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.