Synthesis of Optically Active pi-Conjugated Molecules Based on Planar Chiral [2.2]ParacycloPhane

We have focused on planar chirality of [2.2] paracyclophanes with substituent(s). In addition, we have developed their practical optical resolution methods by mainly diastereomer methods and synthetic routes to planar chiral [2.2] paracyclophane compounds. The obtained optically active disubstituted and tetrasubstituted [2.2] paracyclophanes have been utilized for chiral building blocks to produce a wide variety of optically active pi-stacked molecules including polymers. The planar chiral [2.2] paracyclophane-based pi-stacked molecules exhibited circularly polarized luminescence (CPL) with a large dissymmetry factor (g(lum) value) derived from the optically active second-ordered structures, such as V-, X-, triangle-, one-handed double helical structures, in the excited state. It was the first example on the application of the planar chirality of [2.2] paracyclophane to the field of polymer chemistry as well as materials chemistry. pi-Electron systems constructed by [2.2] paracyclophane emit photoluminescence (PL) depending on the conjugation length of the stacked pi-electron system. When conjugation length of a stacked pi-electron system is extended, the molecule exhibits monomeric PL rather than excimer-like PL despite the stacked structure in proximity. Even if the several tens of pi-electron systems are stacked, PL profiles such as PL life time and quantum efficiency are identical. pi-Conjugation lengths of monomeric pi-electron systems in this article are sufficiently extended; thus, the [2.2] paracyclophane-based pi-stacked molecules in this article emit brightly with good PL quantum efficiencies. Moreover, the luminescence is CPL with the large g(lum) value in organic molecules. It is quite difficult to achieve CPL with high brightness, high PL efficiency, and large g(lum) value by using other scaffolds; therefore, planar chiral [2.2] paracyclophane is the ideal scaffold to be an excellent CPL emitters.