initial state and the molecular conformation of the intermediates affect the
stereoselective [2 + 2] cycloaddition. Three products are possible by the cycloaddition of 2-cyclohexene-1-one in a solution as shown in Scheme 13. The reaction yield
of photocycloaddition of 2-cyclohexene-1-one in the benzene solution under UV
irradiation for 10 h (without clay) was 25%, and the ratio of the products of anti-HH,
syn-HT, and anti-HT was 8:0.1:29 (Scheme 13) [400, 401]. By adding SA, the
reaction yield remarkably increased to 72%, and the ratio of the products of anti-HH,
syn-HT, and anti-HT was 82:0.1:5 [400, 401]. It was proposed that 2-cyclohexene-1one aggregated in a parallel fashion, which led the effective photocycloaddition to
anti-HT. The photoluminescence of the excimer of 2-cyclohexene-1-one was
observed for the clay suspension.
Stilbene shows cis-trans isomerization and dimerization. Four possible
photodimers of the stilbene are obtained as shown in Scheme 14. The photochemistry of stilbazolium ion (STN
+ , Scheme 14) has been investigated to find
stereoselective photodimerization [214, 402–410]. A higher reaction yield of
photodimerization of STN
+ (the total yield, 98%, and the cis-isomer, 14%; synHT, 70%, and syn-HH, 5%, respectively) under UV irradiation for 30 min in an
aqueous suspension of a saponite than that in a solution (the total yield, 69%, and the
cis-isomer, 67%, syn-HT, 2%, and anti-HH, 2%, respectively) was reported
[402]. Cyano- and methyl-substituted STN
+ were used to show that the hetero
dimer was a major product thanks to the formation of the exciplex between the
electron-donating methyl-substituted and the electron-accepting cyano-substituted
stilbenes in the interlayer space of SA [404]. Recently, three stilbazolium derivatives, STN, MeSTN
+ , and C 16 STN
+ (in Scheme 14), were intercalated into a N-(2(2,2,3,3,4,4,4-heptafluorobutanamido)ethyl)-N,N-dimethylhexadecan-1-ammonium
bromide exchanged SA by mixing in HCl aqueous solution to examine the selectivity of the photochemical reactions [409]. Three factors, (1) electronic interactions
between the negatively charges SA surface and the stilbazolium derivatives,
(2) hydrophobic interactions among the long alkyl chains of the surfactants, and
(3) both hydrophobic and lipophobic interactions of the perfluoropropyl moieties of
the surfactant, affected the selectivity.
A [2 + 2] cycloaddition in the interlayer space of a hydrotalcite [411] led oligomer
of phenylenediacrylate with a head-to-head structure [412]. p-Phenylenediacrylate
was exchanged on a hydrotalcite (Alcamac Cl supplied by Kyowa Chemicals Ltd.)
and was irradiated a 300 W medium pressure Hg lamp for 6 h in the aqueous
suspension under stirring. The ratio of monomer, dimer, trimer, and oligomer was
0:22:31:47 after the irradiation for 6 h. In contrast, the ratio of the monomer and the
dimer in an aqueous solution of p-phenylenediacrylate (without the hydrotalcite) was
74:26, and the trimer and the oligomer were not obtained. The polymerization degree
was up to 10. The oligomer was assigned to the syn-head-to-head structure as shown
in Scheme 15. The oligomer of p-phenylenediacrylate was not obtained by the
irradiation to the powder.
The stereoselective cycloaddition was achieved by the molecular packing in the
interlayer space of clays. Aspect ratio [413] and layer charge density [414–417]
affected the yield and the selectivity. The selective cycloadditions were also reported
Photofunctions of Dye-Clay Hybrids: Recent Developments
285
stereoselective [2 + 2] cycloaddition. Three products are possible by the cycloaddition of 2-cyclohexene-1-one in a solution as shown in Scheme 13. The reaction yield
of photocycloaddition of 2-cyclohexene-1-one in the benzene solution under UV
irradiation for 10 h (without clay) was 25%, and the ratio of the products of anti-HH,
syn-HT, and anti-HT was 8:0.1:29 (Scheme 13) [400, 401]. By adding SA, the
reaction yield remarkably increased to 72%, and the ratio of the products of anti-HH,
syn-HT, and anti-HT was 82:0.1:5 [400, 401]. It was proposed that 2-cyclohexene-1one aggregated in a parallel fashion, which led the effective photocycloaddition to
anti-HT. The photoluminescence of the excimer of 2-cyclohexene-1-one was
observed for the clay suspension.
Stilbene shows cis-trans isomerization and dimerization. Four possible
photodimers of the stilbene are obtained as shown in Scheme 14. The photochemistry of stilbazolium ion (STN
+ , Scheme 14) has been investigated to find
stereoselective photodimerization [214, 402–410]. A higher reaction yield of
photodimerization of STN
+ (the total yield, 98%, and the cis-isomer, 14%; synHT, 70%, and syn-HH, 5%, respectively) under UV irradiation for 30 min in an
aqueous suspension of a saponite than that in a solution (the total yield, 69%, and the
cis-isomer, 67%, syn-HT, 2%, and anti-HH, 2%, respectively) was reported
[402]. Cyano- and methyl-substituted STN
+ were used to show that the hetero
dimer was a major product thanks to the formation of the exciplex between the
electron-donating methyl-substituted and the electron-accepting cyano-substituted
stilbenes in the interlayer space of SA [404]. Recently, three stilbazolium derivatives, STN, MeSTN
+ , and C 16 STN
+ (in Scheme 14), were intercalated into a N-(2(2,2,3,3,4,4,4-heptafluorobutanamido)ethyl)-N,N-dimethylhexadecan-1-ammonium
bromide exchanged SA by mixing in HCl aqueous solution to examine the selectivity of the photochemical reactions [409]. Three factors, (1) electronic interactions
between the negatively charges SA surface and the stilbazolium derivatives,
(2) hydrophobic interactions among the long alkyl chains of the surfactants, and
(3) both hydrophobic and lipophobic interactions of the perfluoropropyl moieties of
the surfactant, affected the selectivity.
A [2 + 2] cycloaddition in the interlayer space of a hydrotalcite [411] led oligomer
of phenylenediacrylate with a head-to-head structure [412]. p-Phenylenediacrylate
was exchanged on a hydrotalcite (Alcamac Cl supplied by Kyowa Chemicals Ltd.)
and was irradiated a 300 W medium pressure Hg lamp for 6 h in the aqueous
suspension under stirring. The ratio of monomer, dimer, trimer, and oligomer was
0:22:31:47 after the irradiation for 6 h. In contrast, the ratio of the monomer and the
dimer in an aqueous solution of p-phenylenediacrylate (without the hydrotalcite) was
74:26, and the trimer and the oligomer were not obtained. The polymerization degree
was up to 10. The oligomer was assigned to the syn-head-to-head structure as shown
in Scheme 15. The oligomer of p-phenylenediacrylate was not obtained by the
irradiation to the powder.
The stereoselective cycloaddition was achieved by the molecular packing in the
interlayer space of clays. Aspect ratio [413] and layer charge density [414–417]
affected the yield and the selectivity. The selective cycloadditions were also reported
Photofunctions of Dye-Clay Hybrids: Recent Developments
285