Structural and Photophysical Differences in Crystalline Trigonal Planar Copper Iodide Complexes with 1,2-Bis(methylpyridin-2-yl)disilane Ligands

We synthesized trigonal planar Cu(I) iodide complexes with 1,2-bis(methylpyridin-2-yl)disilane ligands <b>L1</b>-<b>L4</b> and investigated how the substitution position of the methyl group on the pyridine ring in σ-π conjugation affects their structure and physical properties. The structures were characterized by NMR, elemental analysis, and single-crystal X-ray diffraction. In the crystalline state, the methylpyridyl groups of <b>CuIL1</b>-<b>CuIL3</b> were coordinated with Cu(I) in an <i>anticlinal</i> conformation relative to the Si-Si σ bond, whereas those of <b>CuIL4</b> were coordinated with Cu(I) in a <i>synperiplanar</i> conformation relative to the Si-Si σ bond. The conformational difference in the crystalline state was influenced by the N-Cu-N bite angle and the emission wavelength. <b>CuIL1</b>-<b>CuIL3</b> exhibited blue-green emission (λ_em: 476-494 nm), and <b>CuIL4</b> exhibited green-yellow emission (λ_em: 512 nm) with high emission quantum yields (Φ: 0.59-0.86) in the crystalline state at 293 K. These Cu(I) complexes exhibited thermally activated delayed fluorescence from the <i>S</i>₁ state at 293 K and phosphorescence from the <i>T</i>₁ state at 77 K in the crystalline state. The optical properties in the crystalline state were discussed by DFT and TD-DFT calculations. These complexes also displayed aggregation-induced emission in THF-water solution (<i>f</i>_w > 80%), although they did not show emission in dehydrated THF.