autoclave with lined Teflon. The reactants were stirred for 60 min before the sealed vessel was heated at 85°C for 28 days. When the reaction is finished, the autoclave was cooled down to room temperature for several hours in atmosphere. The product was then washed by a mixture of ethanol and methanol several times to remove any residue on crystals. The crystal is pale yellow and is stable in air, water, or polar solvents for several months. The yield is generally below 30% in weight. It is worthy to note that the weight ratio between Se and S should be carried out very precisely. If the derivation of Se/S weight ratio is higher than ±5%, no crystal could be found in the final product. For the experimental purpose, a yellow crystal, NCYU-7, was prepared via the same route as that of NCYU-6, except the addition of selenium powder in the reactants. The yield of NCYU-7 is ~50% in weight.
