Synthesis of N = 8 Armchair Graphene Nanoribbons from Four Distinct Polydiacetylenes

Abstract

We demonstrate a highly efficient thermal conversion of four differently substituted polydiacetylenes (PDAs 1 and 2a-c) into virtually indistinguishable N = 8 armchair graphene nanoribbons ([8]GNR). PDAs 1 and 2a-c are themselves easily accessed through photochemically initiated topochemical polymerization of diynes 3 and 4a-c in the crystal. The clean, quantitative transformation of PDAs 1 and 2a-c into [8]GNR occurs via a series of Hopf pericyclic reactions, followed by aromatization reactions of the annulated polycyclic aromatic intermediates, as well as homolytic bond fragmentation of the edge functional groups upon heating up to 600 °C under an inert atmosphere. We characterize the different steps of both processes using complementary spectroscopic techniques (CP/MAS C NMR, Raman, FT-IR, and XPS) and high-resolution transmission electron microscopy (HRTEM). This novel approach to GNRs exploits the power of crystal engineering and solid-state reactions by targeting very large organic structures through programmed chemical transformations. It also affords the first reported [8]GNR, which can now be synthesized on a large scale via two operationally simple and discrete solid-state processes.

Polycyclic aromatic hydrocarbons in the graphene era

“…The band gap in each group decreases as the ribbon width increases, whereas in different groups but with the same n, the band gap is dependent on the group (3n +2≪3n<3n+1) that the GNRs belong to (Figure 20(c)) [22,160]. In recent years, AGNRs with different widths have been precisely synthesized via the bottom-up procedure [126,140,[142][143][144][145][146]149,[161][162][163][164][165][166][167][168][169][170], establishing the widthdependent band gaps as determined by theory [22,171]. ZGNRs are predicted to have localized edge states that can be spin-polarized, showing great potential for spintronic applications [160,172].…”

“…To achieve atomic precision, Tan, Feng and Müllen et al [43] developed an efficient edge chlorination protocol for nanographene molecules with an excess amount of iodine monochloride and a catalytic amount of aluminum chloride ( Figure 32). Chlorinated nanographene molecules (157)(158)(159)(160)(161)(162) exhibit enhanced solubility in common organic solvents; thus, the single-crystal growth of such large PAHs is possi-ble. Not only the detailed bond lengths of the graphenic structures but also the contorted geometries induced by the steric hindrance between chlorines have been unambiguously elucidated.…”

Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

“…Using av ery similar strategy,t he same group reported the synthesis of the largest armchair GNR of the 3p + 2f amily known to date,namely a[8] A GNRs 8a-c (Scheme 1). [55] This type of GNRs is particularly interesting as it is expected to exhibit am uch lower band gap value than the 3p and 3p + 1f amily. [56] Raman and IR spectroscopy as well as CP/MAS 13 CNMR analysis comply with the targeted structure.H owever,t he harsh thermal treatment needed to perform the cyclization (Hopf reaction) results in the loss of the solubilizing side chains,m aking solution-phase analysis and solution processing impracticable.…”

On‐Surface Synthesis of 8‐ and 10‐Armchair Graphene Nanoribbons

“…As for on‐surface synthesis of AGNRs, 4, 6, 8, and 10‐AGNRs have not yet prepared through molecular precursors, but among them, 6‐ and 10‐AGNRs have been obtained via lateral self‐fusing of poly‐ para ‐phenylene and 5‐AGNRs on Au (111), respectively . Apart from one report of 8‐AGNRs via a solid‐state topochemical polymerization, on‐surface synthesis of 8‐AGNRs has not yet been achieved due to the lack of both precursor molecules and 4‐AGNRs for self‐fusing, making it a critically missing case in the whole AGNRs family. While the subfamilies of N‐AGNRs are classified as N = 3 p + 2, 3 p + 1, and 3 p of carbon numbers across the width ( N , p are positive integers), poly‐ para ‐phenylene is, therefore, the minimum repeating ribbon and can be served as a ladder ribbon for the widening of AGNRs.…”