Stable Thiele’s Hydrocarbon Derivatives Exhibiting Near-Infrared Absorption/Emission and Two-Step Electrochromism

We
report synthesis and characterization of near-infrared (NIR)-absorbing/emitting
Thiele’s hydrocarbon derivatives, in which four aryl groups
are bridged to a quinodimethane skeleton. The quinoid structure of
the bridged-tetra-aryl-p-quinodimethanes (BTAQs)
was confirmed by spectroscopic, X-ray crystallographic, and computational
methods. Although quinodimethane derivatives with a small HOMO–LUMO
energy gap often exhibit biradical character, BTAQs showed no biradical
character. Instead, they exhibited two-step near-infrared electrochromism.
The donor/acceptor properties of the aryl groups were found to play
a key role in the unique properties of BTAQs.