Electroactive Metal Complexes Covalently Attached to Conductive PEDOT Films: A Spectroelectrochemical Study

Santiago Rodríguez-Jiménez; Michael S Bennington; Alireza Akbarinejad; Elliot J Tay; Eddie Wai Chi Chan; Ziyao Wan; Abdullah M Abudayyeh; Paul Baek; Humphrey L C Feltham; David Barker; Keith C Gordon; Jadranka Travas-Sejdic; Sally Brooker

doi:10.1021/acsami.0c16317

Electroactive Metal Complexes Covalently Attached to Conductive PEDOT Films: A Spectroelectrochemical Study

ACS Appl Mater Interfaces. 2021 Jan 13;13(1):1301-1313. doi: 10.1021/acsami.0c16317. Epub 2020 Dec 22.

Authors

Santiago Rodríguez-Jiménez^{1

2}, Michael S Bennington^{1

2}, Alireza Akbarinejad^{2

3}, Elliot J Tay^{1

2}, Eddie Wai Chi Chan^{2

3}, Ziyao Wan^{2

3}, Abdullah M Abudayyeh^{1

2}, Paul Baek^{2

3}, Humphrey L C Feltham^{1

2}, David Barker^{2

3}, Keith C Gordon^{1

2}, Jadranka Travas-Sejdic^{2

3}, Sally Brooker^{1

2}

Affiliations

¹ Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
² The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand.
³ Polymer Biointerface Centre and School of Chemical Sciences, The University of Auckland, Auckland 1010, New Zealand.

PMID: 33351602
DOI: 10.1021/acsami.0c16317

Abstract

The successful covalent attachment, via copper(I)-catalyzed azide alkyne cycloaddition (CuAAC), of alkyne-functionalized nickel(II) and copper(II) macrocyclic complexes onto azide (N₃)-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films on ITO-coated glass electrodes is reported. To investigate the surface attachment of the selected metal complexes, which are analogues of the cobalt-based complex previously reported to be a molecular catalyst for hydrogen evolution, first, three different PEDOT films were formed by electropolymerization of pure PEDOT or pure N₃-PEDOT, and last, 1:2N₃-PEDOT:PEDOT were formed by co-polymerizing a 1:4 mixture of N₃-EDOT:EDOT monomers. The successful surface immobilization of the complexes on the latter two azide-functionalized films, by CuAAC, was confirmed by X-ray photoelectron spectroscopy (XPS) and electrochemistry as well as by UV-vis-NIR and resonance Raman spectroelectrochemistry. The ratio between the N₃ groups, and hence, the number of surface-attached metal complexes after CuAAC functionalization, in pristine N₃-PEDOT versus 1:2N₃-PEDOT:PEDOT is expected to be 3:1 and seen to be 2.86:1 with a calculated surface coverage of 3.28 ± 1.04 and 1.15 ± 0.09 nmol/cm², respectively. The conversion, to the metal complex attached films, was lower for the N₃-PEDOT films (Ni 74%, Cu 76%) than for the copolymer 1:2N₃-PEDOT:PEDOT films (Ni 83%, Cu 91%) due to the former being more sterically congested. The Raman and UV-vis-NIR results were simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively, and showed good agreement with the experimental data. Importantly, the spectroelectrochemical behavior of both anchored metal complexes is analogous to that of the free metal complexes in solution. This proves that PEDOT films are promising conducting scaffolds for the covalent immobilization of metal complexes, as the existing electrochromic features of the complexes are preserved on immobilization, which is important for applications in electrocatalytic proton and carbon dioxide reduction, optoelectronics, and sensing.

Keywords: X-ray photoelectron spectroscopy; covalent immobilization on PEDOT; density functional theory; spectroelectrochemistry; surface-bound metal complexes.