wavelengths (~360 nm). The use of chiral π-conjugated luminophores that
exhibit fluorescence by the πà ! π transition as CPL-active organic compounds is
desirable due to their emission in the visible region with a high emission quantum
yield. The most popular chiral π-conjugated molecule is a helicene. A helicene
is an ortho-ring-fused polycyclic aromatic compound, in which aromatic rings
are angularly annulated to give a helical structure. Helicenes have been widely
investigated from the 1950s, and the CPL of a helicene was reported by Katz and
coworkers in 2001 [12]. They synthesized [7]helicene-like compound 1 (Fig. 9.3).
The molecule exhibited polarized fluorescence at 440 nm in diluted dodecane
solution (2 Â 10
À6 mol L
À1 ), but CPL was not reported under these conditions.
However, 1 displayed CPL in the condensed dodecane solution (>1 Â 10
À3 mol L
À1 ).
The authors considered that the formation of aggregated species triggers the CPL.
S
S
O
O
O
O
C 12 H 25 O
C 12 H 25 O
C 12 H 25 O
C 12 H 25 O
N
O
O
R 1
N
O
O
R 1
R 1 = O
O
O
O
(M)-1
(1S,M)-2
(1S,M)-3
C 4 H 9
C 4 H 9
C 4 H 9
C 4 H 9
N
N
Cl
Cl
R 2
R 2
R 2 =
OMe
N
Cl
R 2
HN
R 3
R 3
R 3
R 3
Si(i-Pr) 3
R 3 =
Si
(M)-4
(M)-5
(P)-8
(M,M)-7
(M)-6
(P)-9
Fig. 9.3 CPL-active helicenes
9 Circularly Polarized Luminescence of Chirally Arranged Achiral Organic. . .
199