Parallel Relaxation Pathways of Malachite Green Revealed by Ultrafast Pump-Dump-Probe Spectroscopy

【Introduction】 Malachite green (MG) is one of triphenylmethane dyes that are well-known to undergo ultrafast relaxation upon photoexcitation. The relaxation dynamics of this prototypical molecule has been intensively studied by a variety of spectroscopic methods, and it was found that the relaxation dynamics can be characterized by three typical time constants of τ1=150 fs, τ2=0.6 ps and τ3=3 ps (solvent dependent). As shown by a simple relaxation scheme in Figure 1, it is generally believed that the relaxation is accompanied by cooperative rotational motions of the phenyl groups, which leads to a ground-state intermediate (Sx state). However, owing to spectral overlaps of these relevant states, the relaxation scheme of MG is still in dispute. To clarify its relaxation pathways, we studied the ultrafast relaxation dynamics using pump-dump-probe spectroscopy.