examined to find C 2 AZC 2 N
+ -clay (with CEC of 108 and 84 meq/100 g) increased by
the UV irradiation, while that with 71 meq/100 g did not change. Changes of the
basal spacings of KF, TSM, and SA intercalated AZC 2 N
+
C 2 OH in the presence of
phenol by the UV irradiation are summarized in Table 4 [167]. The fraction of the
cis-isomer of AZC 2 N
+ C 2 OH in TSM was estimated to be ca. 50%, and it was larger
than that in KF (ca. 30%).
To enhance the structural change by the photoinduced adsorption, the following
parameters were proposed: (1) fraction of cis-isomer at the photostationary state
[167, 344], (2) amount [344], and (3) orientation [167] of azobenzene derivative
(corresponding to the surface coverage).
The photoinduced adsorption of photochromic compounds was also reported
recently [374, 382, 450, 451]. As discussed in Sect. 5.1.3, photochromism of
spiropyran was affected by the presence of nanospace materials including
mesoporous silicas and smectites. Color of 6-NO 2 -MC (Scheme 12) photochemically formed from 6-NO 2 -SP was blue in toluene under UV irradiation, while the
color of it was red in the presence of HE [374]. Red-colored sediment was collected
by storing the suspension in the dark so that the adsorbed amount of MC onto HE
was followed, showing that the 6-NO 2 -SP was adsorbed on HE with the first-order
kinetics [374]. The adsorbed amount of 6-NO 2 -MC was 2.8 mg/100 g. The photoinduced adsorption is thought as molecular migration between hydrophobic and
hydrophilic phases by using the bistability of the photochromic compound.
Mesoporous silicas were used as adsorbent of photo 6-NO 2 -MC, which is named
as “photoinduced adsorption” [382, 450, 452]. Photoinduced migration of SA/MC
between the mesoporous silicas and the organophilic clay [381, 382] was reported to
lead the reversibility of the negative photochromisms. The organically modified clay
was thought to host less polar 6-NO 2 -SP, which formed by the negative photochromisms of 6-NO 2 -MC accommodated in the mesoporous silica. The thermal coloration of 6-NO 2 -SP to 6-NO 2 -MC accelerated by using the mesoporous silicas with
larger pore size [382] and that whose external surface was functionalized with
phenyl groups [451], suggesting that the diffusion inside the pore is important and
the intraparticle diffusion was more efficient than the interparticle diffusion.
6 Conclusions and Future Perspectives
Recent developments on the preparation and the photofunctions of dye-clay hybrids
are reviewed. Photofunctions have been systematically controlled and discussed
based on the variation of hosts, guests, and their compositions. These developments
led to further understanding of the structure and composition-property relationships,
which may provide advance knowledge to optimize materials’ performances. Not
only the nanostructure design by using host-guest interfaces has been revised, but the
search for raw materials and their synthesis of new host materials have been also
done. Successful morphosyntheses of known materials to obtain well-defined particles and single crystals with narrow particle size distribution expanded the
294
T. Yamaguchi et al.
+ -clay (with CEC of 108 and 84 meq/100 g) increased by
the UV irradiation, while that with 71 meq/100 g did not change. Changes of the
basal spacings of KF, TSM, and SA intercalated AZC 2 N
+
C 2 OH in the presence of
phenol by the UV irradiation are summarized in Table 4 [167]. The fraction of the
cis-isomer of AZC 2 N
+ C 2 OH in TSM was estimated to be ca. 50%, and it was larger
than that in KF (ca. 30%).
To enhance the structural change by the photoinduced adsorption, the following
parameters were proposed: (1) fraction of cis-isomer at the photostationary state
[167, 344], (2) amount [344], and (3) orientation [167] of azobenzene derivative
(corresponding to the surface coverage).
The photoinduced adsorption of photochromic compounds was also reported
recently [374, 382, 450, 451]. As discussed in Sect. 5.1.3, photochromism of
spiropyran was affected by the presence of nanospace materials including
mesoporous silicas and smectites. Color of 6-NO 2 -MC (Scheme 12) photochemically formed from 6-NO 2 -SP was blue in toluene under UV irradiation, while the
color of it was red in the presence of HE [374]. Red-colored sediment was collected
by storing the suspension in the dark so that the adsorbed amount of MC onto HE
was followed, showing that the 6-NO 2 -SP was adsorbed on HE with the first-order
kinetics [374]. The adsorbed amount of 6-NO 2 -MC was 2.8 mg/100 g. The photoinduced adsorption is thought as molecular migration between hydrophobic and
hydrophilic phases by using the bistability of the photochromic compound.
Mesoporous silicas were used as adsorbent of photo 6-NO 2 -MC, which is named
as “photoinduced adsorption” [382, 450, 452]. Photoinduced migration of SA/MC
between the mesoporous silicas and the organophilic clay [381, 382] was reported to
lead the reversibility of the negative photochromisms. The organically modified clay
was thought to host less polar 6-NO 2 -SP, which formed by the negative photochromisms of 6-NO 2 -MC accommodated in the mesoporous silica. The thermal coloration of 6-NO 2 -SP to 6-NO 2 -MC accelerated by using the mesoporous silicas with
larger pore size [382] and that whose external surface was functionalized with
phenyl groups [451], suggesting that the diffusion inside the pore is important and
the intraparticle diffusion was more efficient than the interparticle diffusion.
6 Conclusions and Future Perspectives
Recent developments on the preparation and the photofunctions of dye-clay hybrids
are reviewed. Photofunctions have been systematically controlled and discussed
based on the variation of hosts, guests, and their compositions. These developments
led to further understanding of the structure and composition-property relationships,
which may provide advance knowledge to optimize materials’ performances. Not
only the nanostructure design by using host-guest interfaces has been revised, but the
search for raw materials and their synthesis of new host materials have been also
done. Successful morphosyntheses of known materials to obtain well-defined particles and single crystals with narrow particle size distribution expanded the
294
T. Yamaguchi et al.