Fusing a Planar Group to a π‐Bowl: Electronic and Molecular Structure, Aromaticity and Solid‐State Packing of Naphthocorannulene and its Anions

Abstract

Molecular and electronic structure, reduction electron transfer and coordination abilities of a polycyclic aromatic hydrocarbon (PAH) having a planar naphtho-group fused to the corannulene bowl have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison of naphtho[2,3-a]corannulene (C H , 1) with parent corannulene (C H , 2) revealed the effect of framework topology change on electronic properties and aromaticity of 1. The presence of two reduction steps for 1 was predicted theoretically and confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at -2.30 and -2.77 V versus Fc were detected by cyclic voltammetry (CV) measurements, demonstrating accessibility of the corresponding mono- and dianionic states of 1. The products of the singly and doubly reduced napththocorannulene were prepared using chemical reduction with Group 1 metals and isolated as sodium and rubidium salts. Their X-ray diffraction study revealed the formation of "naked" mono- and dianions crystallized as solvent-separated ion products with one or two sodium cations as [Na (18-crown-6)(THF) ][C H ] and [Na (18-crown-6)(THF) ] [C H ] (3⋅THF and 4⋅THF, respectively). The dianion of 1 was also isolated as a contact-ion complex with two rubidium countercations, [{Rb (18-crown-6)} (C H )] (5⋅THF). The structural consequences of adding one and two electrons to the carbon framework of 1 are compared for 3, 4 and 5. Changes in aromaticity and charge distribution stemming from the stepwise electron acquisition are discussed based on DFT computational study.

Stack the Bowls: Tailoring the Electronic Structure of Corannulene‐Integrated Crystalline Materials

“…The unique curvature of π‐bowls (πBs) distinguishes them from more traditional flat polycyclic aromatic hydrocarbons (PAHs) and, in combination with an unusual electronic structure, results in a number of intriguing properties including, but not limited to, surface charge stabilization, high reversible lithium capacity, bowl‐to‐bowl inversion, a significant dipole moment, and high charge mobility . This combination of material properties can open a pathway for πB utilization in applications ranging from optoelectronic devices or electrodes to thermoresponsive materials …”

“…However, several challenges still had to be addressed for not only reaction condition development but also synthesis of corannulene‐based building blocks on a gram scale. The latter challenge has been overcome owing to recent advances in πB chemistry, allowing for the preparation of azide‐containing corannulene (πB‐C 20 H 9 N 3 , Figure , Scheme S5) using a 12‐step procedure as well as pristine corannulene (πB‐C 20 H 10 ) by a 9‐step approach (Scheme S5) …”

Stack the Bowls: Tailoring the Electronic Structure of Corannulene‐Integrated Crystalline Materials

“…The unique curvature of p-bowls (pBs) distinguishes them from more traditional flat polycyclic aromatic hydrocarbons (PAHs) and, in combination with an unusual electronic structure,results in anumber of intriguing properties including, but not limited to,s urface charge stabilization, high reversible lithium capacity,b owl-to-bowl inversion, as ignificant dipole moment, and high charge mobility. [1][2][3][4][5][6][7][8] This combination of material properties can open ap athway for pBu tilization in applications ranging from optoelectronic devices or electrodes to thermoresponsive materials. [4,9,10] Herein, we demonstrated, for the first time,h ow pB integration (in particular,c orannulene [pB-C 20 H 10 ]) inside insulating porous scaffolds could tune electronic properties resulting in circa 10 000-fold conductivity enhancement.…”

“…[22] Both selected frameworks,p ossessing layered structures with ap ore aperture of 33 ,m aintain structural integrity under aw ide pH range [22] making it possible to explore anumber of synthetic conditions for pBi mmobilization without material degradation. However,several challenges still had to be addressed for not only reaction condition development but also synthesis of corannulene-based building blocks on ag ram scale.T he latter challenge has been overcome owing to recent advances in pB chemistry, [3,[23][24][25][26] allowing for the preparation of azide-containing corannulene (pB-C 20 H 9 N 3 , Figure 1, Scheme S5) using a1 2-step procedure [26] as well as pristine corannulene (pB-C 20 H 10 )b ya9-step approach (Scheme S5). [25] As tepwise approach was devised for the investigation of reaction conditions for ac opper-catalyzed azide-alkyne cycloaddition (CuAAC), which involved the development of synthetic methods using less bulky and more affordable moieties (for example,2 -azidoethanol, Figure 1) before pursuing the reaction with the labor-demanding pB-C 20 H 9 N 3 .T herefore,w es tarted with molecular building blocks,such as 2-azidoethanol and BPTA, to observe reaction progress using solution NMR spectroscopy,incontrast to the insoluble COFs (Supporting Information, Figures S18-S20).…”

Flat corannulene: when a transition state becomes a stable molecule

“…16,17 Expectedly, increased bowl depths 18,19 and higher inversion barriers 20,21 were reported for derivatives in which two peri-positions were annulated to become part of an additional 5-or 6-membered ring. [22][23][24][25] However, computations and experiments have shown that changing the aromatic system's electronic properties by either ring annelation [26][27][28][29][30] or benzannulation [30][31][32][33] on the rim reduces the bowl depth ( Fig. 1).…”