Mean-field electron-vibrational theory of collective effects in photonic organic materials: bistability

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated, and propagation of surface polaritons at the material/air interface was demonstrated. Here we develop a mean-field theory of light-induced optical properties of photonic organic materials taking the collective effects into account. The theory describes both a red shift of the resonance frequency of isolated molecules, according to the Clausius-Mossotti Lorentz-Lorentz mechanism, and the wide variations of their spectra related to the aggregation of molecules into J- or H-aggregates. We show that the experimental absorption spectra of H-aggregates may be correctly described only if one takes both mechanisms into account. The bistable response of organic materials in the condensed phase has been demonstrated using the electron-vibrational model. We show that using molecules with long-living triplet state T1 near excited singlet state S1, and fast intersystem crossing S1->T1 enables us to diminish CW light intensity needed for observing bistability below the damage threshold of thin organic films.