Fluorination of 2,5-diphenyl-1,3,4-oxadiazole enhances the electron transport properties for OLED devices: a DFT analysis

In OLED devices 2,5-diphenyl-1,3,4-oxadiazole (PPD) is one of the most commonly used electron transport materials. Herein, equilibrium structures of PPD and its three fluorine-substituted derivatives, namely 2,5-bis(3-fluorophenyl)-1,3,4-oxadiazole (FPD), 2,5-bis(3,5-difluorophenyl)-1,3,4-oxadiazole (dFPD) and 2,5-bis(perfluorophenyl)-1,3,4-oxadiazole (pFPD) along with their corresponding molecular anions, have been optimized using DFT/B3LYP/6-31 + G(d,p) and DFT/ωB97XD/6-311 + G(d,p) techniques. The electro-optical parameters and global reactivity descriptors of all these molecules and molecular ions have been computed. Adiabatic electron affinity, vertical electron affinity and reorganization energy for estimating hole and electron transport have been obtained. Electronic transitions between molecular orbitals have been examined using UV-visible spectra. The addition of fluorine to PPD improves its electron affinity, which is advantageous for electron transport. The increased polarizability of fluorinated PPDs indicates that they are electronically more active than PPD molecules. Both the DFT methods reveal an almost similar pattern of electro-optical parameters, global reactivity descriptors and electron transport properties in fluorine-substituted PPD molecules.