Similarly, the cis isomer 46a could also encapsulate one acetone molecule in its
cavity with multiple non-covalent interactions, including CÀHÁÁÁO hydrogen bonding and two pairs of CÀHÁÁÁπ interactions (Fig. 10b). The similar molecular recognition property has not been observed in the reported N(H)-bridged azacalixarenes.
Moreover, it was found that two molecules of 46a can form a dimer through the
O
δÀ
ÁÁÁN
δ+ and O
δÀ
ÁÁÁC
δ+ interactions with two acetone molecules and two
dichloromethane molecules in its cavity (Fig. 10c).
Fullerenes and their derivatives have drawn much attention for their wide potential
applications. Design and synthesis of new classes of supramolecular containers for
fullerenes are of great interest in relation to the development of fullerene-based
functional materials. Calix[2]triptycene[2]arenes have enough large and well-defined
electron-rich cavity for fullerenes [23]. Consequently, 4b and 5b could form 1:1 stable
complexes with C 60 and C 70 with the association constants (K a ) more than
1 Â 10
4 M
À1 by the fluorescence titrations, which were significantly higher than
those ones (9–1300 M
À1
) of 1:1 complexes between C 60 and the classical calixarene
derivatives [32]. This probably revealed the introduction of the triptycene moiety not
only fixed conformations of the macrocycles but also enhanced the interaction of
concave cavities of the macrocycles with the electron-deficient convex surface of the
fullerenes. Oxacalixarene 35d with extended cavity could also form 1:1 complexes
with C 60 and C 70 , and K a values for 35d•C 60 and 35d•C 70 were (7.54 Æ 0.29) Â 10
4
and (8.96 Æ 0.31) Â 10
4 M
À1
, respectively [25]. Similarly, homooxacalixarene
analogues 39a–d and 40a–d with fixed conformations and large electron-rich cavities
showed efficient complexation abilities toward fullerenes C 60 and C 70 as well [28], and
K a values for the 1:1 complexes were over 10
4 M
À1
.
Macrocycle 13 with electron-rich cavities could form 1:1 complexes with paraquat derivatives 53a–d (Fig. 11), and the association constants (K a ) are all over
10
2 M
À1 [20]. It was found that they could show strong complexation capabilities
with a series of paraquat derivatives. Oxacalixarenes 35d and 36d with large enough
cavities and fixed conformations could also form 1:1 complexes with paraquat
derivatives, and the K a values were about 10
3 M
À1 for 35d and 10
2 M
À1 for 36d
[26]. Similarly, 38a showed moderate complexation abilities toward various
bipyridinium salts, but affinities of 38b toward the guests were found to be substantially stronger, which might be due to the additional non-covalent interactions
between the aniline group and the guests [27]. Formation of the complexes was
further evidenced by crystal structures of 35d•53a, 35d•53f, and 38b•53i (Fig. 12).
Interestingly, complexation and dissociation of the complex based on 35d containing
1,8-naphthridine subunits could be easily controlled by acid/base stimuli or by the
addition and removal of Hg
2+ ions [26]. It was further found 35d showed a highly
selective fluorescence sensing toward Hg
2+ [33]. Moreover, 35d could encapsulate
π-extended viologens 54–55 to form pseudo[3]rotaxane-type complexes in solution
and solid state, and the complexation between the host and the guests could be
reversibly switched by acid and base. Nonsymmetric structure of 35d also resulted in
orientationally selective pseudorotaxanes depending to different lengths of the
linkers in the guests, which might be ascribed to different complexation modes
between the components in the complexes [34].
6 Triptycene-Derived Macrocyclic Arenes
159
cavity with multiple non-covalent interactions, including CÀHÁÁÁO hydrogen bonding and two pairs of CÀHÁÁÁπ interactions (Fig. 10b). The similar molecular recognition property has not been observed in the reported N(H)-bridged azacalixarenes.
Moreover, it was found that two molecules of 46a can form a dimer through the
O
δÀ
ÁÁÁN
δ+ and O
δÀ
ÁÁÁC
δ+ interactions with two acetone molecules and two
dichloromethane molecules in its cavity (Fig. 10c).
Fullerenes and their derivatives have drawn much attention for their wide potential
applications. Design and synthesis of new classes of supramolecular containers for
fullerenes are of great interest in relation to the development of fullerene-based
functional materials. Calix[2]triptycene[2]arenes have enough large and well-defined
electron-rich cavity for fullerenes [23]. Consequently, 4b and 5b could form 1:1 stable
complexes with C 60 and C 70 with the association constants (K a ) more than
1 Â 10
4 M
À1 by the fluorescence titrations, which were significantly higher than
those ones (9–1300 M
À1
) of 1:1 complexes between C 60 and the classical calixarene
derivatives [32]. This probably revealed the introduction of the triptycene moiety not
only fixed conformations of the macrocycles but also enhanced the interaction of
concave cavities of the macrocycles with the electron-deficient convex surface of the
fullerenes. Oxacalixarene 35d with extended cavity could also form 1:1 complexes
with C 60 and C 70 , and K a values for 35d•C 60 and 35d•C 70 were (7.54 Æ 0.29) Â 10
4
and (8.96 Æ 0.31) Â 10
4 M
À1
, respectively [25]. Similarly, homooxacalixarene
analogues 39a–d and 40a–d with fixed conformations and large electron-rich cavities
showed efficient complexation abilities toward fullerenes C 60 and C 70 as well [28], and
K a values for the 1:1 complexes were over 10
4 M
À1
.
Macrocycle 13 with electron-rich cavities could form 1:1 complexes with paraquat derivatives 53a–d (Fig. 11), and the association constants (K a ) are all over
10
2 M
À1 [20]. It was found that they could show strong complexation capabilities
with a series of paraquat derivatives. Oxacalixarenes 35d and 36d with large enough
cavities and fixed conformations could also form 1:1 complexes with paraquat
derivatives, and the K a values were about 10
3 M
À1 for 35d and 10
2 M
À1 for 36d
[26]. Similarly, 38a showed moderate complexation abilities toward various
bipyridinium salts, but affinities of 38b toward the guests were found to be substantially stronger, which might be due to the additional non-covalent interactions
between the aniline group and the guests [27]. Formation of the complexes was
further evidenced by crystal structures of 35d•53a, 35d•53f, and 38b•53i (Fig. 12).
Interestingly, complexation and dissociation of the complex based on 35d containing
1,8-naphthridine subunits could be easily controlled by acid/base stimuli or by the
addition and removal of Hg
2+ ions [26]. It was further found 35d showed a highly
selective fluorescence sensing toward Hg
2+ [33]. Moreover, 35d could encapsulate
π-extended viologens 54–55 to form pseudo[3]rotaxane-type complexes in solution
and solid state, and the complexation between the host and the guests could be
reversibly switched by acid and base. Nonsymmetric structure of 35d also resulted in
orientationally selective pseudorotaxanes depending to different lengths of the
linkers in the guests, which might be ascribed to different complexation modes
between the components in the complexes [34].
6 Triptycene-Derived Macrocyclic Arenes
159