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Nitrogenated Polycyclic Aromatic Hydrocarbons (N-PAHs): Nanostructures, Functionalization and Electronic Properties (NanoFun)

Applicant Liu Shi-Xia
Number 204053
Funding scheme Project funding (Div. I-III)
Research institution Departement für Chemie, Biochemie und Pharmazie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Inorganic Chemistry
Start/End 01.10.2021 - 30.09.2025
Approved amount 566'018.00
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All Disciplines (2)

Discipline
Inorganic Chemistry
Microelectronics. Optoelectronics

Keywords (8)

tetraazapyrene ; electrochemistry and ultrafast spectroscopy; metal surface-assisted chemical reaction; nitrogenated polycyclic aromatic hydrocarbons; electron donor-acceptor ensembles; intramolecular charge transfer ; supramolecular coordination chemistry; molecular electronics

Lay Summary (German)

Lead
Die Titelverbindungen sind wegen ihren elektronischen Eigenschaften eine wichtige Verbindungsklasse. Eine präzise N-Dotierung ermöglicht, z. B. den Ladungstransport der nanoelektronischen Bausteine gezielt zu variieren. Mit den Methoden der Lösungschemie können nur beschränkt neue Moleküle hergestellt werden. Mit der hier angewendeten Synthese auf Metalloberflächen werden jedoch ausgedehnte Nanostrukturen möglich, wobei Einzelmoleküle zu atomar-dünnen Ketten, Bänder und Schichten verbunden werden.
Lay summary

Ziel des Projekts

Präparative Methoden basierend auf der «Chemie in Lösung» werden erprobt. Die elektronischen Eigenschaften der neuen Elektron-Donor – Elektron-Akzeptor Verbindungen werden mit elektrochemischen, optisch-spektroskopischen und theoretischen Methoden untersucht. Wichtig ist, dass auch komplementäre Synthesemethoden auf Metalloberflächen im Ultrahochvakuum erprobt werden, was zu neuen Nanostrukturen führt. Mit der Rastertunnelmikroskopie werden diese molekularen Strukturen mit atomarer Auflösung sichtbar gemacht und deren elektronischen Eigenschaften auf der Nanometer-Skala untersucht. 

Wissenschaftlicher und gesellschaftlicher Kontext des Projekts

Der multidisziplinäre Ansatz von Synthese, Nano-Physik, Laserspektroskopie und Theorie zeichnet das Projekt aus. Neben den potentiellen Implikationen für die molekulare Elektronik stellt dies für die Ausbildung aller involvierten Studierenden einen immensen Mehrwert dar und die kollaborative Forschung kann «in Praxis» geübt werden. 

Direct link to Lay Summary Last update: 26.09.2021

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Abstract

Our keen interest in nitrogenated polycyclic aromatic hydrocarbons (N-PAHs) stems from their intrinsic optoelectronic and electrochemical properties, high thermal and chemical stability, as well as their appealing charge and exciton transport characteristics. Electronic structures of N-PAHs, in regard to discrete HOMO-LUMO gaps, energy levels and the preferential transport of holes or electrons, are significantly affected by the number and the positions of embedded nitrogen atoms, and also the number of fused rings and their ordering in the aromatic framework. Consequently, all these factors provide an unique opportunity to develop a strategy for improving performance as organic semiconductors with tailor-made functions. In NanoFun, different synthetic methodologies to achieve stable N-PAHs will be explored. It is envisaged to develop novel materials with excellent charge carrier mobility, high stability and efficient fission by covalent linkage of various functional components including redox-active tetrathiafulvalene and azulene into the tetraazapyrene through the pyrazine/quinoxaline bridge(s). They can be prepared by solution-based methods using imine-type cyclocondensations. At the heart of this chemistry lies the Schiff-base formation reaction. Nevertheless, rigid and large N-PAHs often show a great tendency to aggregate, leading to extremely low solubility which largely impedes their synthesis and characterization. As a result, on-surface chemical synthesis can be implemented for the formation of pi-extended N-PAHs, such as one-dimensional (1D) and two-dimensional (2D) graphene nanoribbons (N-GNRs) or nanosheets that are unattainable by wet-chemistry. Importantly, this complementary synthesis enables to identify and visualize chemical structures of intermediates and products at the atomic-scale by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).The goal of this actual project consists in the attainment of a series of large p-extended electro-active N-PAHs, hence targeting material science via a judicious chemical design, either by wet-chemistry or on-surface chemical reactions. A vital issue concerns the N substitution effect, such as the N/C ratio and positions of N atoms, on optoelectronic properties of the resultant N-PAHs, which, however, remains an extremely complex subject. Overall, the proposed activities will allow us to tackle key challenges that definitely will give new momentum to the field of molecular organic electronics.
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