Local dynamics in solid matrices investigated by malachite green optical microprobes

The nonradiative rotational dynamics of phenyl rings of malachite green molecules doped in solid polymers was studied by measuring the temperature dependence of the fluorescence decay time. The rotational motion of the phenyl rings on the flat S₁ excited-state potential surface was analyzed by using the Stokes-Einstein-Debye equation. The temperature dependence of the microviscosity of the polymer hosts which controls the rotational motion of the phenyl rings was found to obey the Andrade equation with a definite activation energy which is known to be obeyed by many liquids. We found that malachite green molecules are good fluorescent probes to investigate the microscopic dynamics in solid matrices.