Adsorption of PTCDA on NaCl Surfaces with Color Centers: Charge Transfer and Formation of Radical Ions

Defect centers in crystalline surfaces significantly influence the local electronic structure and thus the reactivity. We investigated the interaction between surface color centers in the NaCl(100) surface with adsorbed 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) using dielectric-dependent global hybrid density functionals. A strong interaction between the unpaired electron in the color center and PTCDA is observed leading to a single electron transfer and the formation of a PTCDA radical anion. This leads to a stronger interaction between the molecule and the surface, resulting in a narrowing of the electronic gap, higher adsorption energy, and stronger distortion of the molecule. The effect has a significant influence on the IR spectrum of PTCDA.