Utilization of asymmetrical electron transport as strategy for modelling and design of efficient single molecule diodes: A DFT investigation

Abstract

Present study investigates two organic molecular systems, p − Sexiphenyl − σ − TCNQ and p − Sexiphenyl − σ − NTCDA, for possible use as single molecule diodes based on the Aviram and Ratner concept of D − σ − A model. Quantum chemical simulations were performed under the density functional theory (DFT) approach, using B3LYP functional and 6 − 31G(d,p) basis set. Calculated values of HOMO − LUMO gap, dipole moment and natural charges have been used for analysis. Results have been analyzed for both systems at different values of applied electric fields in both directions along the molecular axis. The results show that, HOMO − LUMO gap in forward biased condition (D to A direction of electric field) shrinks on increasing the electric field strength, whereas, in the reverse biased condition (A to D direction of electric field) the HOMO − LUMO gap increases until the breakdown condition is achieved. If the electric field strength is further increased in reverse bias condition, behaviour similar to avalanche breakdown is observed.