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

Both
symmetrical and unsymmetrical cyclophanes containing disilane
units, tetrasila[2.2]­cyclophanes 1–9, 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 5–8 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.

本研究成功合成了含二硅烷（disilane）结构单元的对称与非对称环蕃（cyclophanes）类化合物，即四硅[2.2]环蕃1~9。分别通过X射线衍射（X-ray diffraction）与变温核磁共振（variable-temperature NMR）分析，对该类化合物的顺式（syn）、反式（anti）构象，以及两种反式异构体间的反转动力学进行了系统研究。两个芳香环的翻转运动受多重因素调控：芳基取代基的空间位阻（化合物1与6对比）、存在相态（固态与溶液态对比）以及主体分子的包合作用（化合物1与1⊂[Ag₂L]²⁺包合物对比）。研究团队对该系列化合物的光物理、电化学与结构性质开展了全面表征。非对称型四硅[2.2]环蕃5~8呈现出源于分子内电荷转移（intramolecular charge transfer）的蓝绿色荧光发射。化合物6在365 nm紫外辐照下于固态时可发出明亮绿光，其固态荧光量子产率（fluorescence quantum yield，Φ=0.49）显著高于溶液态（Φ=0.05）。本研究还获得了平面手性（planar chiral）四硅[2.2]环蕃9，该化合物展现出颇具研究价值的手性光学性质（chiroptical properties）：在500 nm波长处，其圆偏振发光（CPL, circularly polarized luminescence）的不对称因子（dissymmetry factor）|g_lum|约为2×10⁻³。此外，以化合物6掺杂4,4'-二(2,2'-二苯乙烯基)-1,1'-联苯作为发光活性层，制备得到有机绿光二极管，其最大外量子效率（external quantum efficiency, ηext）约为0.4%。