Electric field induced tuning of molecular conformation to acquire spintronics property in biphenyl systems

We have theoretically studied the effect of an external electric field on biphenyl, methylene substituted biphenyl monoradical and diradical systems. It has been found that the molecular conformation changes after the application of an external electric field. Thus, it is possible to tune molecular conformation reversibly only by external electrical stimuli. The HOMO-LUMO gap of the diradical reduces under an external electric field. The molecules with a low HOMO-LUMO gap can be used as unimolecular rectifiers if the HOMO and LUMO have a different spatial location on the molecule, or as a molecular conductor if the HOMO and LUMO are in the same spatial position. It has been observed that the diradical can be used as both a unimolecular rectifier and a molecular conductor depending upon the field strength. Now, the insulator molecule can be switched to a molecular rectifier or a molecular conductor and vice versa by an external electric field. The spin topology in a radical depends on the strength and direction of the applied electric field. Consequently, the extent of magnetic coupling in a diradical system changes with the external electric field. We have calculated the transmission spectra and I-V curve for the diradical at different dihedral angles. At a lower dihedral angle the diradical shows efficient spin filter behavior; within the range of bias voltage of 1 V and 1.5 V, the spin filtering efficiency of the diradical is achieved up to 99%. It is now possible to use a single molecule for multifarious applications like a unimolecular rectifier, spin filter and a molecular conductor depending upon the strength of the applied electric field.