Fluoreno[2,1-]fluorene: an -naphthoquinodimethane-based system with partial diradical character

Fluoreno[2,1- a ]fluorene, a molecule comprising fused ortho -quinodimethane units in a 1,5-napthoquinodimethane core, has been prepared and investigated with spectroscopy (UV-Vis-NIR, 1 H-NMR and Raman), SQUID magnetometry, spectroelectrochemistry and quantum chemistry. While para -quinodimethanes with a 2,6-substitution pattern exist as closed-shell species and meta -quinodimethanes with 2,7-substitution favour a ground electronic state with very large diradical character, our 1,5-substituted ortho -naphthoquinodimethane-based system exhibits an intermediate degree of diradical character. An ortho -naphtho diradical! Quinoidal forms in para - and meta -patterns lie at the extremes for closed-shell and diradical forms in fluorenofluorenes, respectively. ortho -Conjugation gives an intermediate case with partial diradical character.