Phase transformations induced by short optical pulses is a new mainstream in studies of cooperative electronic states. We present a semi-phenomenological modelling of spacio-temporal effects expected when optical excitons are coupled to a symmetry breaking order parameter as it happens in organic compounds with neutral-ionic phase transitions. In our scenario, after a short initial pulse of photons, a quasi-condensate of excitons appears as a macroscopic quantum state which then evolves interacting with other degrees of freedom prone to instability. This coupling leads to self-trapping of excitons akin to self-focusing in optics. The locally enhanced density of excitons can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains which evolve through dynamical phase transitions and may persist even after the initiating excitons have recombined.
A conceptual complication appears when both the excitation and the long range ordering are built from the intermolecular electronic transfer, like for the charge-transfer exciton in neutral-ionic systems. We describe both thermodynamic and dynamic effects for the phase transition using the concept of the Excitonic Insulator.