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

Abstract

Using a simple π-conjugated trimer, EDOT-phenylene-EDOT (where 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 non-covalent contacts (where X = H or F). Such non-bonding 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 XRD studies, cyclic voltammetry, absorption spectroscopy and density functional theory calculations to identify the dominant non-covalent 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 non-covalent interactions and their effects persist in polymers. Our findings show that hydrogen bonding and halogen bonding feature in these molecules and their corresponding polymers.

Quantifying Planarity in the Design of Organic Electronic Materials

“…Overall, these results are supported by previous empirical findings, [58, 59] and the quantification paves the way for rational exploitation of substituents in a wide range of molecular designs.…”

“…Nonetheless,a lignment of the side-chains in the solid state may occasionally contribute to the planarization of the conjugated backbone through packing effects. [57] Overall, these results are supported by previous empirical findings, [58,59] and the quantification paves the way for rational exploitation of substituents in aw ide range of molecular designs.…”

Crucial Role of Fluorine in Fully Alkylated Ladder-Type Carbazole-Based Nonfullerene Organic Solar Cells

“…crystallinity and facilitate charge transport. [22][23][24][25][26][27][28] Moreover, comparing the 1,1-dicyanomethylene-3-indanone (IC) endgroup with its fluorinated derivative 2-(5,6-difluoro-3oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-4F), the stronger electron-withdrawing effect of the latter can enhance intramolecular charge transfer (ICT) in NFA materials resulted in a red-shift of the absorption spectra of NFAs to the near-IR region, thus enhancing device photocurrent. Several studies have demonstrated that OSCs based on ladder type NFAs with fluorinated endgroups show improved device performance than those based on non-fluorinated counterparts.…”

Unifying Charge Generation, Recombination, and Extraction in Low‐Offset Non‐Fullerene Acceptor Organic Solar Cells

“…In fact, while there are several studies in the literature that have utilized ssNMR to characterize blend morphologies for polymers or polymer:fullerene blends, [23,[31][32][33][34][35][36][37] the application of ssNMR techniques to characterize structurally similar polymer:NFA blends is limited. [11,38] While fluorination in conjugated systems has been shown to result in improved molecular level interactions and charge transport by many previous reports, [29,[39][40][41] this is the first time that crucial differences such as π-π interactions and local ordering in polymer:NFA blends could also be resolved via ssNMR. Here, we posit that low energetic offset polymer:NFA systems with low voltage losses are key in attaining high PCEs -but not without a caveat.…”