Inter-Spin Interactions of 1D Chains of Different-Sized Nitroxide Radicals Incorporated in the Organic 1D Nanochannels of Tris(o-phenylenedioxy)cyclotriphosphazene

Variable-temperature electron spin resonance (ESR) was measured for one-dimensional (1D) molecular chains formed using different-sized organic radicals incorporated into the 1D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP). The ESR spectra for the molecular chains of 4-oxo-2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPONE) incorporated in the TPP nanochannels ([TPP-TEMPONE]) exhibited anisotropic three-dimensional (3D) spin diffusion at temperatures close to room temperature. In contrast, 1D spin diffusion was observed even at low temperatures indicating a longer rotational diffusion correlation time or the termination of molecular motion of the guest radicals dispersed in the TPP nanochannels. The temperature range for 1D spin diffusion in [TPP-TEMPONE] was higher and wider than that of TPP inclusion compounds incorporating smaller nitroxide radicals, such as di-t-butyl nitroxide (DTBN), or 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) radicals, as previously reported. Thus, inter-spin interactions of the organic-radical 1D molecular chains formed in size-adjustable nanochannels, such as TPP, are influenced by the molecular size and dynamics of guest radicals, and temperature.