Thiahelicene-based inherently chiral films for enantioselective electroanalysis

Abstract

Enantiopure inherently chiral films with helicoidal stereogenicity of outstanding enantiodiscrimination potentialities for chiral redox probes and as spin filters.

Widening the Scope of “Inherently Chiral” Electrodes: Enantiodiscrimination of Chiral Electroactive Probes with Planar Stereogenicity

“…In contrast, dichloromethane, while resulting in easier ferrocene compound solubility, would be less convenient for operating the oligo-(S a )-BT 2 T 4 films on account of lower stability of the latter. [41] Moreover, it would prevent observation of the reductive features, on account of CH 2 Cl 2 reduction at relatively mild potentials.…”

“…By electrooxidation it enables fast, reproducible electrode modification with films constituted by a mixture of open and cyclic inherently chiral electroactive oligomers (Figure 1), [35,45] resulting in effective enantiodiscrimination of chiral electroactive probes of different nature. [35][36][37][38] Remarkably, the same inherent chirality strategy has proved successful with other inherently chiral electrodeposited films, either based on different atropisomeric cores, i. e. bithiophene [39] and biindole, [40] or on a helical element as tetrathia [7]helicene [41] (carbohelicene films [46] could be also tested). It even held when implemented in ionic liquid media or related additives, again either on account of atropisomeric elements, i. e. bipyridinium [42] or bibenzimidazolium [43] salts, or of a helical tetrathiahelicene element.…”

“…In such selectors both chirality and main functional properties originate from the same element, coinciding in all so far considered examples with the main molecular backbone, which features a tailored torsion with a very high racemization barrier. [35][36][37][38][39][40][41][42][43][44] A thoroughly investigated model example is provided by the 2,2'-bis[2-(5,2-bithienyl)]-3,3'-bi-thianaphthene (BT 2 T 4 ) electroactive monomer, inherently chiral on account of its atropisomeric bibenzothiophene core (i. e., with sterically hindered rotation between its two halves). By electrooxidation it enables fast, reproducible electrode modification with films constituted by a mixture of open and cyclic inherently chiral electroactive oligomers (Figure 1), [35,45] resulting in effective enantiodiscrimination of chiral electroactive probes of different nature.…”

“…[44] Thus, the inherent chirality strategy has been shown to be of general character, a given selector (be it electrode surface or medium) being able to discriminate the enantiomers of redox probes with different chemical and electrochemical properties. [35][36][37][38][39][40][41][42][43][44] However, in such works only three out of the four kinds of rigid stereogenic elements (see key concepts and definitions at SI.1) have been considered in the chiral probes and/or chiral selectors, namely stereocenters (A), stereogenic axes (B), and helices (D, Figure 2).…”

Self‐Standing Membranes Consisting of Inherently Chiral Electroactive Oligomers: Electrosynthesis, Characterization and Preliminary Tests in Potentiometric Setups

“…[16,17] Large potential differences have been observed between enantiomers of various chiral probes in voltammetry experiments implementing inherent chirality at electrode j solution interphases by modifying achiral electrodes with enantiopure inherently chiral electroactive films electrodeposited from different heterocycle-based monomers with atropoisomeric cores (i. e. consisting of two moieties with hindered reciprocal rotation) [18][19][20][21][22] or with helical shape (i. e. tetrathiahelicene). [23] Among them, the parent and so far more extensively studied one is 2-[5-(2,5'-bithienyl)]thianaphthene BT 2 T 4 (Scheme 1) [18][19][20] consisting of a bibenzothiophene atropoisomeric core (with approximately 80°torsional angle and 167 kJ mol À 1 related energy barrier [18] ) and two bithiophene wings with homotopic α thiophene terminals available for oligomerization.…”