Noncovalent Close Contacts in Fluorinated Thiophene–Phenylene–Thiophene Conjugated Units: Understanding the Nature and Dominance of O···H versus S···F and O···F Interactions with Respect to the Control of Polymer Conformation

Using
a simple π-conjugated trimer, EDOT–phenylene–EDOT
(EDOT = 3,4-ethylenedioxythiophene), we evaluate the effect that fluorine
substituents have upon changes in conformation, conjugation, and oxidation
potentials in π-conjugated structures. These variations are
assessed as a function of the fluorine atom’s propensity to
feature in hydrogen and/or halogen bonding with other heteroatoms.
The molecular motif was chosen because the EDOT unit presents the
possibility of competing O···X or S···X
noncovalent contacts (where X = H or F). Such nonbonding interactions
are acknowledged to be highly influential in dictating molecular and
polymer morphology and inducing changes in certain physical properties.
We studied four compounds, beginning with an unsubstituted bridging
phenylene ring and then adding one, two, or four fluorine units to
the parent molecule. Our studies involve single-crystal X-ray diffraction
studies, cyclic voltammetry, absorption spectroscopy, and density
functional theory calculations to identify the dominant noncovalent
interactions and elucidate their effects on the molecules described.
Experimental studies have also been carried out on the corresponding
electrochemically synthesized polymers to confirm that these noncovalent
interactions and their effects persist in polymers. Our findings show
that hydrogen bonding and halogen bonding feature in these molecules
and their corresponding polymers.