Bis(paraxylylenyl) (2) is formed as the primary photoproduct of [2.2]paracyclophanene (1) and can be stabilized in rare gas matrices at 10 K. In this study we assess the biradical character of 2 on the basis of our reassigned UV photolysis spectra as well as correlated ab initio geometry optimizations. The time evolution of the absorption peaks reveals that two photoproducts are formed from 1. We assign the long-wavelength absorption at 600 nm to a higher energy biradical structure which is stabilized by the rigid matrix environment.
Henseler, D., & Hohlneicher, G. (1999). How biradicaloid is bis(paraxylylenyl)? A spectroscopical and theoretical study. In Journal of Molecular Structure (Vol. 480–481, pp. 515–518). https://doi.org/10.1016/S0022-2860(98)00733-9