Correlation Between Orientation of the Stacked π‐Electron Systems and Chiroptical Properties

Abstract

The correlation between the orientation of the two π-electron systems and the chiroptical properties was investigated using two types of optically active X-shaped molecules consisting of planar chiral [2.2]paracyclophanes. The X-shaped molecules exhibited high photoluminescence quantum efficiencies and good circularly polarized luminescence properties with relatively high anisotropy factors of the order of 10 À 3 . It was experimentally and theoretically elucidated that the chiroptical properties of the two molecules were almost identical, regardless of the orientation of the stacked π-electron systems.

Aggregation-induced emission from optically active X-shaped molecules based on planar chiral [2.2]paracyclophane

“…4 A, the mirror image CD spectra were observed for both the enantiomers of aggregates 11 , with the first Cotton effects of the ( S p )- and ( R p )-isomers being positive and negative, respectively. These signs are identical to those of a series of optically active X-shaped molecules reported previously 32 , 36 , 37 , 46 . However, their noisy CPL signals were barely detected (Fig.…”

“…Weak emission was detected around 445 nm, as shown in the inset of Fig. 2 B, which can be observed in a series of X-shaped molecules 32 , 37 , 46 , 47 . These PL signals were not affected by the polarity change arose from the formation of aggregates; therefore, they were assigned to the general PL peaks of the X-shaped skeleton 32 , 37 , 46 , 47 .…”

“…2 B, which can be observed in a series of X-shaped molecules 32 , 37 , 46 , 47 . These PL signals were not affected by the polarity change arose from the formation of aggregates; therefore, they were assigned to the general PL peaks of the X-shaped skeleton 32 , 37 , 46 , 47 . On the other hand, a clear blue-shift was observed for the strong emission peaks; for example, emission peak top in the THF/H 2 O (10/90) solution appeared at 609 nm, and that appeared at 771 nm in the THF/H 2 O (90/10) solution.…”

“…The molecular orbitals of the model compound, in which the dodecyloxy groups of ( S p )- 11 were replaced with methoxy groups, in the ground state were calculated using density functional theory (DFT) and compared with those of the X-shaped molecule prepared recently 46 , as shown in Fig. 5 .…”

“…Figure 6 A shows the LUMOs and HOMOs in the S 1 states of the ( S p )- 11 model, and Fig. 6 B shows those of the corresponding X-shaped molecule 46 . Their orbitals were similar; the LUMOs were delocalized throughout the molecules, and the HOMOs were localized on one of the two π-electron systems.…”