Theoretical investigation of excitation states of tetracyanoethylenen−-biphenylene (n=0,1,2) system

In this work, the author pays attention to the geometries and vertical excited states of the tetracyanoethylenen−-biphenylene (TCNEn−-BP, n=0,1,2) systems. The optimal geometries are obtained by MP2/6-31G* method. The excited states of the systems are optimized at the level of CIS/6-31++G**. Based on the theoretical calculations, the trichromic change arising from the neutral complex formation, the anion radical generation, and the dianion complex formation has been explained. By using the self-consistent reaction field (SCRF) method, the solvent effects on charge transfer absorption have been investigated. Theoretical calculations predict a red shift of the electronic absorption in polar solvent for TCNE-BP and a blue shift for TCNE2−-BP. It is concluded that TCNE2−-BP possesses different geometry and spectrum from those of the neutral and anion complexes.