Preparation and Characterization of Inclusion Compounds Using TEMPOL and an Organic 1-D Nanochannel as a Template

Abstract

Inclusion of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPOL) radical into an organic one-dimensional (1-D) nanochannels formed in guest-free tris (o-phenylenedioxy)cyclotriphosphazene (TPP) was attempted. The inclusion of TEMPOL molecules adsorbed into the TPP nanochannel and their molecular orientation and dynamics were confirmed by temperature-dependent election spin resonance (ESR) measurements. In the specimens prepared by co-precipitation, the existence of 1-D spin diffusion was suggested from the ESR line shape, but the diffusion was not as effective as in the case of the TPP and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) inclusion compound reported in our previous article. These results imply a new methodology for the preparation of a new organic magnet using TPP as a template.

ESR study of the molecular orientation and dynamics of stable organic radicals included in the 1‐D organic nanochannels of 2,4,6‐tris‐4‐(chlorophenoxy)‐1,3,5‐triazine

“…The correlation time τ R of the rotational motion was estimated to be 10 −9 s < τ R < 10 −6 s . Such behaviors were observed also in TPP/(organic radical) ICs with the guest radicals other than TEMPO …”

“…TPP nanochannels have periodic bottleneck structures, and the minimum diameter part (bottleneck) of guest‐free TPP is 0.46 nm . The diameter of the TPP nanochannels extends according to guest inclusion; however, the bottleneck is estimated to be at most 0.63 nm, even when the largest guest molecules, such as TEMPOL or mesitylene, are included . It is difficult to determine the molecular orientation of a guest in the TPP nanochannels by X‐ray crystal analysis.…”

“…0.9 nm in both cases). On the other hand, the bottleneck of CLPOT nanochannels (1.4 nm) is sufficiently large with respect to the molecular size of TEMPO or TEMPOL, whereas the length along the channel axis ( ca . 0.7 nm) is comparable.…”

Preparation and Characterization of New Inclusion Compounds Using Stable Nitroxide Radicals and an Organic 1-D Nanochannel as a Template

“…The principal values of g and A tensors are given in reference 32. The line shape of the isolated TEMPOL component was averaged with increasing temperature, and a correlation time of rotational motion, τ R , was estimated to be 9 × 10 -8 s at 285 K. This is comparable to τ R = 5 × 10 -7 s at 293 K of the IC using TPP and TEMPOL prepared by the adsorption method [32]. This implies that co-inclusion of mesitylene hardly contributes to molecular motion of TEMPOL in the TPP nanochannels.…”

Molecular Orientation and Dynamics of Different Sized Organic Radicals Included in Organic 1D Nanochannels

“…10,23 However, such an ESR signal for 4 may be negligible because the ESR signal of TEMPO derived from TEMP is expected to be weaker than that of the target radical (e.g., TEMPONE in this case) by a few orders of magnitude. 10,23 The 17 Coincidentally, the pore diameter is comparable to the molecular cross-section of TEMPONE, and it is slightly large to accommodate TEMPO (see Table 1). Therefore, the difference in the dynamics of TEMPO and TEMPONE included in TPP nanochannels and that in the intermolecular interaction between radical and spacer molecules are probably significant (see section 3.3).…”