11,11'-Biindeno[2,1-a]azulenylidenes: potassium tert-butoxide-promoted homocoupling of 11H-indeno[2,1-a]azulenes and their optical properties.

t-BuOK-promoted homocoupling of 11H-indeno[2,1-a]azulenes enables direct synthesis of twisted 11,11'-biindeno[2,1-a]azulenylidenes. X-ray analysis confirms nonplanar central CC units, yet the π-systems retain strong electronic communication, visible-to-near-infrared absorption, and acid-responsive halochromism, highlighting torsional distortion as a design element in nonbenzenoid π-systems.