10 Circularly Polarized Luminescence (CPL) Based on Planar …
345
and Oosterhoff 1967); a representative example is shown in Fig. 10.1. Because of
the forbidden n-π* transition, the molecule emitted CPL with a very large g lum value
of +3.5 × 10
−2 . This value was long considered the champion value for a long time
in the small organic molecules in a diluted solution, although the Φ PL was quite
low (Φ PL = 1 × 10
−5 ). Various CPL emitters with the central chirality have been
reported to show large g lum values. As the representative examples, naphthyl (Amako
et al. 2014) and naphthalimide (Sheng et al. 2016) emissive units were connected
on chiral cyclic scaffolds, which showed CPL emission from the intramolecular
aggregate (excimer) of the aromatic units with |g lum | values of 9.4 × 10
−3 (Φ PL =
0.02) and 1.4 × 10
−2 , respectively. In 2017, the champion g lum value was updated
for the cylindrical molecule 4 with cylinder helicity (Fig. 10.2), and it was on the
order of 10
−1 (|g lum | = 1.5 × 10
−1 and Φ PL = 0.80) (Sato et al. 2017). Theoretical
studies revealed a large m, as well as linearly oriented m and μ (θ = 180°).
Fig. 10.1 Representative examples of CPL emitters with central chirality
Fig. 10.2 Cylindrical
molecules with an excellent
CPL profile