Hybrids of Semiconducting Single-walled Carbon Nanotubes and Tailored Conjugated Polyelectrolytes as Selective Sensor Materials
Preparatory and Physical Chemistry of Polymers
Final Report Abstract
The availability of large amounts of well-defined semiconducting single-walled carbon nanotubes (SWNTs) enables their application in reproducible, solution-processed devices such as optical and electronic sensors. In this project we synthesized a wide range of tailored conjugated polymers (typically polyfluorene copolymers) and conjugated polyelectrolytes with specific functional groups and combined them with pre-sorted, semiconducting (6,5) SWNTs via an optimized polymerexchange protocol. These polymer/SWNT hybrids were investigated in dispersion and in thin films with respect to their optical (near-infrared photoluminescence) and electronic (conductivity) responses to various stimuli (e.g., temperature, UV light) and analytes (e.g., metal ions). While not all of the newly synthesized polymers were able to re-disperse nanotubes in significant amounts and some did not show a significant synergistic effect in a hybrid with SWNTs (e.g., thermo-responsive PNIPAM-functionalized polyfluorenes), a number of polymer/nanotube combinations showed novel and even unexpected effects that could be employed for sensors. We showed that wrapping (6,5) SWNTs with anionic conjugated polyelectrolytes in methanol led to slight p-doping in air and prevented energy transfer from the polymer to the nanotubes, while cationic polyelectrolytes and various other polyfluorenes clearly showed very efficient and fast energy transfer (as observed via photoluminescence excitation-emission maps and transient absorption). The energy transfer from the anionic polyelectrolyte could, however, be restored by adding a mild reducing agent, thus indicating an electron exchange mechanism between polymer and nanotube. The functionalization of a polyfluorene polymer backbone with photochromic spiropyran side groups and wrapping of (6,5) SWNTs with it enabled deposition of photo-responsive thin films that showed a persistent and additive increase of conductivity upon irradiation with ultraviolet (UV) light in air due to the transformation of spiropyran into merocyanine with a much larger dipole moment. In the presence of oxygen, the created merocyanine groups led to significant p-doping of the nanotubes (as confirmed by charged exciton (trion) emission) proportional to the total light dose, which was however easily reversed by a short and moderate heating step. Hence, these thin hybrid films could be used in UV- dosimeters or optical memory elements. Surprisingly, we also found that networks of semiconducting (6,5) SWNTs wrapped with the standard commercial polyfluorene for selective nanotube dispersion, which contains a bipyridine unit, could be applied directly in water-gated transistors for the detection of copper(II)-ions. The observed specific interaction of copper-ions with the nanotube/polymer hybrids and associated concentrationdependent voltage shifts of the transfer characteristics could likewise be used to quantitatively detect biologically and environmentally relevant pyrophosphonates and phosphonates through competitive copper binding. Lastly, the hydrophobic alkyl side chains of the typical wrapping polymers were replaced by hydrophilic tetraethylene glycol side chains, which improved long-term stability of the nanotube dispersions and increased the volumetric capacitance and thus also the transconductance of watergated transistors with aerosol printed networks of polymer-wrapped (6,5) nanotubes, making their performance competitive to state-of-the-art semiconducting polymers for bioelectronics.
Publications
- Doping-Dependent Energy Transfer from Conjugated Polyelectrolytes to (6,5) Single-Walled Carbon Nanotubes. J. Phys. Chem. C 2019, 123, 22680-22689
Balcı Leinen, M.; Berger, F. J.; Klein, P.; Mühlinghaus, M.; Zorn, N. F.; Settele, S.; Allard, S.; Scherf, U.; Zaumseil, J.
(See online at https://doi.org/10.1021/acs.jpcc.9b07291) - Spiropyran-Functionalized Polymer–Carbon Nanotube Hybrids for Dynamic Optical Memory Devices and UV Sensors. Adv. Electron. Mater. 2020, 6, 2000717
Balcı Leinen, M.; Klein, P.; Sebastian, F. L.; Zorn, N. F.; Adamczyk, S.; Allard, S.; Scherf, U.; Zaumseil, J.
(See online at https://doi.org/10.1002/aelm.202000717) - (2021), Konjugierte Polymere für Sensorikanwendungen, PhD Thesis, Bergische Universität Wuppertal
P. Klein
(See online at https://doi.org/10.25926/6zwv-7b83) - Charge Transfer from Photoexcited Semiconducting Single-Walled Carbon Nanotubes to Wide- Bandgap Wrapping Polymer. J. Phys. Chem. C 2021, 125, 8125-8136
Kuang, Z.; Berger, F. J.; Lustres, J. L. P.; Wollscheid, N.; Li, H.; Lüttgens, J.; Balcı Leinen, M.; Flavel, B. S.; Zaumseil, J.; Buckup, T.
(See online at https://doi.org/10.1021/acs.jpcc.0c10171) - Fluorescence Studies on a Thermoresponsive PNIPAM-Polyfluorene Graft Copolymer. Macromolecules 2021, 54, 7612-7620
Cunha, C.; Klein, P.; Rosenauer, C.; Scherf, U.; Seixas de Melo, J. S.
(See online at https://doi.org/10.1021/acs.macromol.1c00827) - Organic Synaptic Diodes Based on Polymeric Mixed Ionic-Electronic Conductors. Adv. Electron. Mater. 2021, 7, 2100866
Gärisch, F., Ligorio, G., Klein, P., Forster, M., Scherf, U., List-Kratochvil, E. J. W.
(See online at https://doi.org/10.1002/aelm.202100866)
