Nonlinear conversion dynamics from self-trapped exciton states to a macroscopic photoinduced phase in strongly correlated organic radical crystals

Nonlinear conversion from self-trapped exciton (STE) states with local lattice distortions to a macroscopic photoinduced phase has been investigated in strongly correlated organic radical 1,3,5-trithia-2,4,6-triazapentalenyl crystals through luminescence and Raman-scattering measurements. The two-photon luminescence from STEs in the diamagnetic phase shows a quenching and a redshift with a clear threshold excitation photon density. The redshift directly represents a change in the local potential surface for the excited states, which stabilizes the excited domain and subsequently accelerates the macroscopic phase transition. The results strongly demonstrate that the local lattice distortions due to the STEs are the trigger for the photoinduced phase transition.