Density functional study of triazole and thiadiazole systems as electron transporting materials

Density functional theory has been used for the calculation of electronic structures, vertical electron affinities and intramolecular reorganization energies for bis-aryl substituted triazole and thiadiazole. The results obtained on the basis of the theoretical calculations indicate that the HOMO and LUMO energies of the substituted molecules can be tuned by changing the substituents as well as by changing the center atom. These changes lead to energy shifts in the order of 2-2.5 eV. The calculation and comparison of vertical electron affinities and intramolecular reorganization energies confirm that thiadiazole systems are interesting for electron transport properties. Taking a lesson from these substitutions, we further model the systems by twisting the molecular units along the central dihedral angle starting from the ideal structure and compare their HOMO-LUMO gap, electron affinity and reorganization energy. We find that by having simple substituents at proper positions one can control the reorganization energy, which in turn indicates that electron transport properties can be tuned.