Enhanced Luminescence of a σ–π-Conjugated Disilane-Bridged Donor–Acceptor Macrocycle through Conformational Restriction

Abstract Disilane-bridged arenes are a useful class of σ–π-conjugated molecules in which Si–Si σ bonds interact with adjacent π-conjugated systems. We previously reported a linear D–A–D-type disilane-bridged aromatic molecule containing a thienopyrazine unit, l -Th2Thpz, which exhibited long-wavelength emission in solution (D: donor and A: acceptor). Herein, we designed and synthesized a disilane-bridged trimeric thiophenophane, c -Th2Thpz, to investigate how macrocyclization affects the electronic structure and luminescence properties of disilane-bridged D–A–D molecules. Single-crystal X-ray diffraction analysis revealed that c -Th2Thpz possesses a cyclic trimeric structure composed of three heteroaromatic rings and three Si–Si bonds. c -Th2Thpz exhibited an enhanced photoluminescence quantum yield compared with the linear analogue l -Th2Thpz, indicating that donor–acceptor-type electronic interactions through the disilane bridges are retained in the macrocyclic framework. Notably, the photoluminescence quantum yield of c -Th2Thpz increased from 0.09 in CH2Cl2 to 0.24 in the crystalline state, which is substantially higher than that of the linear analogue l -Th2Thpz in CH2Cl2 (ΦF = 0.02). This enhancement is mainly attributed to suppression of nonradiative decay in the structurally restricted macrocycle and in the crystalline state. These results demonstrate that macrocyclization is an effective strategy for enhancing luminescence while maintaining σ–π-conjugation-mediated D–A interactions in disilane-bridged luminophores.