Bottom-Up Synthesis of Soluble and Narrow Graphene Nanoribbons Using Alkyne Benzannulations

Since the discovery of graphene, there is an increasing amount of research devoted to graphene materials, namely, graphene nanoribbons (GNRs). The "top-down" production of narrow (<10 nm wide), unoxidized, and easily processable GNRs with atomically precise edges is challenging, and therefore, new methods need to be developed. We have designed a "bottom-up" approach for the synthesis of very narrow (ca. 0.5 nm) and soluble GNRs using a nonoxidative alkyne benzannulation strategy promoted by Brønsted acid. Suzuki polymerization was used to produce the GNR precursor, a poly(2,6-dialkynyl-p-phenylene) (PDAPP), with a weight-average molecular weight of 37.6 kg mol-1. Cyclization of the ethynylaryl side chains on PDAPP was efficiently achieved using Brønsted acids to ultimately produce the GNRs. Infrared and Raman spectroscopic characterization of the GNRs matches very well with calculated results. The formation of the GNRs was also supported by transmission electron microscopy (TEM) and scanning tunneling microscopy (STM).