Unique Orbital Interactions in the Ground and Electronically Excited States of Biradicals Brought about by the Existence of “Twisted π-Space”

Abstract

The six-membered cyclic 1,4-radical cation 2 •+ forms a “twisted π-space” due to noncoplanarity of the cumyl radical 3 • and cumyl cation 3 + originating from a chair conformation of the central cyclohexane ring system. The results of substituent effects on absorption wavelengths of 2 •+ indicate that both through-space (TS) and through-bond (TB) orbital interactions operate in a “twisted π-space” of 2 •+, resulting in the theoretically maximal orbital interactions between 3 • and 3 +. An operation of similar TS and TB orbital interactions is also suggested in the excited-state biradical 1 2 ••* by the results of substituent effects on thermoluminescence wavelengths.