2020 年 78 巻 2 号 p. 148-157
Recently, the development of optically active luminophores that can emit circularly polarized luminescence (CPL) with high functionalities, such as a high dissymmetry factor (gCPL) and a high quantum yield (ΦF), has attracted attention in the field of chiroptical organic materials. However, the design of chiral luminophores that bear CPL tuning, switching, memory, and elimination has been hampered by the fact that the relationship between the structure of the photoexcited state and the chirality of the photoexcited state of chiral luminophores is not yet fully understood.
Typically, a pair of enantiomeric organic fluorophores is indispensable for the emission of opposite CPL. Unfortunately, it is not always easy to prepare both enantiomers. Hence, it is necessary to find an alternative, non-classical route for controlling the sign of CPL in chiral fluorophores without the use of a fluorophore that has opposite chirality. In this paper, we report a non-classical approach for controlling the sign, wavelength, and intensity of the CPL. We report that in binaphthyl-derived fluorophores having the same axial chirality, the CPL sign can be controlled by 1) altering the dihedral angle of the axially chiral binaphthyl units, 2) tuning the linkers between the binaphthyl and fluorescent units, 3) selecting the bonding position of the fluorescent unit, 4) taking advantage of the neighboring effect between the fluorescent units, and 5) selecting appropriate organic host matrices. These non-classical methods may be useful for the development of novel chiral organic fluorophores, particularly when one of the enantiomers is easily accessible in nature. This non-classical approach to control the sign of CPL is instrumental for the development of novel chiral fluorescent systems.