Regulating the excited state chirality to fabricate high-performance-solid-state circularly polarized luminescence materials

Developing solid-state materials and greatly improving the luminescence dissymmetry factors (g(lum)) are the key issues for the future oriented practical application in the field of circularly polarized luminescence (CPL). However, most of the solid-state CPL-active materials suffer from aggregation caused emission quenching and relatively small g(lum) values, which intensively restrict the development and application. In this work, high-performance CPL-active solid-state materials were achieved by regulating the excited state chirality of a series of bi-pyrene based chiral emitters. Due to the reversible mechanochromic luminescence under external stimuli, their excited state chirality can also be switched. It was found that the pristine amorphous powder possessed weak but obvious chiroptical properties because of the inherently chiral structures. Mechanical grinding could switch the fluorescence color and eliminate the CPL activity. Subsequently, by carrying out solvent fumigation, instant crystallization with well-defined microcrystal formation occurred, which could activate the CPL emission. Due to the chiral supramolecular arrangement of chromophores in the crystalline state, the resulting excimer emission in microcrystals showed chirality amplification not only in the excited state but also in the ground state. These findings not only provide a new method to fabricate high-performance CPL-active solid-state materials, but also clarify the chirality origin of pyrene-excimer-based chiral luminophores in various states which showed the importance of CPL as a probe of excited state chirality.