Knowledge Bank

The formation of $\pi$-complexes between tetracyanoethylene (TCNE) and aromatic molecules results in intensely colored solutions. As a result of their study of the equilibrium constants and absorption spectra of these systems Merrifield and Phillips concluded that TCNE was the strongest $\pi$-acid examined up to that time. The spectra of some of these complexes in solution has now been studied as a function of pressure in the region 1-10,000 atmospheres. The peak frequency of the TCNE/benzene absorption band $(\nu o=26,000cm-1)$ shifts by about $1000cm-1$ to the red, while the intensity of this band increases by at least a factor of two. A more complete report on this and other systems will be given.