stimuli-responsive supramolecular assemblies have been widely investigated so
far [49]. Many of the CPL-active supramolecular assemblies mentioned above
exhibited concentration- and temperature-dependent CPL; the monomeric form
of the luminophore that exists in the low concentration or high temperature
shows no CPL, whereas the helical assembly formed in the high concentration or
low temperature exhibits CPL [38, 42, 45–47]. The CPL signal of compound 25
is photoresponsive, reflecting the photoisomerization of the azobenzene unit
[37]. Here, other stimuli-responsive CPL of organic luminophores is described.
Haino and coworkers reported the gelation-induced CPL of Pt(II) phenylbipyridine
complex 34 (Fig. 9.17) [50]. The complex has a similar structure to complex 29
mentioned above, but 34 possesses multiple long alkyl side-chains. 34 formed a
stacked assembly as 29 did, but the assembly formed in MCH did not display any
CD and CPL. The long alkyl side-chains provide the interassembly interaction
to afford a three-dimensional network of the one-dimensional stacked assembly. The -
three-dimensional network holds the solvent molecules in its vacancies to
form organogel. 34 formed luminescent organogel in 1-decanol at the concentration
of 9.2 Â 10
À3 mol L
À1 with decreasing temperature from 50 to 10
C. At 50
C, no
CPL signal was observed, but the CPL signals appeared at 500 nm with the gelation.
The g lum value at 10
C was 1.1 Â 10
À2
. It is noteworthy that the gelation of 34 also
triggered the AIEE; the emission intensity increased ca. 50-fold from 50 to 10
C.
Maeda and coworkers have developed pyrrole-based anion receptors, BF 2
complexes of 1,3-dipyrrolyl-1,3-propanedione [51]. The two pyrrole NH are located
at the side of the carbonyl oxygen without any anion, whereas the molecule
forms an anion complex through the N-HÁÁÁX
– interaction of the flipped pyrroles and
the C-HÁÁÁX
– interaction. The structural change of the luminophore before and after
anion-binding can be applied for the anion-responsive CPL system (Fig. 9.18). Anionresponsive CPL was observed for chiral anion-receptor 35 upon complexation with
anions such as Cl
– and tetrabutylammonium (TBA) salts [52]. 35 possesses a chiral
1,1
0 -bi-2-naphthol (BINOL) moiety as the ligand of boron. 35 displayed CPL with a
34
self-assembly
gelation
CPL
Fig. 9.17 Gelation-induced CPL of 34, a Pt(II)phenylbipyridine complex possessing
phenylisoxazoles. Adapted with permission from Wilson et al. [6]. Copyright 2018 The Royal
Society of Chemistry
214
T. Ikeda and T. Haino
far [49]. Many of the CPL-active supramolecular assemblies mentioned above
exhibited concentration- and temperature-dependent CPL; the monomeric form
of the luminophore that exists in the low concentration or high temperature
shows no CPL, whereas the helical assembly formed in the high concentration or
low temperature exhibits CPL [38, 42, 45–47]. The CPL signal of compound 25
is photoresponsive, reflecting the photoisomerization of the azobenzene unit
[37]. Here, other stimuli-responsive CPL of organic luminophores is described.
Haino and coworkers reported the gelation-induced CPL of Pt(II) phenylbipyridine
complex 34 (Fig. 9.17) [50]. The complex has a similar structure to complex 29
mentioned above, but 34 possesses multiple long alkyl side-chains. 34 formed a
stacked assembly as 29 did, but the assembly formed in MCH did not display any
CD and CPL. The long alkyl side-chains provide the interassembly interaction
to afford a three-dimensional network of the one-dimensional stacked assembly. The -
three-dimensional network holds the solvent molecules in its vacancies to
form organogel. 34 formed luminescent organogel in 1-decanol at the concentration
of 9.2 Â 10
À3 mol L
À1 with decreasing temperature from 50 to 10
C. At 50
C, no
CPL signal was observed, but the CPL signals appeared at 500 nm with the gelation.
The g lum value at 10
C was 1.1 Â 10
À2
. It is noteworthy that the gelation of 34 also
triggered the AIEE; the emission intensity increased ca. 50-fold from 50 to 10
C.
Maeda and coworkers have developed pyrrole-based anion receptors, BF 2
complexes of 1,3-dipyrrolyl-1,3-propanedione [51]. The two pyrrole NH are located
at the side of the carbonyl oxygen without any anion, whereas the molecule
forms an anion complex through the N-HÁÁÁX
– interaction of the flipped pyrroles and
the C-HÁÁÁX
– interaction. The structural change of the luminophore before and after
anion-binding can be applied for the anion-responsive CPL system (Fig. 9.18). Anionresponsive CPL was observed for chiral anion-receptor 35 upon complexation with
anions such as Cl
– and tetrabutylammonium (TBA) salts [52]. 35 possesses a chiral
1,1
0 -bi-2-naphthol (BINOL) moiety as the ligand of boron. 35 displayed CPL with a
34
self-assembly
gelation
CPL
Fig. 9.17 Gelation-induced CPL of 34, a Pt(II)phenylbipyridine complex possessing
phenylisoxazoles. Adapted with permission from Wilson et al. [6]. Copyright 2018 The Royal
Society of Chemistry
214
T. Ikeda and T. Haino