Electron-Induced Switching of the Supramolecular Chirality of Optically Active Polythiophene Aggregates

Abstract

A chiral regioregular polythiophene (PT), poly[3-[4-((R)-4-ethyl-2-oxazolin-2-yl)phenyl]thiophene] (poly-1), forms chiral aggregates which exhibit a unique induced circular dichroism (ICD) in the pi-pi transition region derived from the supramolecular chirality in the presence of various poor solvents or metal salts in chloroform. We report here that the chirality of such supramolecular aggregates can be switched ("on" and "off") through electron transfer. We have found that upon the addition of copper(II) trifluoromethanesulfonate [Cu(OTf)(2)] to the chiral aggregates of poly-1 in a chloroform-acetonitrile mixture, the ICD disappears because of the oxidative doping of the poly-1 main chain, while a further addition of amines such as triethylenetetramine (TETA) induces undoping of the poly-1 which results in the reappearance of the ICDs. Therefore, the supramolecular chirality of the poly-1 assemblies was reversibly controlled by the addition or removal of an electron from the poly-1 main chain. This may be the first example of a reversible supramolecular chirality switch on chiral PT aggregates. We investigated the mechanism of the chirality switch through the doping and undoping process on the polymer main chain by means of absorption and CD spectroscopies, ESR, cyclic voltammetry, X-ray diffraction, and AFM measurements.

Double screw-sense inversions of helical chiral-achiral random copolymers of fluorene derivatives in phase separating solutions

“…4 Chiroptical properties, such as circular dichroism (CD), optical rotation, and circular polarized luminescence, enrich the applications of these organic semiconductors as optical devices or sensors. [5][6][7][8][9] Optically active side chains may introduce chiroptical properties into conjugated polymers, but some polymers exhibit these properties only in films or phase separating solutions, [10][11][12][13] which indicates that intermolecular chiral interactions are necessary to induce the chiroptical properties in such conjugated polymers.…”

Characterization of thin films of regioregular poly(alkylthiophene)s bearing optically active substituents

“…Chiral poly(alkyl)thiophenes have been for years the subject of many studies [1][2][3][4][5][6][7][8][9][10] that have evidenced both the relevance of main chain regioregularity for achieving significant optical activity and the presence of remarkable conformational dissymmetry when the macromolecules are in the solid state or in microaggregates. In solution of a good solvent, polythiophenes bearing in the side chain a chiral alkyl group in one prevailing configuration do not display any optical activity arising from the presence of dissymmetric conformation of the backbone, as shown by circular dichroism (CD) spectra.…”

“…These CD bands are indicative of a chiral macromolecule arrangement of one prevailing chirality. This behaviour has been ascribed to the occurrence of a chiral supramolecular organization induced by the chiral groups located in the polythiophene side chains, and its relevance may be affected both by the nature of the substituents and the conditions under which the aggregation takes place [3,4,14].…”

Poly(p‐phenylene)‐type polymer composed of an (R,R)‐C2‐symmetric chiral recurring unit: Solution behavior, packing structure, and large circular dichroism observed with a film of the polymer

“…8,9 Recently, it has been recognized that optical properties, including nonlinear optical properties, 22 of a p-conjugated polymer in the solid state or in an aggregated state are affected not only by the electronic states of single polymer molecules but also by intermolecular electronic interactions (e.g., by the formation of an exciton). [22][23][24][25][26][27] The molecularly stacked structure depicted in Figure 2 seems to contribute to the strong CD effect in the film. The direct observation of De ¼ e R À e L (e R ¼ decadic molar absorption coefficient observed with right-CPL [CPL ¼ circulatory polarized light]; e L ¼ decadic molar absorption coefficient observed with left-CPL) with circularly polarized light generated with polarizing films was possible, and De of about 2000 M À1 cm À1 was obtained at 410 nm for the film of (R,R)-PH 2 Ph(9,10-OSiBu 3 ).…”

“…These data suggest the formation of colloidal particles of the polymer, which have an assembled packed structure like that shown in Figure 2, with the addition of methanol, a poor solvent. The formation of colloidal particles of p-conjugated polymers with the addition of methanol to chloroform solutions of p-conjugated polymers has been reported, 28,29 and changes in CD curves of polymer solutions depending on the kind of solvent have been reported; 9,26,27 the addition of a poor solvent is considered to bring about aggregationinduced CD effects. All these data support the notion that the assembled structure shown in Figure 2 causes an electronic interaction between the p-conjugated polymer molecules, and this brings about the large CD of the film and the colloidal solution.…”