High order harmonics are generated when molecules are ionized by an intense femtosecond laser pulse. The freed electron is accelerated in the external driving electric field and, because of the periodic oscillation of this field, is brought back to the parent ion, where it can recombine and give rise to the emission of an XUV photon. This XUV harmonic radiation has been shown to contain information on the electronic structure of the molecule, which can be interpreted as a picture of the molecular orbital. The idea of exploiting high order harmonic generation (HHG) for the tomographic reconstruction of the electronic structure in molecules was first introduced in 2004 for nitrogen molecules. Up to now, despite several attempts, a successful investigation of the molecular structure by HHG was still lacking for molecules more complex than N2. Recently I demonstrated a new experimental and theoretical approach for extending the imaging of molecular orbitals to a triatomic molecule. However, the real breakthrough in molecular imaging, namely the achievement of a time-resolved tomography providing a movie of the wavefunction of molecules while undergoing structural changes, has not yet been attempted.The goal of this project is to develop time-resolved HHG tomography for real-time imaging of evolving electronic structure in complex molecules undergoing electronic or vibrational excitation.The key idea of UDynI is to use a mid-IR (1.3-1.8 µm) few-cycle laser source to drive the harmonic generation process. This will allow tackling the limitations that prevented up to now the realization of time-resolved tomography of complex molecules during molecular rearrangement.I will mainly consider organic molecules, such as hydrocarbons, hydrocarbons with functional groups and aromatic hydrocarbons, which are interesting precursors for the study of biological functions.