The Effect of Electric Field on the Frontier Orbitals of Organic Small Molecules: DFT Studies of Triphenylamine Derivatives

The effect of strong electric fields on four triphenylamine derivatives was investigated. Using the optimized structures performed via B3LYP/6-31+G(d,p) level of theory in vacuo, single-point energy calculations were performed in this work with CAM-B3LYP/6-311+G(d,p) with electric fields of strength 50x10-4au (c.a 2.57x10^9V/m) parallel and antiparallel to each of the x, y, and z axes. While fields in the y- and z- directions had little effect on molecular orbital (MO) contours, large changes occurred for fields in the x-direction, where the molecule lies. Additional calculations were performed at intermediate x-direction field strengths. The changes of the orbital contours are attributed both the pull of the field on the electrons in an orbital and to the rearrangement of molecular orbitals’ energies relative to one another. Furthermore, a linear relationship between MO energy and electric field strength was discovered, with deviations from linearity at high field strengths due to the near free electron characteristics. The maximum difference in HOMO and LUMO energy for the molecules under a more realistic field strength of 0.4x10^-4au was estimated to be about 0.022eV, which is insignificant to affect the open voltage of a solar cell device.