Electron transfer within 1,3‐dinitrobenzene radical anions: electron hopping or superexchange?

Moneo, Álvaro; Telo, João P.

doi:10.1002/poc.2957

Cited by 5 publications

(2 citation statements)

References 44 publications

(68 reference statements)

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“…(1) At 295 K, the HT rate constants of all mX compounds are an order of magnitude smaller than those of the pX compounds. This qualitatively agrees with general observations made before for other MV compounds in a similar context . (2) The rate constants are almost independent of the substituents within the mX series.…”

Section: Resultssupporting

confidence: 92%

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

et al. 2017

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To address the question whether donor substituents can be utilized to accelerate the hole transfer (HT) between redox sites attached in para- or in meta-positions to a central benzene bridge, we investigated three series of mixed valence compounds based on triarylamine redox centers that are connected to a benzene bridge via alkyne spacers at para- and meta-positions. The electron density at the bridge was tuned by substituents with different electron donating or accepting character. By analyzing optical spectra and by DFT computations we show that the HT properties are independent of bridge substituents for one of the meta-series, while donor substituents can strongly decrease the intrinsic barrier in the case of the para-series. In stark contrast, temperature-dependent ESR measurements demonstrate a dramatic increase of both the apparent barrier and the rate of HT for strong donor substituents in the para-cases. This is caused by an unprecedented substituent-dependent change of the HT mechanism from that described by transition state theory to a regime controlled by solvent dynamics. For solvents with slow longitudinal relaxation (PhNO, oDCB), this adds an additional contribution to the intrinsic barrier via the dielectric relaxation process. Attaching the donor substituents to the bridge at positions where the molecular orbital coefficients are large accelerates the HT rate for meta-conjugated compounds just as for the para-series. This effect demonstrates that the para-meta paradigm no longer holds if appropriate substituents and substitution patterns are chosen, thereby considerably broadening the applicability of meta-topologies for optoelectronic applications.

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Section: Resultssupporting

confidence: 92%

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

et al. 2017

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“… Increasing electronic coupling lowers the activation energies for the forward (Δ G f *) and backward (Δ G r *) reactions, consequently, accelerating thermal electron transfer in both directions. It is remarkable that based on the semiclassical theories, the ET kinetics and dynamics in MV systems may be determined by optical analyses. − However, reports on full optical determination of ET rates for D–B–A systems are limited, , especially in asymmetrical systems. Troubles in practical application of the theories and methodologies include assignments of the intervalence bands, and completeness and reliability of the energetic data.…”

Section: Introductionmentioning

confidence: 99%

Optical Determination of Electron Transfer Dynamics and Kinetics for Asymmetrical [Mo₂]–ph–[Mo₂] Systems

Meng

Lei

et al. 2016

J. Phys. Chem. C

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We report the study, in terms of electronic coupling (EC) and electron transfer (ET), on three asymmetrical Mo 2 dimers [Mo 2 (DAniF) and [Mo 2 (DAniF) 3 ] 2 [μ-(NH) 2 CC 6 H 4 C(NH)O] ([NN−ph− NO]), which are closely related to the three symmetrical analogues [OO− ph−OO], [NO−ph−NO], and [NN−ph−NN] reported earlier. The mixedvalence (MV) complexes [NO−ph−OO] + , [NN−ph−OO] + , and [NN−ph− NO] + exhibit metal to ligand and ligand to metal charge transfer bands, along with an intervalence (IV) transition absorption in the Near-IR region. The free energy change (ΔG°) for ET is determined by comparing the redox potential splitting (ΔE 1/2 ) and IV transition energy (E IT ) with the data for the symmetrical species. The reorganization energy (λ) is estimated from the Hush model (Δν 1/2 = [16ln( 2)λRT] 1/2 ). Significantly, electrochemical and optical analyses verify E IT = ΔG°+ λ, the core energetic relationship underlying the semiclassical theories. With the electronic coupling parameters calculated from the method suggested by Creutz, Newton and Sutin (H MM′ = ∼ 500 cm −1 ), the adiabatic ET rate constants k et (f) are determined to be ∼10 10 s −1 for [NO−ph−OO] + and [NN−ph−NO] + , smaller than k et (r) for the backward reaction and k et for the symmetrical analogues by 1 order of magnitude, and ∼10 9 s −1 for [NN−ph−OO] + . This work illustrates that the redox asymmetry in D−B− A systems controls the ET rate and direction.

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Intramolecular Charge Transfer in Kekulé‐ and Non‐Kekulé‐Bridged Bis(triarylamine) Radical Cations: Missing Key Compounds in Organic Mixed‐Valence Systems

Uebe

Ito

2019

Chemistry An Asian Journal

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From the viewpoint of para-meta topological bridging effect on the electronic coupling in organic mixed-valence( MV) systems, the optically induceda nd thermally assisted intramolecular charge/spin transfer (ICT/IST) processesh ave been investigated for three bis(triarylamine)( BTA) radical cations as missing key compounds in very basic BTAM Vs ystems. In contrast to the case of p-a nd m-dinitrobenzene radicala nions, the difference in the strength of electronic coupling (V)w as not so large for the present BTAM Vr adicalc ations,a lthough they still fall within the paradigm of strong V for para-linkage and weak V for meta-linkage. Unexpectedly,i th as been found that meta-phenylenediamine radical cation has an electronic coupling comparable to those in the para-conjugated BTA-based MV species, and the ICT/IST rate exceeds the ESR time-scale. This finding is very encouraging considering that sufficient electronic communication can be ensured even when the redox-active centers are linked directly by the meta-phenylene bridge, thus broadening the selection of p-bridging units for moleculebased optoelectronics.Recent progress in organic mixed-valence( MV) chemistry has conduced aw ealth of understanding of basic electron-and/or charge-transfer (ET/CT) phenomena. [1] In particular, bis(triarylamine) (BTA) radicalc ations are considered as versatile model systemsf or probing into variousa spects of electronic coupling between the neutral and chargedr edox-activec enterst hrough av ariety of p-bridging units (Scheme 1a). [1,6, 7] The strength of electronic coupling (V)i sm ainly determined by the type of aromatic bridge and the substitution pattern:i nt he case of unsubstituted phenylene bridge, para-phenylene ensures a Scheme1.(a) Schematic drawing of BTA-based MV compound, (b) para-and meta-dinitrobenzene radicalanions, and (c) the key BTA-based MV compounds.[a] Dr.M.U ebe,

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Electron transfer within 1,3‐dinitrobenzene radical anions: electron hopping or superexchange?

Cited by 5 publications

References 44 publications

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

Optical Determination of Electron Transfer Dynamics and Kinetics for Asymmetrical [Mo₂]–ph–[Mo₂] Systems

Intramolecular Charge Transfer in Kekulé‐ and Non‐Kekulé‐Bridged Bis(triarylamine) Radical Cations: Missing Key Compounds in Organic Mixed‐Valence Systems

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Electron transfer within 1,3‐dinitrobenzene radical anions: electron hopping or superexchange?

Cited by 5 publications

References 44 publications

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

Hole Transfer Processes inmeta-andpara-Conjugated Mixed Valence Compounds: Unforeseen Effects of Bridge Substituents and Solvent Dynamics

Optical Determination of Electron Transfer Dynamics and Kinetics for Asymmetrical [Mo2]–ph–[Mo2] Systems

Intramolecular Charge Transfer in Kekulé‐ and Non‐Kekulé‐Bridged Bis(triarylamine) Radical Cations: Missing Key Compounds in Organic Mixed‐Valence Systems

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Optical Determination of Electron Transfer Dynamics and Kinetics for Asymmetrical [Mo₂]–ph–[Mo₂] Systems