12 Inter-spin Interactions of Organic Radical Chains in Organic 1D. . .
429
When a sample with unpaired electrons is inserted into an external magnetic
field B 0 , the magnetic moments of electrons in the material are split into different
energy levels, depending on whether these moments are parallel or antiparallel to
B 0 . The electron magnetic moment operators are proportional to the electron spin
angular momentum values, and the proportionality constant γ (also referred to
as the gyromagnetic ratio) will be negative for electrons. Therefore, the electron
magnetic moment will be antiparallel to the angular momentum. In the external
magnetic field, the electron spin magnetic moments precess around B 0 at the
Larmor frequency ω 0 , which equals -γ B 0 . The Larmor frequencies of the various
electron magnetic moments in a specimen will differ according to the shielding
effect of neighboring electrons and/or nuclei. If an electromagnetic wave whose
frequency corresponds to the energy difference of the magnetic moments in the
field, (E = hv = ω = γ B) is applied to the sample, the electron spins in the
ground states will be excited. This phenomenon is the basis of ESR, which focusses
on electron spins. ESR studies employ a magnetic field (generated using an electric
magnet) that sweeps over the range of 0–1 T in conjunction with continuous-wave
(cw) microwave irradiation (1–100 GHz) of a sample in a cavity resonator. Pulse
ESR methods are also used for the clarification of complicated spin-lattice or interspin interactions. Variable-temperature ESR over the temperature range from 4.2 to
400 K can be applied to determine the spin concentration of each IC, as well as the
molecular orientations and dynamics of organic radicals in 1D nanochannels and
the inter-spin interactions and magnetism of 1D organic radical chains constructed
in the 1D nanochannels. In this review, the theoretical background of the analysis of
free radicals in 1D nanochannels by ESR spectroscopy is described in detail.
12.2.2 Nuclear Magnetic Resonance
When a sample without unpaired electrons is used, electron spins in the description
in the prior subsection can be replaced into nuclear magnetic moments (more
properly, only in the case of I = 1/2 (I: the nuclear spin quantum number of
the nuclei). If I > 1/2, see Sect. 12.2.3.1 and references [57–59]). However, the
proportionality constant γ will be positive for most nuclei. Therefore, the nuclear
magnetic moment will typically be parallel to the angular momentum. In modernday NMR analyses, radio-frequency pulses (ω; in the range of 10 2 –10 3 MHz) are
applied to a sample surrounded by a coil and subjected to an external magnetic field
of approximately 1–15 T in conjunction with a superconducting magnet. In the case
of metals or metal nanoparticles, analyses are conducted in a static external magnetic
field using a cw radio-frequency source with either a permanent or electric magnet
[60, 61]. Room temperature solution 1 H NMR spectroscopy is primarily performed
for the structural elucidation of host materials such as TPP and CLPOT.
429
When a sample with unpaired electrons is inserted into an external magnetic
field B 0 , the magnetic moments of electrons in the material are split into different
energy levels, depending on whether these moments are parallel or antiparallel to
B 0 . The electron magnetic moment operators are proportional to the electron spin
angular momentum values, and the proportionality constant γ (also referred to
as the gyromagnetic ratio) will be negative for electrons. Therefore, the electron
magnetic moment will be antiparallel to the angular momentum. In the external
magnetic field, the electron spin magnetic moments precess around B 0 at the
Larmor frequency ω 0 , which equals -γ B 0 . The Larmor frequencies of the various
electron magnetic moments in a specimen will differ according to the shielding
effect of neighboring electrons and/or nuclei. If an electromagnetic wave whose
frequency corresponds to the energy difference of the magnetic moments in the
field, (E = hv = ω = γ B) is applied to the sample, the electron spins in the
ground states will be excited. This phenomenon is the basis of ESR, which focusses
on electron spins. ESR studies employ a magnetic field (generated using an electric
magnet) that sweeps over the range of 0–1 T in conjunction with continuous-wave
(cw) microwave irradiation (1–100 GHz) of a sample in a cavity resonator. Pulse
ESR methods are also used for the clarification of complicated spin-lattice or interspin interactions. Variable-temperature ESR over the temperature range from 4.2 to
400 K can be applied to determine the spin concentration of each IC, as well as the
molecular orientations and dynamics of organic radicals in 1D nanochannels and
the inter-spin interactions and magnetism of 1D organic radical chains constructed
in the 1D nanochannels. In this review, the theoretical background of the analysis of
free radicals in 1D nanochannels by ESR spectroscopy is described in detail.
12.2.2 Nuclear Magnetic Resonance
When a sample without unpaired electrons is used, electron spins in the description
in the prior subsection can be replaced into nuclear magnetic moments (more
properly, only in the case of I = 1/2 (I: the nuclear spin quantum number of
the nuclei). If I > 1/2, see Sect. 12.2.3.1 and references [57–59]). However, the
proportionality constant γ will be positive for most nuclei. Therefore, the nuclear
magnetic moment will typically be parallel to the angular momentum. In modernday NMR analyses, radio-frequency pulses (ω; in the range of 10 2 –10 3 MHz) are
applied to a sample surrounded by a coil and subjected to an external magnetic field
of approximately 1–15 T in conjunction with a superconducting magnet. In the case
of metals or metal nanoparticles, analyses are conducted in a static external magnetic
field using a cw radio-frequency source with either a permanent or electric magnet
[60, 61]. Room temperature solution 1 H NMR spectroscopy is primarily performed
for the structural elucidation of host materials such as TPP and CLPOT.