Effect of Edge Functionalization on the Bottom‐Up Synthesis of Nano‐Graphenes

Abstract

We demonstrate the effect of edge functionalization on the on‐surface Ullmann coupling of nano‐carbon materials. Unlike 10,10′‐Dibromo‐9,9′‐bianthryl (DBBA), which is widely known to form anthracene polymers and armchair‐edge graphene nanoribbons on Au(111), newly‐developed precursor named 5‐bromo‐11(10‐bromoanthracene‐9‐yl)anthra[2,3‐b : 7,6‐b′]dithiophene (BABAT) with isomers, which has similar structure as DBBA with one anthracene substituted with anthradithiophene, was found to make intramolecular C−C bonding instead of long anthracene polymers after annealing at 200 °C on Au(111). The mechanism was investigated using first‐principle density functional theory, which revealed that on‐surface polymerization is not kinetically preferred in case of BABAT. The reaction rate of intramolecular C−C bonding of BABAT is ∼206 times faster than that of DBBA. The intramolecular C−C bonding in DBBA biradicals, on the other hand, do not take place because of faster reverse reaction. By referring to electron density of BABAT biradicals, it was concluded that thiophene functionalization modifies distribution of electron density in BABAT radicals and facilitates electrophilic addition, leading to intramolecular C−C bonding after 200 °C annealing. These results indicate that the design of radical moiety is particularly important in the on‐surface Ullmann‐type coupling.

Introducing Design Strategies to Preserve N‐Heterocycles Throughout the On‐Surface Synthesis of Graphene Nanostructures

“…Adding nitrogen atoms to the edges and pores of graphene-based nanostructures is an effective strategy to provide a manifold of interesting properties that amplify the potential applications of several heteroatoms and functional groups have been introduced with the same atomic precision as the rest of the structural parameters. [2,[23][24][25][26][27][28][29][30][31][32][33] However, these studies also reflect that, in particular when located at the edges, the functional groups in most cases suffer from isomerization, [33] chemical transformation, [25] or partial [30,31] and even total cleavage [34] during the thermally assisted on-surface synthesis.…”

“…[ 22 ] The best example is the bottom‐up synthesis of graphene nanoribbons (GNRs), where several heteroatoms and functional groups have been introduced with the same atomic precision as the rest of the structural parameters. [ 2,23–33 ] However, these studies also reflect that, in particular when located at the edges, the functional groups in most cases suffer from isomerization, [ 33 ] chemical transformation, [ 25 ] or partial [ 30,31 ] and even total cleavage [ 34 ] during the thermally assisted on‐surface synthesis.…”

On-surface synthesis of hydroxy-functionalized graphene nanoribbons through deprotection of methylenedioxy groups

“…27 Consequently, a limited number of reports have been made on the edge-functionalized GNRs so far, 28-30 while some failures have been reported as well. 31 In this research, we report on the bottom-up growth of GNRs with edges functionalized by hydroxy functional groups. To realize the synthesis of edge-hydroxylated GNRs, catechol units in the GNR precursor were protected by methylene acetal.…”

“…27 Consequently, a limited number of reports have been made on edge-functionalized GNRs so far, 28–30 while some failures have been reported as well. 31…”

“…27 Consequently, a limited number of reports have been made on edge-functionalized GNRs so far, [28][29][30] while some failures have been reported as well. 31 In this research study, we report on the bottom-up growth of GNRs with edges functionalized by hydroxy functional groups.…”