Impact of Orbital Hybridization at Molecule–Metal Interface on Carrier Dynamics

The orientation of a molecule on a metal surface can impact the performance of electronic devices fabricated from organic materials. This orientation effect of physiosorbed or weakly chemisorbed molecules has been widely debated, and its origin remains unknown because methods to investigate the weak interaction at the molecule/inert-metal interface have been limited. Here, it is shown via spectroscopy and density functional calculations that molecule/metal orbital hybridization, which is determined by the molecular orientation, is an identity of the orientation effect dictating the carrier dynamics at the interface. Nanoscale model interfaces, where molecules were weakly chemisorbed on a metal, made it possible to visualize the orientation-dependent shift of the electronic state. The transient absorption spectroscopy and scanning tunneling spectroscopy of porphyrin derivative coordinated on gold nanoparticle demonstrated that the orbital hybridization dictates the interfacial carrier dynamics. This new understanding of the molecule/metal interfaces will enable functional-molecule designs based on the cross-materials orbital hybridization for various devices.