  We define, compute and analyze the nonequilibrium differential optical
conductivity of the one-dimensional extended Hubbard model at half-filling
after applying a pump pulse, using the time-dependent density matrix
renormalization group method. The melting of the Mott insulator is accompanied
by a suppression of the local magnetic moment and ensuing photogeneration of
doublon-holon pairs. The differential optical conductivity reveals $(i)$
mid-gap states related to parity-forbidden optical states, and $(ii)$ strong
renormalization and hybridization of the excitonic resonance and the absorption
band, yielding a Fano resonance. We offer evidence and interpret such a
resonance as a signature of nonequilibrium optical excitations resembling
excitonic strings, (bi)excitons, and unbound doublon-holon pairs, depending on
the magnitude of the intersite Coulomb repulsion. We discuss our results in the
context of pump and probe spectroscopy experiments on organic Mott insulators.
