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Multifunctional Octamethyltetrasila[2.2]cyclophanes: Conformational Variations, Circularly Polarized Luminescence, and Organic Electroluminescence

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posted on 2017-07-21, 00:00 authored by Masaki Shimada, Yoshinori Yamanoi, Tatsuhiko Ohto, Song-Toan Pham, Ryo Yamada, Hirokazu Tada, Kenichiro Omoto, Shohei Tashiro, Mitsuhiko Shionoya, Mineyuki Hattori, Keiko Jimura, Shigenobu Hayashi, Hikaru Koike, Munetaka Iwamura, Koichi Nozaki, Hiroshi Nishihara
Both symmetrical and unsymmetrical cyclophanes containing disilane units, tetrasila[2.2]­cyclophanes 19, were synthesized. The syn and anti conformations and the kinetics of inversion between two anti-isomers were investigated by X-ray diffraction and variable-temperature NMR analysis, respectively. The flipping motion of two aromatic rings was affected by the bulkiness of the aromatic moiety (1 vs 6), the phase (solid vs solution), and the inclusion by host molecules (1 vs 1⊂[Ag2L]2+). The photophysical, electro­chemical, and structural properties of the compounds were thoroughly investigated. Unsymmetrical tetrasila[2.2]­cyclophanes 58 displayed blue–green emission arising from intramolecular charge transfer. Compound 6 emitted a brilliant green light in the solid state under 365 nm irradiation and showed a higher fluorescence quantum yield in the solid state (Φ = 0.49) than in solution (Φ = 0.05). We also obtained planar chiral tetrasila[2.2]­cyclophane 9, which showed interesting chiroptical properties, such as a circularly polarized luminescence (CPL) with a dissymmetry factor of |glum| = ca. 2 × 10–3 at 500 nm. Moreover, an organic green light-emitting diode that showed a maximum external quantum efficiency (ηext) of ca. 0.4% was fabricated by doping 4,4′-bis­(2,2′-diphenylvinyl)-1,1′-biphenyl with 6.

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