Direct evidence for the glass-crystalline transformation in solid ethanol by means of a nitroxide spin probe

The phase transition phenomenon in solid ethanol doped with nitroxyl radicals was studied by continuous and pulsed electron paramagnetic resonance (EPR) spectroscopy. The appearance of the crystalline state from the ethanol glass was for the first time directly monitored in the course of an EPR experiment. The switching of dynamical constraints in the nitroxide local environment was thermally controlled within the same host matrix. The achieved distinct molecular order was further characterized by measuring the effective spin lattice relaxation time (T1) of the entrapped nitroxides from 80 to 20 K and simulating data assuming a two-phonon Raman process.