Conjugated Polymers

Conjugated polymers are organic semiconducting materials that are revolutionising the world as we know it. Emerging as low-cost, flexible and sustainable alternatives to inorganic semiconductors, conjugated polymers have already shown incredible versatility in electronics, biocomputing, energy materials and biosensing applications. However, their widespread use is still hindered by their inherent heterogeneity, dispersity and tendency towards aggregation, all factors that make their chemical and structural characterisation extremely challenging (if not impossible) by traditional analytical techniques such as such as NMR, MS, XRD and SEC. In fact, already determining the exact sequence of a simple homopolymer can become difficult when the monomer reacts at the wrong position, and the picture becomes rapidly more complicated when dealing with the (multi)copolymers that are essential for high-performing materials.

This analytical challenge constitutes a significant (and widely recognised) limitation to progress in the field, having prevented the formulation of reliable structure-function relationships and hindered the improvement of the fabrication of these materials.

Our group has recently demonstrated that, by combining electrospray deposition (ESD) with scanning tunnelling microscopy (STM), it is possible to deposit intact conjugated polymers in ultrahigh vacuum (UHV) and to acquire sub-molecular resolved images, revealing their composition and structure at a level that is impossible with any other present analytical technique.

High-resolution STM images of C14DPPF-F polymers. (a) Assembly showing side chain interdigitation. (b) Direct visualisation of a homocoupling defect [1.]

This breakthrough resulted in the development of a transformative approach for the characterisation of conjugated polymers, that grants reliable access to a series of properties that are otherwise difficult to precisely access. This list includes, but is not limited to, the precise sequencing of the backbones of these macromolecules, the exact identification of chemical and structural defects and possible correlations of these defects, the full assembly patterns of the polymers in 2D, and the acquisition of complete mass distributions. Additionally, our technique allows us to design co-deposition experiments, where we can investigate in situ the interplay between conjugated polymers and their dopants.

High-resolution STM images of a self-assembled monolayer of (a) pBTTT [2.] and (b) IDT-BT. Geometry-optimised molecular models of the polymers are superimposed to the images

Key publications:

  1. Sequencing conjugated polymers by eye
    D. A. Warr, L. M. A. Perdigão, H. Pinfold, J. Blohm, D. Stringer, A. Leventis, H. Bronstein, A. Troisi, G. Costantini
    Sci. Adv. 4, eaas9543 (2018).
  2. The effect of glycol side chains on the assembly and microstructure of conjugated polymers
    S. Moro, N. Siemons, O. Drury, D.A. Warr, T.A. Moriarty, L.M.A. Perdigão, D. Pearce, M. Moser, R. Hallani, J. Parker, I. McCulloch, J. M. Frost, J. Nelson, G. Costantini
    ACS Nano 16, 21303 (2022).
  3. Regiochemistry-driven Organic Electrochemical Transistor Performance Enhancement in Ethylene Glycol Functionalized Polythiophenes
    R.K. Hallani, B.D. Paulsen, A.J. Petty II, R. Sheelamanthula, M. Moser, K.J. Thorley, W. Sohn, R.B. Rashid, A. Savva, S. Moro, J.P. Parker, O. Drury, M. Alsufyani, M. Neophytou, J. Kosco, S. Inal, G. Costantini, J. Rivnay, and I. McCulloch
    J. Am. Chem. Soc. 143, 11007 (2021).
  4. Anisotropy of charge transport in a uniaxially aligned fused electron deficient polymer
    M. Xiao, B. Kang, S.B. Lee, L.M.A. Perdigão, A.M.T. Luci, D.A. Warr, S.P. Senanaya, M. Nikolka, M. Statz, Y. Wu, A. Sadhanala, S. Schott, R. Carey, Q. Wang, M. Lee, C. Kim, A. Onwubiko, C. Jellett, H. Liao, W. Yue, K. Cho, G. Costantini, I. McCulloch, and H. Sirringhaus
    Adv. Mater. 32, 2000063 (2020).
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