Molecular orientation and dynamics of different sized organic radicals included in organic 1D nanochannels

The molecular orientation and dynamics of di-t-butylnitroxide (DTBN) and 4-oxo-2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPONE) radicals in the organic 1D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) were investigated by examining inclusion compounds (ICs) diluted by the co-inclusion of nonradicals using electron spin resonance (ESR). Spectral simulation showed that the axial rotation of DTBN or TEMPONE molecules is excited in TPP nanochannels with activation energies of 3 and 10 kJ mol(-1), respectively. The rotation axes for both DTBN and TEMPONE were determined to be almost parallel to the principal y-axis of the g tensor, which agrees with the result reported for 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) in TPP nanochannels, which has the activation energy of 5 kJ mol(-1). These results indicate that the molecular orientations of guest nitroxide radicals are almost independent of the molecular sizes of the guest radicals in TPP nanochannels, although the molecular dynamics are dependent on the molecular sizes.