Molecule Isomerism Modulates the Diradical Properties of Stable Singlet Diradicaloids

Inclusion of quinoidal
cores in conjugated hydrocarbons is a common
strategy to modulate the properties of diradicaloids formed by aromaticity
recovery within the quinoidal unit. Here we describe an alternative
approach of tuning of diradical properties in indenoindeno­dibenzo­thiophenes
upon anti → syn isomerism
of the benzothiophene motif. This alters the relationship of the S
atom with the radical center from linear to cross conjugation yet
retains the same 2,6-naphtho conjugation pattern of the rearomatized
core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic,
theoretical, and magnetic measurements, showing that these systems
are stable open-shell singlet diradicaloids that only access their
triplet state at elevated temperatures.