An official website of the United States government
Abstract This work provides a detailed multi‐component analysis of aromaticity in monosubstituted (X = CH3, C, C, NH2, NH−, NH+, OH, O−, and O+) andpara‐homodisubstituted (X = CH3, CH2, NH2, NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single‐reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELFπ), electronic (MCI), magnetic (NICS), and stability (S0–T1splitting) properties. The findings reveal that appropriateπ‐electron‐donating andπ‐electron‐accepting substituents with suitable size and symmetry can interact with theπ‐system of the ring, significantly influencingπ‐electron delocalization. While the charge factor has a minimal impact onπ‐electron delocalization, the presence of apzorbital capable of interacting with theπ‐electron delocalization is the primary factor leading to a deviation from the typical aromaticity characteristics observed in benzene.
more »
« less
Stepwise Generation of Mono‐, Di‐, and Triply‐Reduced Warped Nanographenes: Charge‐Dependent Aromaticity, Surface Nonequivalence, Swing Distortion, and Metal Binding Sites
Abstract The stepwise chemical reduction of a molecular warped nanographene (WNG) having a negatively curved π‐surface and defined C80H30composition with Cs metal used as the reducing and complexing agent allowed the isolation of three different reduced states with one, two, and three electrons added to itsπ‐conjugated system. This provided a unique series of nanosized carbanions with increasing negative charge for in‐depth structural analysis of consequences of controlled electron charging of non‐planar nanographenes, using X‐ray crystallographic and computational tools. The 3D molecular electrostatic potential (MEP) maps identified the negative charge localization at the central part of the WNG surface where selective coordination of Cs+ions is confirmed crystallographically. In‐depth theoretical investigation revealed a complex response of the WNG to the stepwise electron acquisition. The extended and contorted π‐surface of the WNG undergoes subtle swinging distortions that are accompanied by notable changes in the electronic structure and site‐dependent aromaticity of the resulting carbanions.
more »
« less
- Award ID(s):
- 2003411
- PAR ID:
- 10307809
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 48
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 25445-25453
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F6TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F6TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm2V−1s1being estimated from SCLC measurements for BTBT:F6TNAP and CBZ:F6TNAP cocrystals.more » « less
-
Abstract Incorporation of a five‐membered ring into a helicene framework disrupts aromatic conjugation and provides a site for selective deprotonation. The deprotonation creates an anionic cyclopentadienyl unit, switches on conjugation, leads to a >200 nm red‐shift in the absorbance spectrum and injects a charge into a helical conjugated π‐system without injecting a spin. Structural consequences of deprotonation were revealed via analysis of a monoanionic helicene co‐crystallized with {K+(18‐crown‐6)(THF)} and {Cs+2(18‐crown‐6)3}. UV/Vis‐monitoring of these systems shows a time‐dependent formation of mono‐ and dianionic species, and the latter was isolated and crystallographically characterized. The ability of the twisted helicene frame to delocalize the negative charge was probed as a perturbation of aromaticity using NICS scans. Relief of strain, avoidance of antiaromaticity, and increase in charge delocalization assist in the additional dehydrogenative ring closures that yield a new planarized decacyclic dianion.more » « less
-
Abstract Mono‐ and dianions of 2‐tert‐butyl‐3a2‐azapentabenzo[bc,ef,hi,kl,no]corannulene (1 a) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na+(18‐crown‐6)(THF)2}3{Na+(18‐crown‐6)(THF)}(1 a2−)2], revealed the presence of a naked dianion. In contrast, controlled reaction of1 awith Cs allowed the isolation of singly and doubly reduced forms of1 a, both forming π‐complexes with cesium ions in the solid state. In [{Cs+(18‐crown‐6)}(1 a−)]⋅THF, asymmetric binding of the Cs+ion to the concave surface of1 a−is observed, whereas in [{Cs+(18‐crown‐6)}2(1 a2−)], two Cs+ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.more » « less
-
Abstract Two‐dimensional graphitic metal–organic frameworks (GMOF) often display impressive electrical conductivity chiefly due to efficient through‐bond in‐plane charge transport, however, less efficient out‐of‐plane conduction across the stacked layers creates large disparity between two orthogonal conduction pathways and dampens their bulk conductivity. To address this issue and engineer higher bulk conductivity in 2D GMOFs, we have constructed via an elegant bottom‐up method the first π‐intercalated GMOF (iGMOF1) featuring built‐in alternate π‐donor/acceptor (π‐D/A) stacks of CuII‐coordinated electron‐rich hexaaminotriphenylene (HATP) ligands and non‐coordinatively intercalated π‐acidic hexacyano‐triphenylene (HCTP) molecules, which facilitated out‐of‐plane charge transport while the hexagonal Cu3(HATP)2scaffold maintained in‐plane conduction. As a result, iGMOF1 attained an order of magnitude higher bulk electrical conductivity and much smaller activation energy than Cu3(HATP)2(σ=25 vs. 2 S m−1,Ea=36 vs. 65 meV), demostrating that simultaneous in‐plane (through‐bond) and out‐of‐plane (through πD/A stacks) charge transport can generate higher electrical conductivity in novel iGMOFs.more » « less
