Porphyrin-Graphene Nanoribbon (PGNR) Conjugates: Solution Syntheses and Properties
Synthesis and Properties of Functional Materials
Final Report Abstract
Molecular wires are promising components for nanoelectronics to boost the efficiency of future electronic devices, while decreasing device sizes and energy consumption. Graphene nanoribbons (GNRs) are emerging as molecular wires with exceptional electronic properties and their conjugation with (metal)porphyrins has been regarded as a promising strategy to fine-tune these properties. Nevertheless, by now, atomically precise synthesis of porphyrin-fused graphene nanoribbon (PGNR) has not been achieved yet, which impedes the exploration of their structure-property relationships. In this project, we targeted on the design and bottom-up synthesis of PGNRs using stepwise solution reactions. In our first study, we successfully synthesized a series of fully edge-fused porphyrin-anthracene oligomeric ribbons. They were prepared via oxidative cyclodehydrogenation of singly linked porphyrin-anthracene precursors. The extended π-conjugation system causes dramatic red-shift of their absorption spectra and decrease of energy gaps. As a proof of concept, the coordination metal in the fused dimer was then changed from Ni to Mg, using p-tolylmagnesium bromide, providing access to free-base and Zn complexes. However, we could not extend the length of the nanoribbons to longer than three repeating units, mainly suffering from decreased solubility of longer molecules. In our second study, we changed the design and successfully synthesized the long-awaited PGNR in solution. Our synthesis was based on Yamamoto polymerization of a rationally designed porphyrin monomer containing two chlorinated benzo[m]tetraphenes, followed by cyclodehydrogenation. The high yield of the cyclodehydrogenation reaction was verified by the synthesis and unambiguous characterization of model compounds containing 1–3 porphyrin units with lengths of up to 6 nm. By using a combination of solid-state NMR, UV-vis-NIR absorption, IR, Raman and X-ray photoelectron spectroscopy, the structure of the final PGNR were unambiguously characterized. An optical bandgap of 1.0 eV was calculated from the onset of absorption spectrum, which represents one of the narrowest bandgaps for solution-synthesized GNRs. This PGNR provides an opportunity to investigate charge transport within the backbone and test the effect of incorporating porphyrin units. To this end, by using a contact-free ultrafast optical pump–terahertz probe spectroscopy, a high local charge mobility of 450 cm2 V^–1 s^–1 was measured. In single-molecular field-effect transistors using graphene-based electrodes, the first prototypical devices show mobilities up to 40 cm2 V^–1 s^–1. These results highlight the potential application of PGNRs for single-molecular electronic devices. Our results contribute to a deeper understanding of porphyrin-based molecular wires and how they perform in single molecular electronic devices.
Publications
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Jul. 2022, The 19th International Symposium on Novel Aromatic Compounds (ISNA-19), Warsaw, Poland: β,β-Linked Cyclic Porphyrin Oligomers as Receptors for Fullerenes
Qiang Chen
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Anthracene‐Porphyrin Nanoribbons. Angewandte Chemie International Edition, 62(31).
Zhu, He; Chen, Qiang; Rončević, Igor; Christensen, Kirsten E. & Anderson, Harry L.
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Porphyrin-Fused Graphene Nanoribbons. American Chemical Society (ACS).
Chen, Qiang; Lodi, Alessandro; Zhang, Heng; Gee, Alex; Wang, Hai; Kong, Fanmiao; Clarke, Michael; Edmondson, Matthew; Hart, Jack; O.’Shea, James; Stawski, Wojciech; Baugh, Jonathan; Narita, Akimitsu; Saywell, Alex; Bonn, Mischa; Müllen, Klaus; Bogani, Lapo & Anderson, Harry
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β,β-Directly Linked Porphyrin Rings: Synthesis, Photophysical Properties, and Fullerene Binding. Journal of the American Chemical Society.
Chen, Qiang; Thompson, Amber L.; Christensen, Kirsten E.; Horton, Peter N.; Coles, Simon J. & Anderson, Harry L.
