“…The bimodal D band and the significantly broadened 2D band in G4 (as compared with the N = 9 aGNR prepared previously 28 ) suggested stronger aggregation via a π–π stacking interaction, probably owing to the alkyl chains unsymmetrically placed on one side edge (vide infra) 37 . A weak but sharp peak at 870 cm −1 was observed for G5 , which is attributed to the N–S bond vibrations in the benzothiadiazole moiety 38 , 39 . Fig.…”
Despite the great promise of armchair graphene nanoribbons (aGNRs) as high-performance semiconductors, practical band-gap engineering of aGNRs remains an unmet challenge. Given that width and edge structures are the two key factors for modulating band-gaps of aGNRs, a reliable synthetic method that allows control of both factors would be highly desirable. Here we report a simple modular strategy for efficient preparation of N = 6 aGNR, the narrowest member in the N = 3p (p: natural number) aGNR family, and two unsymmetrically edge-functionalized GNRs that contain benzothiadiazole and benzotriazole moieties. The trend of band-gap transitions among these GNRs parallels those in donor–acceptor alternating conjugated polymers. In addition, post-functionalization of the unsymmetrical heterocyclic edge via C–H borylation permits further band-gap tuning. Therefore, this method opens the door for convenient band-gap engineering of aGNRs through modifying the heteroarenes on the edge.
“…The bimodal D band and the significantly broadened 2D band in G4 (as compared with the N = 9 aGNR prepared previously 28 ) suggested stronger aggregation via a π–π stacking interaction, probably owing to the alkyl chains unsymmetrically placed on one side edge (vide infra) 37 . A weak but sharp peak at 870 cm −1 was observed for G5 , which is attributed to the N–S bond vibrations in the benzothiadiazole moiety 38 , 39 . Fig.…”
Despite the great promise of armchair graphene nanoribbons (aGNRs) as high-performance semiconductors, practical band-gap engineering of aGNRs remains an unmet challenge. Given that width and edge structures are the two key factors for modulating band-gaps of aGNRs, a reliable synthetic method that allows control of both factors would be highly desirable. Here we report a simple modular strategy for efficient preparation of N = 6 aGNR, the narrowest member in the N = 3p (p: natural number) aGNR family, and two unsymmetrically edge-functionalized GNRs that contain benzothiadiazole and benzotriazole moieties. The trend of band-gap transitions among these GNRs parallels those in donor–acceptor alternating conjugated polymers. In addition, post-functionalization of the unsymmetrical heterocyclic edge via C–H borylation permits further band-gap tuning. Therefore, this method opens the door for convenient band-gap engineering of aGNRs through modifying the heteroarenes on the edge.
“…The difference observed now for the E–S stretching modes of anions [ 4 -SPh] − and [ 1 -SPh] − (E = Se, Te, respectively) reflects the prominent difference in the energies of the corresponding bonds E–S (see below) and therefore in their force constants. Thus, chalcogens in the anions under discussion do not behave as pseudoisotopes of each other as they do in some other cases of isostructural and isoelectronic chalcogen derivatives, making possible the empirical assignment of molecular vibrations they are involved in …”
New
products of coordination of anions X– (X
= F, I, PhS) to the Te atom of 3,4-dicyano-1,2,5-telluradiazole (1) were synthesized in high yields and characterized by X-ray
diffraction (XRD) as the salts [(Me2N)3S]+[1-F]− (9), [K(18-crown-6)]+[1-I]− (10), and
[K(18-crown-6)]+[1-SPh]−
·THF (11), respectively. In the crystal
lattice of 10, I atoms are bridging between two Te atoms.
The bonding situation in anions of the salts 9–11 and some other adducts of 1,2,5-chalcogenadiazoles (chalcogen
= S, Se, Te) and anions X– (X = F, Cl, Br, I, PhS)
was studied using DFT, QTAIM, and NBO calculations, for 9–11 in combination with UV–vis, IR/Raman,
and MS-ESI techniques. In all cases, the nature of the coordinate
bond is negative hyperconjugation involving the transfer of electron
density from X– to the heterocycles. The energy
of the bonding interaction varies in a range from ∼30 kcal
mol–1 comparable with energies of weak chemical
bonds (e.g., internal N–N bond in organic azides) to ∼86
kcal mol
–1 comparable with an energy
of the C–C covalent bonds. The thermodynamics of the anions’
coordination to 1 and their Se and S congeners was also
studied by quantum chemical calculations. The general character of
this reaction and favorable thermodynamics in the case of heavier
chalcogens (Se, Te) were established. Comparison with available data
on acyclic analogues, i.e. the chalcogen diimines RNXNR,
reveals that they also coordinate various anions but in addition reactions
across XN (X = S, Se, Te) double bonds. Attempts to prepare
the anion [1-TePh]− led to disintegration
of 1. The only unambiguously identified product was a
rather rare tellurocyanate that was characterized by XRD and elemental
analysis as the salt [K(18-crown-6)]+[TeCN]− (13).
“…This approach is an extension of the chalcogen tetrahalide based methodology, previously suggested for the synthesis of 2,1,3-benzochalcogenadiazoles, to non-benzoid systems (chalcogen tetrahalides are SF 4 , SeCl 4 , and TeCl 4 ). [15] Unexpectedly, compound 1 was isolated from the reaction mixture in the form of a 1:1 complex with pyridinium chloride (5; Scheme 2). Pure 1, which was obtained by decomposition of complex 5 with water, was found to be thermally stable and stable to air in both the solid state and in solution.…”
Dedicated to Professor Neil Bartlett on the occasion of his 75th birthday
IntroductionChalcogen-nitrogen chemistry [1] has begun to play an increasingly important role in the design and synthesis of [a]
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