A small Janus molecular dimer, as external electric field (Fz) manipulated both a molecular clam switch and a novel electric information storage unit, is found by quantum chemical computations for the first time. The molecular clam switching is intriguing and reversible. A critical Fz value of 95 × 10−4 au causes a dramatically open change in conformation from Closed form to Open form. And a small reversed electric field of Fz = −10 × 10−4 au performs a close change from Open form to Closed form. In the switching process, owing to the existence of a great electric dipole moment (μ) contrast between 0 and 22.13 D, the molecular clam switch may serve as an electric information storage unit. Gratifyingly, the reading, writing, and erasing of binary information on the electric information storage unit are easy. And further calculations show that Janus graphene fragment dimer can also serve as a molecular clam switch. Thus, this work proposes a new molecular switch prototype in the invention of artificial molecular machines, and a novel electric information storage unit in the field of molecular electronics.