Detailed structural information of conjugated polymers revealed by high resolution scanning tunnelling microscopy Paola Mantegazza 1 , Stefania Moro 1 , Xiaocui Wu 2 , Jochen Vanderspikken 3 , Wouter Maes 3 Giovanni Costantini 1,2 1 School of Chemistry, University of Birmingham, UK, 2 Department of Chemistry, University of Warwick, UK, 3 Institute for Materials Research (IMO), Hasselt University, Belgium Among organic semiconductors, conjugated polymers (CPs) have attracted considerable attention, due to their exceptional conductive properties, combined with mechanical flexibility and low-cost processability. These make CPs promising candidates for a broad variety of applications, including optoelectronics, thermoelectrics, sensors and bioelectronic devices [1-2]. The combination of electrospray deposition (ESD) [3] with scanning tunnelling microscopy (STM) in ultrahigh vacuum, recently developed in the Costantini Group [4], allows one to obtain detailed, molecular scale information about the structure, conformation and assembly of surface-adsorbed conjugated polymers at a level that is not possible with any other current analytical technique. The electrospray ionisation process enables the controlled and intact soft-landing of sub-monolayer coverages of CPs onto atomically clean and flat single crystal surfaces, while preserving the CP original sequence and structure. The resulting surfaces are analysed by high-resolution STM, which provides direct evidence about the preferential assembly configurations of CPs, their stacking distances, the polymer mass distributions, the exact backbone sequences and the side chain conformations [5]. Here, we focus on the benchmark polymer pBTTT [6], which has been reported to have a (semi)crystalline microstructure and exhibits a high charge carrier mobility [7]. In particular, this study aims at comparing two variants of pBTTT, with mixed alkyl and alkoxy side chains, synthesised by the traditional Stille polymerisation as well as by an alternative oxidative homopolymerisation method, that is expected to produce less defects. This type of in-depth structural characterisation – which cannot be achieved by the standard analytical techniques used in polymer science – is essential in determining reliable structure-function relationship and paves the way to developing new, greener, more sustainable and improved synthetic polymerisation strategies for this essential class of functional materials. References 1. Reynolds, J. R., et al. , CRC press, (2019).
2. Fratini, S., et al ., Nat. Mater. 19 , 491–502 (2020). 3. O'Sullivan, M. C. et al ., Nature 469 , 72–75 (2011). 4. Warr, D. A. et al. , Sci. Adv. 4 , 0–6 (2018). 5. S. Moro, et al ., ACS Nano. 16 , 12, 21303-21314 (2022). 6. R. Joseph Kline, et al. , Macromolecules 40 , 7960–7965, (2007). 7. Rawad K. Hallani et al ., ACS Journal 143 , 11007–11018, (2021).
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