nonplanar helicene configuration according to the molecular orbital structure of the
LUMO in the original report [21]. The spin–orbit coupling is highly associated with
the degree of nonplanar configuration as discussed by Schmidt and coworkers
[40]. Thus, our synthetic strategies for [7]carbohelicene derivatives successfully
resulted in the improved Φ FL of [7]Hl-NAIQx.
In order to discuss the chiral nature in fluorescence emission, CPL spectra of [7]
carbohelicene derivatives were measured in THF (Fig. 5.3). No CPL signals were
seen in [7]Hl-Qx. In contrast with [7]Hl-Qx, (+)-(P)-[7]Hl-NAIQx (spectrum a) and
(À)-(M )-[7]Hl-NAIQx (spectrum b) successfully demonstrate CPL spectra with
negative and positive signals, respectively as shown in Fig. 5.3. The signals of
CPL are identical with those of the corresponding CD profiles in the spectral range of
longest wavelength (i.e., around 400–500 nm) [41]. The degree of CPL, i.e., the
luminescence dissymmetric factor (g lum ), is calculated by the following equation:
g lum ¼ 2(I L À I R )/(I L + I R ), where I L and I R are the luminescence intensities of left
and right circularly polarized light, respectively. By contrast with the negligible g lum
of [7]Hl-Qx, the g lum of [7]Hl-NAIQx is calculated to be 4.0 Â 10
À3 . This result is
equivalent to the g lum values observed in the monomeric form of small molecules
[25, 27, 33, 42].
To investigate the electroluminescence behaviors of [7]Hl-NAIQx, an OLED
doped with [7]Hl-NAIQx was constructed. As previously discussed [21], absorption
spectral range of [7]Hl-NAIQx extended from UV to ca. 500 nm. Fluorescence
spectrum of poly(9,9-dioctylfluorene) (PFO) range from ca. 400 to 500 nm. PFO
was therefore chosen as the host material for [7]Hl-NAIQx because of the sufficient
spectral overlap [43]. The OLED was composed of a bilayer structure with an indium
tin oxide (ITO) anode, a hole transport layer of poly(3,4-ethylene dioxythiophene):
poly-(styrenesulfonate) (PEDOT:PSS), an electron transport and emissive layer of
PFO/[7]Hl-NAIQx, and a calcium/aluminum cathode [denoted as ITO/PEDOT:
PSS/-PFO:[7]Hl-NAIQx (95:5)/Ca/Al]. Then, we obtained the J–V–L characteristics
and electroluminescence spectrum as shown in Fig. 5.4a, b. Although we observed
Fig. 5.3 CPL profiles of (a)
(+)-(P)-[7]Hl-NAIQx and
(b) (À)-(M )-[7]Hl-NAIQx
in THF (reprinted with
permission from Ref.
[21]. Copyright 2015
American Chemical
Society)
104
T. Hasobe
LUMO in the original report [21]. The spin–orbit coupling is highly associated with
the degree of nonplanar configuration as discussed by Schmidt and coworkers
[40]. Thus, our synthetic strategies for [7]carbohelicene derivatives successfully
resulted in the improved Φ FL of [7]Hl-NAIQx.
In order to discuss the chiral nature in fluorescence emission, CPL spectra of [7]
carbohelicene derivatives were measured in THF (Fig. 5.3). No CPL signals were
seen in [7]Hl-Qx. In contrast with [7]Hl-Qx, (+)-(P)-[7]Hl-NAIQx (spectrum a) and
(À)-(M )-[7]Hl-NAIQx (spectrum b) successfully demonstrate CPL spectra with
negative and positive signals, respectively as shown in Fig. 5.3. The signals of
CPL are identical with those of the corresponding CD profiles in the spectral range of
longest wavelength (i.e., around 400–500 nm) [41]. The degree of CPL, i.e., the
luminescence dissymmetric factor (g lum ), is calculated by the following equation:
g lum ¼ 2(I L À I R )/(I L + I R ), where I L and I R are the luminescence intensities of left
and right circularly polarized light, respectively. By contrast with the negligible g lum
of [7]Hl-Qx, the g lum of [7]Hl-NAIQx is calculated to be 4.0 Â 10
À3 . This result is
equivalent to the g lum values observed in the monomeric form of small molecules
[25, 27, 33, 42].
To investigate the electroluminescence behaviors of [7]Hl-NAIQx, an OLED
doped with [7]Hl-NAIQx was constructed. As previously discussed [21], absorption
spectral range of [7]Hl-NAIQx extended from UV to ca. 500 nm. Fluorescence
spectrum of poly(9,9-dioctylfluorene) (PFO) range from ca. 400 to 500 nm. PFO
was therefore chosen as the host material for [7]Hl-NAIQx because of the sufficient
spectral overlap [43]. The OLED was composed of a bilayer structure with an indium
tin oxide (ITO) anode, a hole transport layer of poly(3,4-ethylene dioxythiophene):
poly-(styrenesulfonate) (PEDOT:PSS), an electron transport and emissive layer of
PFO/[7]Hl-NAIQx, and a calcium/aluminum cathode [denoted as ITO/PEDOT:
PSS/-PFO:[7]Hl-NAIQx (95:5)/Ca/Al]. Then, we obtained the J–V–L characteristics
and electroluminescence spectrum as shown in Fig. 5.4a, b. Although we observed
Fig. 5.3 CPL profiles of (a)
(+)-(P)-[7]Hl-NAIQx and
(b) (À)-(M )-[7]Hl-NAIQx
in THF (reprinted with
permission from Ref.
[21]. Copyright 2015
American Chemical
Society)
104
T. Hasobe