Valence electrons are bound to atoms and molecules with energies of several electronvolts, corresponding to the energy of deep ultraviolet photons. They form chemical bonds, binding atoms together to build molecules. The equilibrium molecular structure is determined by the minimum of the energy of these electrons. If one of these electrons is excited, this equilibrium structure changes, setting the constituent atoms in motion, towards a new equilibrium structure. This change in structure may cause a change of biological function and/or chemical composition. It occurs on a femtosecond scale and can thus be captured by femtosecond laser pulses. However, this femtosecond structural dynamics may be preceded by much faster electronic motion. To what extent initial attosecond dynamics of valence electrons may affect subsequent changes in molecular structure and biological function is completely unclear and remains to be uncovered by attosecond spectroscopy.

Endowing the toolbox of attosecond technology with intense sub-femtosecond UV pulses and ultrawide-band shaped waveforms of laser light will open the door for a radically new approach to steering molecular structural dynamics: creating a localized electron wavepacket with a sub-fs UV pulse at a selected site of a biomolecule and subsequently steering it with the shaped electric field of a strong, synthesized light wave. The strong light field could possibly drive the electron to a selected location within the molecule, where it could break a bond and initiate rearrangement of molecular structure. This approach, if it were to work, would be radically new in that synthesized light fields would shape the density of bonding electrons in a molecule with attosecond resolution on a femtosecond time scale in a controlled way to make a desired unimolecular reaction to complete. Only experiments will tell us whether reality lives up to these visions.