Temperature-dependent reorientation dynamics of laser dyes in alkane and alcohol solvents

The rotational dynamics of similar sized coumarin 6 (C6), coumarin 7 (C7), and coumarin 30 (C30) laser dyes has been studied in alkane and alcohol solvents using steady-state and time-resolved fluorescence depolarization methods. The estimated rotational reorientation times of these probes are observed to vary linearly as a function of viscosity over the range of temperatures studied. It is found that the rotational reorientation time measurements of these molecules in alcohol and alkane typically have relaxation times on the order of picoseconds. The rotational reorientation times of the C7 molecule are greater than those of the C6 and C30 molecules. It was observed that C7 rotates faster in both the solvents than C6 and C30, indicating that the effects of the medium and structural differences of molecules lead to slower rotation. (author)