Tuning the Quinoid versus
Biradicaloid Character of
Thiophene-Based Heteroquaterphenoquinones by Means of Functional Groups
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Abstract
A series of quinoidal bithiophenes (QBTs) with controlled
variations
in steric hindrance and electron activity of the substituents has
been synthesized. Evidence of their quinoidal versus biradicaloid
ground-state electronic character has been experimentally detected
and coherently identified as fingerprints by spectroscopic methods
such as NMR, UV–vis, multiwavelength Raman. From this analysis,
alkoxy groups have been shown to strongly affect the electronic structure
and the ground-state energy and stability of QBTs. Quantum-chemical
calculations correctly predict the experimental spectroscopic response,
even while changing the alkyl on phenone from a tertiary carbon atom
to secondary to primary toward an unsubstituted phenone, further confirming
the validity of the approach proposed. A control of the electronic
structure accompanied by negligible variations of the optical gap
of the molecules has thus been demonstrated, extending the potential
use of quinoidal species in fields ranging from photon harvesting
to magnetic applications