Thermodynamic and Dynamic Transitions and Interaction Aspects in Reorientation Dynamics of Molecular Probe in Organic Compounds : A Series of 1-alkanols with TEMPO .

The spectral and dynamic properties of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in a series of 1-alkanols ranging from methanol to 1-decanol over a temperature range 100-300 K were investigated by electron spin resonance (ESR ). The main characteristic ESR temperatures connected with slow to fast motion regime transition; T 50G 's and T X1 fast 's are situated above the corresponding glass temperatures, T g , and for the shorter members, the T 50G 's lie above or close to melting point, T m , while the longer ones the T 50G < T m relationship indicates that the TEMPO molecules are in the local disordered regions of the crystalline media . The T 50G 's and especially T X1 fast 's are compared with the dynamic crossover temperatures, T X VISC = 8.72 M 0.66 , as obtained by fitting the viscosity data in the liquid n-alkanols with the empirical power law. In particular, for N C > 6, the T X1 fast 's lie rather close to the T X VISC resembling apolar n-alkanes [PCCP 2018, 20 ,11145-11151], while for N C < 6, they are situated in the vicinity of T m . The absence of a coincidence for lower 1-alkanols indicates that the T 50G is significantly influenced by the mutual interaction between the polar TEMPO and the protic polar medium due to the increased polarity and proticity destroyed by the larger-scale melting transition.