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 - 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 - were coordinated with Cu(I) in an conformation relative to the Si-Si σ bond, whereas those of were coordinated with Cu(I) in a 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. - exhibited blue-green emission (λ: 476-494 nm), and exhibited green-yellow emission (λ: 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 state at 293 K and phosphorescence from the 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 ( > 80%), although they did not show emission in dehydrated THF.