The self-trapping by the nondiagonal particle-phonon interaction between two quasi-degenerate energy levels of exitonic subsystem, is studied. We propose this is realized in charge transfer exciton, where the directions of the poralization give the quasi-degeneracy, as in quasi-one-dimensional compound A-PMDA. We present a quantitative theory for the optical properties (light absorption and time-resolved luminescence) of the resonating states, which gives a consistent resolution for the long-standing puzzles in A-PMDA.
Photoinduced coherent oscillations in the one-dimensional two-orbital Hubbard model