  The equilibration of macroscopic degrees of freedom during the fusion of
heavy nuclei, like the charge and the shape, are studied in the Time-Dependent
Hartree-Fock theory. The pre-equilibrium Giant Dipole Resonance (GDR) is used
to probe the fusion path. It is shown that such isovector collective state is
excited in N/Z asymmetric fusion and to a less extent in mass asymmetric
systems. The characteristics of this GDR are governed by the structure of the
fused system in its preequilibrium phase, like its deformation, rotation and
vibration. In particular, we show that a lowering of the pre-equilibrium GDR
energy is expected as compared to the statistical one. Revisiting experimental
data, we extract an evidence of this lowering for the first time. We also
quantify the fusion-evaporation enhancement due to gamma-ray emission from the
pre-equilibrium GDR. This cooling mechanism along the fusion path may be
suitable to synthesize in the future super heavy elements using radioactive
beams with strong N/Z asymmetries in the entrance channel.
