Edge Functionalization of Structurally Defined Graphene Nanoribbons for Modulating the Self-Assembled Structures

Abstract

Edge functionalization of bottom-up synthesized graphene nanoribbons (GNRs) with anthraquinone and naphthalene/perylene monoimide units has been achieved through a Suzuki coupling of polyphenylene precursors bearing bromo groups, prior to the intramolecular oxidative cyclo-dehydrogenation. High efficiency of the substitution has been validated by MALDI-TOF MS analysis of the functionalized precursors and FT-IR, Raman, and XPS analyses of the resulting GNRs. Moreover, AFM measurements demonstrated the modulation of the self-assembling behavior of the edge-functionalized GNRs, revealing that GNR-PMI formed an intriguing rectangular network. This result suggests the possibility of programming the supramolecular architecture of GNRs by tuning the functional units.

Multiwavelength Raman spectroscopy of ultranarrow nanoribbons made by solution-mediated bottom-up approach

“…at a similar frequency as for -C12 and -(Br,C12), possibly suggesting it having the same origin. Moreover, weaker peaks appear and they could be attributed to coupled modes [49], since AQ is known to display Raman modes in this energy region [30]. On the other hand, the acoustic region of the Raman spectra of -PMI and -NMI GNRs are similar and a clear, distinct peak attributable to a RLBM cannot be identified.…”

“…4-cGNR-Br was then prepared by adapting the synthetic method of GNR-C12, using a bromo-functionalized monomer precursor [61]. The dye-functionalized GNRs, i.e., 4-cGNR-PMI, -NMI and -AQ, were synthesized by adapting the pre-functionalization protocol previously reported for hexa-peri-hexabenzocoronene derivatives [30]. Finally, 9/15-aGNRs were synthesized as described in Refs.…”

“…We have up to now discussed the Raman spectra taken at fixed wavelength, we now move to the multiwavelength analysis, as many features of the Raman spectrum of GNRs strongly change with the excitation energy, as discussed in the Background section. In particular, we explore excitation energies ranging from 1.57 to 2.71 eV, i.e., pre-resonant and resonant conditions considering the optical gap of these GNRs [30]. We here focus on the excitation energy dependence of both D and G peak for all the studied GNRs.…”

“…While further studies would be needed to clarify this point, we note that in these cases the Br is replaced with chains and dyes. Both Br and the chosen dyes have an electron-withdrawing character, and the dyes present electronic states close to the GNR gap and vibrational states in the same energy region: all of this can impact the intrinsic electronic and optical properties of the ribbon itself [30,76,77] and influence the coupling with vibrations in resonant regime. Moreover, the random functionalization pattern can induce localization of the electronic states further influencing the coupling with the vibrations.…”

Regioselective Bromination and Functionalization of Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene with Zigzag Edges

“…[2] Numerous nanographenes with armchair edge structures have been synthesized and reported, showingt unable energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital( LUMO), mainly dependento nt he shapes and sizes of their aromatic cores. [3] Edge functionalization of nanographenesh as been widely studied,i mparting them with intriguing properties, [4] such as n-types emiconductor characteristics, [5] intramolecular charge-transfer, [6] and/or liquid-crystalline nature, [7] distinct from their pristine, non-substituted counterparts.H owever,s uch functionalization predominantly relies on the modificationo fs tarting materials and/orp recursor structures involving multiple synthetic steps, while post-synthetic direct substitution of nanographenee dges has been starkly underexplored. In particular,w hile there are severalv ersatile methods, such as direct borylation [8] or perchlorination of the nanographene edges, [9] selectivee dge-halogenation has rarely been reported, [10] despite the fact that halogeng roups can be converted into various other functional groups through transition-metal-catalyzed couplingr eactions.…”