An insight on the aromatic changes in closed shell icosagen, tetrel, and pnictogen phenalenyl derivatives

One of the recent proposals for the design of state-of-the-art emissive materials for organic light emitting diodes (OLEDs) is the principle of thermally activated delayed fluorescence (TADF). The underlying idea is to enable facile thermal upconversion of excited state triplets, which are generated upon electron-hole recombination, to excited state singlets by minimizing the corresponding energy difference resulting in devices with up to 100% internal quantum efficiencies (IQEs). Ideal emissive materials potentially surpassing TADF emitters should have both negative singlet-triplet gaps and appreciable fluorescence rates to maximize reverse intersystem crossing (rISC) rates from excited triplets to singlets while minimizing ISC rates and triplet state occupation leading to long-term operational stability. However, molecules with negative singlet-triplet gaps are extremely rare and, to the best of our knowledge, not emissive. In this work, based on computational studies, we describe the first molecules with negative singlet-triplet gaps and considerable fluorescence rates and show that they are more common than hypothesized previously. File list (2) download file view on ChemRxiv manuscript.pdf (1.92 MiB) download file view on ChemRxiv supporting.pdf (338.61 KiB)

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“…20 Moreover, the possibility of inverted singlet-triplet gaps but in higher excited states was also investigated. 21…”

Section: Introductionmentioning

confidence: 99%

Organic molecules with inverted gaps between first excited singlet and triplet states and appreciable fluorescence rates

Pollice

Friederich

Lavigne

et al. 2021

Matter

101

181

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“…Scientific literature already contains some on-the-road rethinking and rebranding: “group 18 bonds” introduced as “aerogen bond” 11 became more IUPAC-endorsed-like “noble gas bond”; 20 “triel bond” 10 /“icosagen bond” 45 duality; “regium” 18 /“coinage” 17 /“metallophilic” pastiche, etc . ; some terminology mishmash could be unavoidable during the considerable effort of establishing a new consistent and unambiguous terminology.…”

Section: A Primer In Novel Nomenclaturementioning

confidence: 99%

Ye Olde supramolecular chemistry, its modern rebranding and overarching trends in chemistry

Savastano

2024

Dalton Trans.

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“…[15] The more accurate NICS zz scan was used to confirm the anti-aromaticity of N[3.3.3]. [16,17] Also Krygowski's geometry-based HOMA-index (harmonic oscillator model of aromaticity) was employed to determine the antiaromaticity of N[3.3.3]; [18] employing adequately calculated resonance energies of some cyclazines instead was less successful. [19] But if system planarity and the common peripheral ring current of the three ring moieties are given up (in twisted, non-planar, bowl-shaped structures), the NICS index does not help; when still applied, conclusions remained like the cyclazine is aromatic and anti-aromatic [15] or Hückel's rule is difficult to apply to non-planar cyclazines [17] which are not productive.…”

Section: 3] N[333] N[234]mentioning

confidence: 99%

“…After the pioneering introduction of the nucleus‐independent chemical shift (NICS) concept by Paul von Ragué Schleyer, [13,14] the aromaticity or anti‐aromaticity of cyclazines was defined by NICS(0) and NICS(1) values, [15] beside other theoretical items like magnetic susceptibility or the HOMO‐LUMO gap [15] . The more accurate NICS zz scan was used to confirm the anti‐aromaticity of N[3.3.3] [16,17] …”

Section: Introductionmentioning

confidence: 99%

“…But if system planarity and the common peripheral ring current of the three ring moieties are given up (in twisted, non‐planar, bowl‐shaped structures), the NICS index does not help; when still applied, conclusions remained like the cyclazine is aromatic and anti‐aromatic [15] or Hückel's rule is difficult to apply to non‐planar cyclazines [17] which are not productive.…”

Section: Introductionmentioning

confidence: 99%

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Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

Kleinpeter

Koch

2022

Eur J Org Chem

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Structure and spatial magnetic properties, through‐space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero‐analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6‐311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in 1H NMR spectroscopy) are visualized as iso‐chemical‐shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [δ(1H)/ppm, δ(15N)/ppm] and geometry (planar, twisted, bow‐shaped) data. The cyclazines N[2.2.2]− up to N[2.4.4]− are planar or at most slightly bowl‐shaped and, due to coherent peripheral ring currents (except in N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+), develop aromaticity or anti‐aromaticity of the whole molecules dependent on the number of peripheral conjugated π electrons. The cyclazines N[2.3.3]−, N[2.3.4], N[3.3.4]+ and N[2.4.4]+ develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4]+ diatropic) including the nodal N pz lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4]− and N[4.4.4]+ are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated π electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Hückel's rule.

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An insight on the aromatic changes in closed shell icosagen, tetrel, and pnictogen phenalenyl derivatives

Cited by 11 publications

References 110 publications

Organic molecules with inverted gaps between first excited singlet and triplet states and appreciable fluorescence rates

Organic molecules with inverted gaps between first excited singlet and triplet states and appreciable fluorescence rates

Ye Olde supramolecular chemistry, its modern rebranding and overarching trends in chemistry

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

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