Three-State Switching of an Anthracene Extended Bis-thiaxanthylidene with a Highly Stable Diradical State

A multistable molecular
switching system based on an anthracene-extended
bis-thiaxanthylidene with three individually addressable states that
can be interconverted by electrochemical, thermal, and photochemical
reactions is reported. Besides reversible switching between an open-shell
diradical- and a closed-shell electronic configuration, our findings
include a third dicationic state and control by multiple actuators.
This dicationic state with an orthogonal conformation can be switched
electrochemically with the neutral open-shell triplet state with orthogonal
conformation, which was characterized by EPR. The remarkably stable
diradical shows kinetic stability as a result of a significant activation
barrier for isomerization to a more stable neutral closed-shell folded
geometry. We ascribe this activation barrier of ΔG⧧(293 K) = 25.7 kcal mol–1 to
steric hindrance in the fjord region of the overcrowded alkene structure.
The folded closed-shell state can be converted back to the diradical
state by irradiation with 385 nm. The folded state can also be oxidized
to the dicationic state. These types of molecules with multiple switchable
states and in particular stable diradicals show great potential in
the design of new functional materials such as memory devices, logic
gates, and OFETs.