Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule

A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90 degrees exhibit (-)- and (+)-CPL, respectively.

Automated summary

A series of axially chiral binaphthyls and quaternaphthyls with alternating aromatic fluorophores were synthesized using a divergent method, leading to the formation of unidirectionally twisted exciplex exhibiting circularly polarized luminescence (CPL). These compounds represent the first examples of monomolecular exciplex CPL dyes and the versatile synthesis method also improved fluorescence intensity. The study confirmed that the excimer chirality rule can be applied to exciplex dyes, with left- and right-handed exciplexes showing (-)- and (+)-CPL, respectively, when the twist angle is less than 90 degrees.