Laser control of double proton transfer in porphycenes: towards an ultrafast switch for photonic molecular wires

Electronic excitation energy transfer along a molecular wire depends on the relative orientation of the electronic transition dipole moments of neighboring chromophores. In porphycenes, this orientation is changed upon double proton transfer in the electronic ground state. We explore the possibility to trigger such a double proton transfer reaction by means of an infrared pump-dump laser control scheme. To this end, a quantum chemical characterization of an asymmetrically substituted porphycene is performed using density functional theory. Ground state geometries, the topology of the potential energy surface for double proton transfer, and (hbox{S}_0rightarrowhbox{S}_1) transition energies are compared with the parent compound porphycene and a symmetric derivative. Employing a simple two-dimensional model for the double proton transfer, which incorporates sequential and concerted motions, quantum dynamics simulations of the laser-driven dynamics are performed which demonstrate tautomerization control. Based on the orientation of the transition dipole moments, this tautomerization may lead to an estimated change in the Förster transfer coupling of about 60%.