452
H. Kobayashi
the E a values for PhIN and PhNN rotations in TPP nanochannel (19 and 45 kJ
mol −1 ) are much greater than those for such nitroxide radicals [44]. These results
indicate that the τ R values in TPP nanochannels are determined by the moment
of inertia for guest radicals. Alternatively, these data may result from the strong
interactions of PhIN or PhNN with the surrounding host walls formed by the phenyl
rings of TPP molecules. Interactions may also occur with neighboring spacers
in the TPP nanochannels as a result of the delocalization of the spin density
on the iminonitroxide groups of PhIN radicals or the nitronylnitroxide group of
NN radicals, in contrast to the behavior of TEMPO (in which the spin density
is wrapped inside). However, the E a value for PhIN rotation is smaller than that
for 4-hydroxy-TEMPO (TEMPOL) in TPP nanochannels (26 kJ mol −1 ) [43]. The
E a for TEMPOL rotation has been reported to be much larger than those for
other TEMPO derivatives due to the different molecular orientation of TEMPOL
in TPP nanochannels, as shown above (see Fig. 12.9). In the case of PhIN and
TEMPOL in TPP nanochannels, the NO groups are approximately perpendicular to
the nanochannel axis and also close to the nanochannels walls formed by the phenyl
rings of TPP molecules [14, 28, 29], assuming that the rotational axis is parallel to
the channel axis. The larger E a for TEMPOL rotation in TPP nanochannel may be
caused by the additional interaction between the OH groups (rather than the NO
groups) of TEMPOL and the π -clouds on the phenyl rings of the TPP wall. This is
as opposed to hydrogen bridging of the OH groups of TEMPOL with the oxygen
atoms or the lone pairs of the nitrogen atoms of the TPP structure.
The molecular orientations of NN radicals in TPP or CLPOT nanochannels is as
same each other as discussed in Sects. 12.4 and 12.5, that is, the molecular long axis
is parallel to the channel axis. In addition, the E a value for PhNN rotation in TPP
nanochannel is larger than that for PhNN rotation in CLPOT nanochannel (37 kJ
mol −1 , see Fig. 12.7). This result may be due to the smaller pore diameter of TPP
nanochannels compared to those in CLPOT. The E a value for PhNN rotation in
TPP nanochannel is smaller than that for p-NPNN in CLPOT nanochannels (54 kJ
mol −1 , see Fig. 12.7). This outcome is attributed to the smaller moment of inertia
for PhNN compared to that for p-NPNN. In addition, PhNN rotation gives larger
E a value than PhIN rotation. It may be attributable to the difference in the steric
hindrances of NN and IN groups, or to the stronger intermolecular interactions of
PhNN with neighboring spacer molecules.
12.6 1D 4-X-TEMPO Chains Constructed in CLPOT
and TPP Nanochannels
The ESR measurements for organic radicals in 1D nanochannels dispersed by
spacer molecules were conducted in Sects. 12.4 and 12.5. In such systems, dipolar
and/or exchange interaction between radicals can be ignored due to the longer
intermolecular distance, although 1D molecular chains are formed (see Fig. 12.12a).
H. Kobayashi
the E a values for PhIN and PhNN rotations in TPP nanochannel (19 and 45 kJ
mol −1 ) are much greater than those for such nitroxide radicals [44]. These results
indicate that the τ R values in TPP nanochannels are determined by the moment
of inertia for guest radicals. Alternatively, these data may result from the strong
interactions of PhIN or PhNN with the surrounding host walls formed by the phenyl
rings of TPP molecules. Interactions may also occur with neighboring spacers
in the TPP nanochannels as a result of the delocalization of the spin density
on the iminonitroxide groups of PhIN radicals or the nitronylnitroxide group of
NN radicals, in contrast to the behavior of TEMPO (in which the spin density
is wrapped inside). However, the E a value for PhIN rotation is smaller than that
for 4-hydroxy-TEMPO (TEMPOL) in TPP nanochannels (26 kJ mol −1 ) [43]. The
E a for TEMPOL rotation has been reported to be much larger than those for
other TEMPO derivatives due to the different molecular orientation of TEMPOL
in TPP nanochannels, as shown above (see Fig. 12.9). In the case of PhIN and
TEMPOL in TPP nanochannels, the NO groups are approximately perpendicular to
the nanochannel axis and also close to the nanochannels walls formed by the phenyl
rings of TPP molecules [14, 28, 29], assuming that the rotational axis is parallel to
the channel axis. The larger E a for TEMPOL rotation in TPP nanochannel may be
caused by the additional interaction between the OH groups (rather than the NO
groups) of TEMPOL and the π -clouds on the phenyl rings of the TPP wall. This is
as opposed to hydrogen bridging of the OH groups of TEMPOL with the oxygen
atoms or the lone pairs of the nitrogen atoms of the TPP structure.
The molecular orientations of NN radicals in TPP or CLPOT nanochannels is as
same each other as discussed in Sects. 12.4 and 12.5, that is, the molecular long axis
is parallel to the channel axis. In addition, the E a value for PhNN rotation in TPP
nanochannel is larger than that for PhNN rotation in CLPOT nanochannel (37 kJ
mol −1 , see Fig. 12.7). This result may be due to the smaller pore diameter of TPP
nanochannels compared to those in CLPOT. The E a value for PhNN rotation in
TPP nanochannel is smaller than that for p-NPNN in CLPOT nanochannels (54 kJ
mol −1 , see Fig. 12.7). This outcome is attributed to the smaller moment of inertia
for PhNN compared to that for p-NPNN. In addition, PhNN rotation gives larger
E a value than PhIN rotation. It may be attributable to the difference in the steric
hindrances of NN and IN groups, or to the stronger intermolecular interactions of
PhNN with neighboring spacer molecules.
12.6 1D 4-X-TEMPO Chains Constructed in CLPOT
and TPP Nanochannels
The ESR measurements for organic radicals in 1D nanochannels dispersed by
spacer molecules were conducted in Sects. 12.4 and 12.5. In such systems, dipolar
and/or exchange interaction between radicals can be ignored due to the longer
intermolecular distance, although 1D molecular chains are formed (see Fig. 12.12a).