Structures and Optical Properties of Tris(trimethylsilyl)silylated Oligothiophene Derivatives

The structures and optical properties of tris­(trimethylsilyl)­silylated oligothiophenes were examined by spectroscopies, theoretical calculations, and single-crystal X-ray measurements. Bathochromic shift from the original oligothiophenes was observed in the tris­(trimethylsilyl)­silylated ones, confirming the σ–π conjugation between Si–Si σ bonds and π-orbital. 5,5′-Bis­(tris­(trimethylsilyl)­silyl)-2,2′-bithiophene (<b>Si-T</b>_<b>2</b>) showed the highest fluorescence quantum yield (Φ_F) both in solution (0.67, excited at 350 nm) and the solid state (0.74, excited at 371 nm). The introduction of tris­(trimethylsilyl)­silyl groups led to the small nonradiative rate constant of <b>Si-T</b>_<b>2</b>, resulting in the high Φ_F in the solution state. <b>Si-T</b>_<b>2</b> also exhibited effective σ–π conjugation and poor molecular interaction, which reflected its high Φ_F in the solid state. On the contrary, lower Φ_F (0.13, excited at 331 nm) in the solid state was observed in the longest oligothiophene examined, 5,5‴-bis­(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)­trisilan-2-yl)-2,2′:5′,2″:5″,2‴-quaterthiophene (<b>Si-T</b>_<b>4</b>). Single-crystal X-ray measurement clarified that this compound adopted a zigzag packing structure and a rare <i>syn-anti-syn</i> conformation, which led to the poor σ–π conjugation and the decrease of π-orbital overlap in the solid state