Three-stage binary switching of azoaromatic polybase.

An OFF-ON-OFF-type three-stage binary switching was realized with an azoaniline-based polybase 1. The optical properties of 1 and [1·2H](2+) are essentially indistinguishable to the naked eye but distinctively different from those of [1·H](+) to produce an unusual bell-shaped response as a function of protonation state; the underlying molecular mechanism was unraveled by a combination of experimental and DFT computational studies.