Deciphering the role of (anti)aromaticity in cofacial excimers of linear acenes

Krishnan, A.; Diaz‐Andres, Aitor; Sudhakaran, Keerthy P.; John, Athira T.; Hariharan, Mahesh; Casanova, David

doi:10.1002/poc.4438

Cited by 8 publications

(8 citation statements)

References 47 publications

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“…The excited‐state homoaromatic characters of these latter species were examined based on various aromaticity indicators including C⋅⋅⋅C homoconjugative distances ( r (C⋅⋅⋅C)), ACID plots, NICS scans and ISE values in the T 1 state, and r (C⋅⋅⋅C) in the S 1 state. In general, this Baird homoaromaticity should provide extra stabilization to photochemical reaction intermediates, [172] and similar through‐space conjugation leading to excited‐state homoaromaticity has been used to rationalize computational findings on exciplex formation in the T 1 states of benzene, naphthalene and anthracene [173,174] …”

Section: Relief Of Esaamentioning

confidence: 99%

“…[172] and similar through-space conjugation leading to excited-state homoaromaticity has been used to rationalize computational findings on exciplex formation in the T 1 states of benzene, naphthalene and anthracene. [173,174] In addition to protonation, the ESAA character of benzene in T 1 can be diminished through hydrogen atom abstraction from triethylhydrosilane by benzene as also this breaks the cyclic π-conjugation (Figure 19A). [102] Thus, Baird-antiaromatic [4n + 2]annulenes should be susceptible to photochemical addition reactions (cf.…”

Section: Chemistry-a European Journalmentioning

confidence: 99%

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Photochemistry Driven by Excited‐State Aromaticity Gain or Antiaromaticity Relief

Yan

Slanina

Bergman

et al. 2023

Chemistry A European J

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Gain of aromaticity or relief of antiaromaticity along a reaction path are important factors to consider in mechanism studies. Analysis of such changes along potential energy surfaces has historically focused on reactions in the electronic ground state (S 0 ), but can also be used for excited states. In the lowest ππ* states, the electron counts for aromaticity and antiaromaticity follow Baird's rule where 4n π-electrons indicate aromaticity and 4n + 2 π-electrons antiaromaticity. Yet, there are also cases where Hückel's rule plays a role in the excited state. The electron count reversals of Baird's rule compared to Hückel's rule explain many altered physicochemical properties upon excitation of (hetero)annulene derivatives. Here we illustrate how the gain of excited-state aromaticity (ESA) and relief of excited-state antiaromaticity (ESAA) have an impact on photoreactivity and photostability. Emphasis is placed on recent findings supported by the results of quantum chemical calculations, and photoreactions in a wide variety of areas are covered.

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Section: Relief Of Esaamentioning

confidence: 99%

Section: Chemistry-a European Journalmentioning

confidence: 99%

Photochemistry Driven by Excited‐State Aromaticity Gain or Antiaromaticity Relief

Yan

Slanina

Bergman

et al. 2023

Chemistry A European J

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“…As the exciton states of molecular aggregates are linear combinations of local (intramolecular) excitations (

) and charge transfer (

) (i.e., intermolecular) excitations, such intramolecular and intermolecular excitations represent a convenient set of diabatic states that can be exploited to analyze the character of the exciton/excimer states [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. Thus, seeking to uncover the nature of the excimer states, we use a diabatization procedure to capture the contribution of the

states, crucial in the formation of excimers [ 51 , 52 , 53 ], and to unveil the most relevant intermolecular interactions.…”

Section: Introductionmentioning

confidence: 99%

Eclipsed and Twisted Excimers of Pyrene and 2-Azapyrene: How Nitrogen Substitution Impacts Excimer Emission

Dai,

Rambaldi,

Negri

2024

Molecules

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Due to their unique photophysical and electronic properties, pyrene and its analogues have been the subject of extensive research in recent decades. The propensity of pyrene and its derivatives to form excimers has found wide application in various fields. Nitrogen-substituted pyrene derivatives display similar photophysical properties, but for them, excimer emission has not been reported to date. Here, we use time-dependent density functional theory (TD-DFT) calculations to investigate the low-lying exciton states of dimers of pyrene and 2-azapyrene. The excimer equilibrium structures are determined and the contribution of charge transfer (CT) excitations and intermolecular interactions to the exciton states is disclosed using a diabatization procedure. The study reveals that the dimers formed by the two molecules have quite similar exciton-state patterns, in which the relevant CT contributions govern the formation of excimer states, along with the La/Lb state inversion. In contrast with pyrene, the dipole–dipole interactions in 2-azapyrene stabilize the dark eclipsed excimer structure and increase the barrier for conversion into a bright twisted excimer. It is suggested that these differences in the nitrogen-substituted derivative might influence the excimer emission properties.

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“…DTP cores substituted with electron-donating and accepting groups can be used as p-and n-type organic semiconductors, respectively. 16 Our ongoing interest in tuning the antiaromaticity 20,21 and charge transport properties 22 of supramolecular systems motivated us to explore the influence of graphene fragments 23,24 on the antiaromaticity of pentalene through p-p interactions. The antiaromaticity of pentalene was evaluated in terms of nucleus independent chemical shift (NICS), [25][26][27][28][29][30] gauge including the magnetically induced current (GIMIC), [31][32][33] anisotropy of the induced current density (AICD), 34,35 harmonic oscillator model of aromaticity (HOMA) 36,37 and aromatic fluctuation index (FLU).…”

mentioning

confidence: 99%