Electrodeposition of PAH-Dendrimers via Electrochemical Oxidation an Integrated Experimental-Theoretical Approach
Authors: Bonechi Marco , Giurlani Walter , Marchetti Andrea , Campidelli Stephane , Kowalik Remigiusz , Fontanesi Claudio , Innocenti Massimo 
Published: December 2024

Polycyclic Aromatic Hydrocarbons (PAH) are sizeable molecules formally obtained by the multiple “fusion” of aromatic rings. Such nanometre-size carbon materials show extremely interesting physical properties: electrical conductivity, light absorption, and emission, leading to their use in organic electronics, sensors, and energy applications [1].

Different experimental strategies can be exploited to form larger molecular architectures starting from non-conjugated systems. Classical approaches are mostly based on chemical synthetic procedures that involve the use of polynuclear aromatic hydrocarbons (PAH). More recently many works have shown the advantages of new electrochemical PAH synthesis via an anodic electrochemical oligomerization [2]. Electric current can be used as an oxidant to replace strong chemical oxidizing agents for new C–C bond generation [3] obtaining PAH film with Charge and Exciton Transport on the electrode surface [4].

For this study, the C96 dendrimers (PPD) was synthesized by the Diels-Alder reaction between the 1,3,5-triethynylbenzene and the 2,3,4,5-tetra phenyl-2,4-cyclopentadien-1-one according to literature procedure [5]. Thus, pPPD film structures were electrochemically grown on ultra-flat indium tin oxide (ITO) electrodes by electrochemical oxidation of C96 PPD dendrimers. A preliminary characterization of the relevant films was carried out using Laser Desorption-Ionization Mass Spectra (MALDI-TOF-MS), Gel-Permeation Chromatography (GPC) measurements, and UV/vis spectroscopy. In particular, the electronic properties of pPPD were studied using near edge XAS determining the valence band photoemission. The experimental results were then compared with DFT calculations, to assess the extent of conjugation obtained in the materials. All the collected experimental evidence consistently indicates that uniform films of pPDD supramolecular architectures are formed via electrochemical oxidation. Remarkably, the use of electrochemical-based methods paves the way for preparing and characterizing complex molecular architectures, from 2D SAMs to organic, inorganic, and hybrid polymers.

The authors acknowledge the support offered by Project 2022NW4P2T CUP B53D23013890006 “From metal nanoparticles to molecular complexes in electrocatalysis for green hydrogen evolution and simultaneous fine chemicals production” PRIN2022 Progetti di Ricerca di Rilevante Interesse Nazionale funded by the Italian Ministry of University and Research and NextGenerationEU.

References

[1] Z. Liu, S. Fu, X. Liu, A. Narita, P. Samorì, M. Bonn, H.I. Wang, Small Size, Big Impact: Recent Progress in Bottom‐Up Synthesized Nanographenes for Optoelectronic and Energy Applications, Advanced Science 9 (2022) 2106055. https://doi.org/10.1002/advs.202106055.

[2] C. Zeng, W. Zheng, H. Xu, S. Osella, W. Ma, H.I. Wang, Z. Qiu, K. Otake, W. Ren, H. Cheng, K. Müllen, M. Bonn, C. Gu, Y. Ma, Electrochemical Deposition of a Single‐Crystalline Nanorod Polycyclic Aromatic Hydrocarbon Film with Efficient Charge and Exciton Transport, Angew Chem Int Ed 61 (2022). https://doi.org/10.1002/anie.202115389.

[3] M. Bonechi, W. Giurlani, A. Stefani, A. Marchetti, M. Innocenti, C. Fontanesi, Resorcinol electropolymerization process obtained via electrochemical oxidation, Electrochim. Acta 428 (2022) 140928. https://doi.org/10.1016/j.electacta.2022.140928.

[4] M. Bonechi, A. Marchetti, W. Giurlani, D. Vanossi, L. Pasquali, S. Campidelli, C. Fontanesi, M. Innocenti, Electrochemical growth of PAH-dendrimers supramolecular films. An integrated experimental-theoretical approach, Electrochimica Acta 474 (2024) 143435. https://doi.org/10.1016/j.electacta.2023.143435.

[5] V.S. Iyer, M. Wehmeier, J.D. Brand, M.A. Keegstra, K. Müllen, From Hexa‐ peri ‐hexabenzocoronene to “Superacenes,” Angew. Chem. Int. Ed. Engl. 36 (1997) 1604–1607. https://doi.org/10.1002/anie.199716041.