Inter-Spin Interaction of CLPOT Inclusion Compounds with 1D Molecular Chains of 4-X-TEMPO Radicals in the Temperature Range of 4.2–300 K

Abstract

ESR measurements of [CLPOT-(4-X-TEMPO)] inclusion compounds (CLPOT = 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine, and 4-X-TEMPO = 4-substituted-2,2,6,6-tetramethyl-1-piperidinyloxyl radical) with 1D organic-radical molecular chains constructed in organic 1D nanochannels used as templates were conducted in the range of temperatures from 4.2 to 300 K. The peak-to-peak line width (ΔBpp) of all isotropic ESR spectra of the [CLPOT-(4-X-TEMPO)] was much narrower in the whole temperature range than the estimation based on the Van Vleck’s formula for the second moment of the rigid lattice model. In addition, the line profiles of all ESR spectra of the [CLPOT-(4-X-TEMPO)] became Lorentzian in the whole temperature range, compared with our previous results using tris(o-phenylenedioxy)cyclotriphosphazene (TPP) as templates in which the ESR profiles were temperature-dependent. These results indicate that the narrower ESR line width of the [CLPOT-(4-X-TEMPO)] may be caused not by motional narrowing but by 3D exchange interaction even at room temperature although the magnitude was less than 1 K.

Electron Spin Resonance Study of Molecular Orientation and Dynamics of Phenyl Imino and Nitronyl Nitroxide Radicals in Organic 1D Nanochannels of Tris(o-phenylenedioxy)cyclotriphosphazene

“…This suggests the possibility of developing [(organic 1D porous material)–(organic radical)] inclusion compounds (O1DP-ORICs) for probing the magnetic exchange between radicals by the appropriate choice of host and guest materials for the control of molecular orientation and dynamics of the guest radicals in the nanochannels. In fact, such ICs were reported, in which the 3D exchange interaction was observed by the use of a porous material with larger pore diameter than TPP . The inclusion of several organic radicals in TPP nanochannels and the molecular orientation and dynamics of guest molecules have been confirmed using ESR spectroscopy − and spectral reproduction by means of computer simulation. − In addition, the molecular orientation and dynamics of organic radicals in confined nanospace such as not only in 1D nanochannels but also in 0D cavities in cyclodextrins or in micelles has been reported …”

“…In fact, such ICs were reported, in which the 3D exchange interaction was observed by the use of a porous material with larger pore diameter than TPP. 24 The inclusion of several organic radicals in TPP nanochannels and the molecular orientation and dynamics of guest molecules have been confirmed using ESR spectroscopy 25−29 and spectral reproduction by means of computer simulation. 30−32 In addition, the molecular orientation and dynamics of organic radicals in confined nanospace such as not only in 1D nanochannels but also in 0D cavities in cyclodextrins 33 or in micelles has been reported.…”