Figure S1. Intensity variation upon addition of PMS to [Cu₈I₈(PMS)₄(MeCN)₂] _n (1), showing maximum intensity at formation of Cu₄I₄(PMS)₄ (2).

Figure S2. Powder X‐ray diffraction patterns of complexes 1 and 2, showing crystal transformation between complexes 1 and 2.

Figure S3. Solid‐state excitation spectra of complex 2 at 293 K and 77 K. Broken parts are ghost peaks which correspond to halves of emission wavelengths. Arrows indicate approximate locations coupled with emission wavelengths.

Figure S4. Solid‐state emission spectra of complex 2 with λ_ex = 325 nm showing intensity increase of center band and concomitant decreases of higher and lower energy bands at 77 K.

Figure S5. Emission spectra of CuI, 2, and 2 with a small amount of CuI at room temperature (λ_ex = 355 nm). This shows that peaks at a range of 400–475 nm could be originated from samples or contaminated CuI since thioether complexes lose ligand molecules owing to weak CuS bonds, leaving CuI.

Figure S6. TGA‐DTA Curves of complexes 1 and 2. In the TGA curve of complex 1, both acetonitrile and PMS ligand molecules were totally decoordinated from the complex up to around 160°C as indicated by weight loss 25.5% (calculated 24.4%). Similarly, in the TGA curve of complex 2, PMS ligands were totally detached from the complex after around 150°C, as indicated by weight loss 32.8% (calculated 34.9%). After 500°C, further decomposition of residual CuI occurs.

Figure S7. IR spectra of complexes 1 and 2. Two peaks near an arrow display CN stretching vibrations of bound acetonitrile molecules.

Table S1. Crystal data and structure refinement for complex 1 at 173 K.

Table S2. Selected bond lengths [Å] and angles [°] for complex 1 at 173 K.

Table S3. Crystal data and structure refinement for complex 2 at 173 K.

Table S4. Selected bond lengths [Å] and angles [°] for complex 2 at 173 K.

Table S5. Crystal data and structure refinement for complex 3 at 173 K.

Table S6. Selected bond lengths [Å] and angles [°] for complex 3 at 173 K.

Table S7. Selected bond lengths [Å] for complex 2 at173 K and 296 K.