Thia-Bridged Triarylamine[4]helicene-Functionalized Polynorbor­nenes as Redox-Active pH-Sensitive Polymers

Abstract

A series of thia-bridged triarylamine[4]helicene-functionalized polynorbornenes P1, P2, and P3 were synthesized via ring-opening metathesis polymerization (ROMP). The polymers obtained undergo a reversible one-electron oxidation, in both solution and solid state, responding to the pH changes in the surrounding medium showing a clear reversible electrochromic behavior.

A Lewis Base Hydrogen Bond Donor (LB/HBD) Organocatalytic Approach to Dithiabridged Triarylamine Hetero[4]helicenes

“…We have well demonstrated that at low pH the oxidation potential of helicenes 1 becomes low enough to allow the mono-electronic oxidation to the corresponding radical cations 1 + * by atmospheric oxygen. [7,8] Thus, we switch to HFIP as a suitable HBD. Mixing 2 a in HFIP (25 mg in 250 μL) at rt for 48 h, caused the formation of small amounts of 1 a.…”

“…[3][4][5][6][7][8][9] Additionally, derivatives 1 demonstrate a rich redox chemistry and, for example, the easy access to the corresponding, exceptionally stable, chiral radical cations by one-electron oxidation has been well documented. [4,7,9,10] Hetero [4]helicenes 1 can be prepared [3][4][5][6][7][8][9][10][11] from mono-N-thiophthalimido sulfenylated N-arylphenothiazines 2, or from bis-N-thiophthalimido sulfenylated triaryl amines 3. [12] These derivatives react with over stoichiometric amounts of a Lewis Acid (LA, typically AlCl 3 ), to give the helical bis-phenothiazine skeleton via one, or two, intramolecular electrophilic aromatic substitution (iS E Ar) as depicted in Scheme 1 for the preparation of hetero [4]helicenes 1 a and 1 b from 2 a and 3 a respectively.…”

“…We have developed the chemistry of dithiabridged triaryl amine hetero[4]helicenes 1 (see Scheme 1) as a peculiar class of geometrically stable [4]helicenes with racemization barriers higher than 32 kcal/mol [3] . The structure of these compounds can be described as a bis‐phenothiazine with an aryl ring and a nitrogen atom in common, forced in a helical skeleton by the four long carbon‐sulfur bonds [3–9] . Additionally, derivatives 1 demonstrate a rich redox chemistry and, for example, the easy access to the corresponding, exceptionally stable, chiral radical cations by one‐electron oxidation has been well documented [4,7,9,10] …”

SET and HAT/PCET acid‐mediated oxidation processes in helical shaped fused bis‐phenothiazines

“…Helical shaped bis-phenothiazines, like derivatives 1-9 prepared for this study, have found interesting opportunities in material science [11,16] and a detailed quantitative investigation of their red-ox one-electron properties appeared a mandatory step to underpin their peculiar characteristics.…”

“…[10] This has paved the way to valuable applications, such as the preparation of redox active pH-sensitive polymers. [11] Additionally, organic radicals have been proposed as building blocks for several multifunctional devices, [12,13] including spin filters for molecular spintronic devices, [14,15] because of their relatively long spin coherence length. Thus, the possibility of tailoring the spin filtering exploiting the chiral induced spin selectivity (CISS) effect of the exceptionally stable radical cations obtained from compounds possessing skeleton C, is under development.…”