Delineating Poly(Aniline) Redox Chemistry by Using Tailored Oligo(Aryleneamine)s: Towards Oligo(Aniline)‐Based Organic Semiconductors with Tunable Optoelectronic Properties

Abstract

The simple and elegant Buchwald-Hartwig cross-coupling reaction has been used to synthesise a designed range of new aniline-based tetramers in one step, and without the need for protecting groups. Variation of the central aromatic ring has provided the opportunity to carefully tune the optoelectronic properties in this series, thus enabling a structure-activity relationship study by using a range of photophysical and electrochemical techniques. As a result, the long-proposed sequences of electron-electron (EE) and electron-chemical (EC) processes that support the complex redox and proton-transfer reactions involved in the well-known switching of redox states of poly- and oligo(aniline)s are revealed here for the first time. We also present the initial results from time-dependent DFT calculations to clarify the optoelectronic behaviour of these oligomers. The dc-conductivity measurements of conducting thin films of this series, doped with the prototypical poly(aniline) protonating agent D,L-camphor-10-sulfonic acid (CSA), externally plasticised with triphenyl phosphate (TPP), and processed from m-cresol (MC) solutions, are also presented.

Exploring Redox States, Doping and Ordering of Electroactive Star‐Shaped Oligo(aniline)s

“…By coupling a star‐shaped tribromide 1 with dianiline 2 (Scheme 1) using the Buchwald–Hartwig reaction,14 a simple star‐shaped oligo(aniline) was obtained in its fully reduced state in high yield (see the Supporting Information for all experimental and analytical details). The product, 1,3,5‐tris(4‐dianilinophenyl)benzene, is abbreviated hereafter to TDPB .…”

“…Time‐dependent density functional theory (TD‐DFT) simulations are very useful for identifying electronic states of oligo(aniline)s in solution that are difficult to isolate or characterise in full 13, 14…”

“…Modifying the periphery of oligo(aniline)s provides a further route to tune self‐assembly: attachment of alkyl tails promotes the formation of ordered conducting thin films,12 while the addition of a surfactant head‐group to tetra(aniline) causes it to self‐assemble into conducting nanowires in water 13. Optoelectronic properties can also be tuned using an oligomer approach: variation of the aromatic ring system at the centre of the molecule leads to systematic changes of optoelectronic properties 14. Finally, the presence of external templates such as graphene has been used to direct the crystallization of oligo(aniline)s vertically, orienting the molecules into stacks and increasing the conductivity by an order of magnitude 15.…”

Structured oligo(aniline) nanofilms via ionic self-assembly

“…30 The dopant bis(ethyl hexyl)phosphate (BEHP; 97%) and tetrahydrafuran (THF; analytical grade) solvent were obtained from Sigma-Aldrich and used as received. Silicon wafers were purchased from University Wafers and cleaned by sonication for 5 minutes each in acetone, ethanol and Millipore water before rinsed with THF and dried under nitrogen flow.…”

Conductive‐AFM Patterning of Organic Semiconductors

“…[ 21 ] It is possible to fi ne-tune the optoelectronic properties of tetra(aniline) derivatives, and higher oligomers, simply through modifi cation of the central unit and variation of the end-group functionalization. [ 22 ] Similar to PANI, these oligomeric materials can be reversibly switched (doped) from their conductive emeraldine salt (ES) state to either the nonconductive fully reduced leucoemeraldine base (LEB) or emeraldine base (EB) states through redox, and acid-base chemistry, respectively. [ 23 ] An extensive range of possible inorganic and organic acid dopants exists, with the latter able to simultaneously act as dopants and plasticisers.…”