Synthesis of Polybenzoquinolines as Precursors for Nitrogen‐Doped Graphene Nanoribbons

Abstract

Graphene nanoribbons (GNRs) represent promising materials for the next generation of nanoscale electronics. However, despite substantial progress towards the bottom-up synthesis of chemically and structurally well-defined all-carbon GNRs, strategies for the preparation of their nitrogen-doped analogs remain at a nascent stage. This scarce literature precedent is surprising given the established use of substitutional doping for tuning the properties of electronic materials. Herein, we report the synthesis of a previously unknown class of polybenzoquinoline-based materials, which have potential as GNR precursors. Our scalable and facile approach employs few synthetic steps, inexpensive commercial starting materials, and straightforward reaction conditions. Moreover, due to the importance of quinoline derivatives for a variety of applications, the reported findings may hold implications across a diverse range of chemical and physical disciplines.

Synthesis of Nitrogen‐Containing Rubicene and Tetrabenzopentacene Derivatives

“…[51,52] [d] The values were determined from the density functionalt heory calculations. Diels-Alder (Povarov) reaction, [38,39] the Heck coupling, [40,41] and base-mediated cyclodehydrohalogenation, [42,43] making it potentially useful for ab road range of researchers.T hird, given the difficulties inherent to designing n-type and ambipolar organic semiconductors [53,54] and the known utility of nitrogen substitution for coaxing such behavior from acenes, [32,33] the reported rubicenes and tetrabenzopentacenes hold particular promise as organic electronic functional materials.F inally,n itrogen-containing fullerenes and graphene nanoribbons remain relatively rare and challenging to prepare, [19][20][21][22][23][24][25] and as such, we envision that our approach could eventually prove valuable for the design and construction of extended doped carbonaceous frameworks.A ltogether, our findings may open new research avenues and provide unique opportunities for the solution-phase synthesis of novel carbon-based materials.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18] However,asmaller number of studies have reported the solutionphase synthesis of analogous nitrogen-doped constructs. [19][20][21][22][23][24][25][26][27] Indeed, the rational incorporation of nitrogen heteroatoms, while frequently challenging,i sk nown to be valuable for tuning the properties of graphitic systems, [28][29][30][31] as demonstrated by the successful molecular engineering of various Nheteroacenes for improved transistor performance. [32,33] Consequently,t he development of new routes to nitrogencontaining acenes,f ullerenes,a nd GNRs remains important for the next generation of semiconductor devices and technologies.…”

“…We began our studies by synthesizing rubicene 3 and tetrabenzopentacene 5 via the Povarov reaction, [38,39] as illustrated in Scheme 1a.T op repare compounds 3 and 5, we first formed bis(aldimine) 1 through ak nown literature procedure. [22,47,48] Subsequently,w eo btained 2 by reacting 1 with phenylacetylene in the presence of BF 3 ·OEt 2 as aLewis acid mediator and chloranil as an oxidant. [22,47,48] Similarly,we obtained 4 by reacting 1 with 1-ethynylnaphthalene in the presence of FeCl 3 as aLewis acid and aTEMPO oxonium salt as an oxidant (the alternative milder conditions improved the stability of the ethynyl precursor,i ncreasing the yield).…”

“…[22,47,48] Subsequently,w eo btained 2 by reacting 1 with phenylacetylene in the presence of BF 3 ·OEt 2 as aLewis acid mediator and chloranil as an oxidant. [22,47,48] Similarly,we obtained 4 by reacting 1 with 1-ethynylnaphthalene in the presence of FeCl 3 as aLewis acid and aTEMPO oxonium salt as an oxidant (the alternative milder conditions improved the stability of the ethynyl precursor,i ncreasing the yield). [49] Next, we synthesized 3 by using the palladium-catalyzed Heck coupling reaction [40,41] to form intramolecular CÀC bonds between the acene core and pendant phenyls of 2.I n aparallel approach, we synthesized 5 by using base-mediated cyclodehydrohalogenation [42,43] to form intramolecular CÀC bonds between the acene core and pendant napthyls of 4.…”

“…We then formed aldimine 7 and reacted it with 6, again in the presence of aLewis acid mediator and an oxidant, producing intermediate 8. [22,47,48] Next, we obtained 9 and 10, with 8 serving as the sole starting material. Thus,weprepared 9 by using the palladium-catalyzed Heck coupling reaction [40,41] to form intramolecular CÀCb onds between the acene core and pendant quinolines of 8.I naparallel approach, we prepared 10 by using base-mediated cyclodehydrohalogenation [42,43] to form intramolecular C À Cbonds between the acene core and pendant quinolines of 8.T hese pathways furnished desired products 9 and 10 in modest yields.…”