  We investigate the real-time dynamics of photoexcited electronic
instabilities in a charge-transfer system model, using the time-dependent
density matrix renormalization group method. The model of choice was the
quarter-filled one-dimensional extended Peierls-Hubbard Hamiltonian interacting
with classical few-cycle electromagnetic radiation. The results show that only
one electronic instability drives the main features of the photogenerated
time-dependent behavior. Indeed, the photoresponse of the system shows a large
enhancement of the $4k_F$ (bond and charge) instability whereas the $2k_F$
state remains largely unaffected. This conclusion holds regardless of the
nature of the optical excitations and whether the system is perturbed
resonantly or not. Our results suggest potential applications of
charge-transfer systems with slow phononic dynamics as optoelectronic switching
devices.
