Tetrakis (1,3-benzodithiol-2-ylidene) cyclopentyl Cations with Light Absorption in a Near Infrared.

The titled cations exhibited remarkably long wavelength absorptions reaching to a near infrared above 750 nm. The cause of this deep coloration has been clarified, which is ascribed to such a stabilization of electronically-excited biradicalic structures beyond expectation, as to participate in the ground states of the cations albeit in a very small amount (10−3–10−2%).