Intramolecular Singlet Fission in an Antiaromatic Polycyclic Hydrocarbon

Wu, Yishi; Wang, Yuancheng; Chen, Jianwei; Zhang, Guanxin; Yao, Jiannian; Zhang, Deqing; Fu, Hongbing

doi:10.1002/anie.201704668

Cited by 66 publications

(51 citation statements)

References 47 publications

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“…A drawback with pentalenes are their transitions to the S1 state which are forbidden or very weakly allowed (for calculated oscillator strengths see Table S19), although excitation to the S2 state in a 5,10bis(styryl) substituted dibenzo[a,e]pentalene has shown to provide an entry point to singlet fission. 79 The monobenzannelation in BENZPENT1 increases E(T1) when compared to the parent pentalene ( Figure 11), similar as found for CBD and BENZCBD1, but BENZPENT1…”

Section: Earlier Experimentally Investigated Fulvenessupporting

confidence: 66%

Strategies for Design of Potential Singlet Fission Chromophores Utilizing Baird's Rule on Excited State Aromaticity

O¹,

Smith²,

Ottosson

2019

Preprint

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In singlet exciton fission one photon of light is used to create two excitons of triplet multiplicity. This process requires chromophores with their lowest excited states arranged so that 2E(T1) < E(S1) and E(S1) < E(T2). To match different technology platforms there is a high need for new candidate chromophores with the desired excited state orderings. Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird’s 4n rule on excited state aromaticity to tailor new potential chromophores for singlet fission. We first analyze the E(T1), E(S1) and E(T2) of benzene and cyclobutadiene (CBD) as, respectively, excited state antiaromatic and aromatic archetypes, and reveal that CBD fulfils the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned from Baird-antiaromatic to Baird-aromatic in T1 and S1 by choice of substituents. The T1 and S1 states of fulvenes are both described by singly excited HOMO→LUMO configurations, which provides a rational for the simultaneous and similar tuning of E(T1) and E(S1) along an approximate (anti)aromaticity coordinate. This leads us to a geometric model for identification of singlet fission chromophores. Candidates with calculated E(T1) of ~1 eV or higher are also identified among benzannelated 4npi-electron compound classes and among siloles influenced to various extents by Baird-(anti)aromaticity in T1 and S1. Finally, we explore the limitations of the design approach. In brief, it is clarified how Baird’s 4n rule together with substituent effects (electronic and steric) and benzannelation can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

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Section: Earlier Experimentally Investigated Fulvenessupporting

confidence: 66%

Strategies for Design of Potential Singlet Fission Chromophores Utilizing Baird's Rule on Excited State Aromaticity

O¹,

Smith²,

Ottosson

2019

Preprint

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“…Although iSF can be treated as a special IC process, we note that it is important to distinguish iSF from the latter. Based on aforementioned results, we propose a preliminary design ideas for potential iSF‐capable materials: a) weak fluorescence property (another dominant deactivation outcompetes emission process), b) biradicaloid structure to satisfy the energetic condition for SF process (E(S 1 )≈2×E(T 1 )), and c) symmetry skeleton to hold the intramolecular multiexciton pair …”

Section: Figurementioning

confidence: 99%

Revealing the Nature of Singlet Fission under the Veil of Internal Conversion

Wang

Bai

et al. 2019

Angew Chem Int Ed

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Singlet fission (SF) holds the potential to boost the maximum power conversion efficiency of photovoltaic devices. Internal conversion (IC) has been considered as one of the major competitive deactivation pathwayst ot ransform excitation energy into heat. Now, using time-resolved spectroscopy and theoretical calculation, it is demonstrated that, instead of ac onventional IC pathway,a nu nexpected intramolecular singlet fission (iSF) process is responsible for excited state deactivation in isoindigo derivatives.The 1 TT state could form at ultrafast rate and nearly quantitatively in solution. In solid films,t he slipped stacked intermolecular packingo fathiophene-functionalized derivative leads to efficient triplet pair separation, giving rise to an overall triplet yield of 181 %. This work not only enriches the pool of iSF-capable materials,b ut also contributes to ab etter understanding of the iSF mechanism, whichcould be relevant for designing new SF sensitizers.Singlet fission (SF) is aphotophysical process that converts one high-energy singlet into two low-energy triplets. [1] Therefore,SFcan potentially offset the thermal losses and enhance the maximum power conversion efficiency of photovoltaic devices. [1][2][3] Theenergetic requirement of E(S 1 ) % 2 E(T 1 )by an efficient SF process is not frequently met in most organic molecules.C onsequently,o nly ah andful of molecules are known to fulfil this thermodynamic condition, including tetracene, [4] pentacene, [5] some of their derivatives, [6] perylenediimide, [7] oligoenes, [8] and donor-acceptor polymers. [9] SF has been implemented in photovoltaic device and peak external quantum efficiency above 100 %h as been obtained. [10] Thek ey parameter of SF is the ultimate yield of independent free triplets that can be harnessed by photovoltaic devices.T his means SF should outcompete with other excitation-deactivation processes.SFoften occurs on 100 fs to ps timescale as aresult of its spin-conserved primary event of (S 1 S 0 )-to-1 (TT). [1,3] In some cases,i nternal conversion (IC), an onradiative transition between two electronic states with the same multiplicity,r epresents ac ompetition excitationdeactivation channel. [11] Overall, SF serves as an excitonmultiplication process,w hereas IC is an excitation-energyloss channel. Formany candidates theoretically predicted for SF,i ti sI C, rather than SF,t hat dominates the major deactivation process. [1a, 12] Therefore,d istinguishing SF from IC is very important for the development and optimization of new SF-capable materials.Isoindigo has attracted ag reat deal of attention as the electron-acceptor components for optoelectronic materials. [13] Similar to its structural isomer of indigo,isoindigo derivatives are also weakly emissive.F or al ong time,t he rapid nonradiative deactivation in both indigos and isoindigos has been assigned to conventional IC process. [14] Based on their favorable excited-state energies,M ichl et al. have postulated the possibility of SF in these compounds. [1a] Recently,Xia a...

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“…As a proof‐of‐concept study, we selected pentalene, one of the representative antiaromatic compounds with 8π electrons in the periphery, as a core 4nπ‐electron scaffold. Whereas pristine pentalene 1 and its methyl‐substituted derivatives are thermally labile compounds that undergo dimerization even at low temperatures, [20] kinetic stabilization by the introduction of bulky substituents [21] or thermodynamic stabilization by the annulation of aromatic rings [22‐25] enabled access to various pentalene derivatives. In particular, dibenzo[ a , e ]pentalene (DBP) derivatives 2 have been actively studied from a wide range of perspectives, including the development of new synthetic methods [22, 23] and the investigation of their properties, such as semiconducting properties [5a,b,d‐f] and singlet fission [24] .…”

Section: Introductionmentioning

confidence: 99%

Dithieno[a,e]pentalenes: Highly Antiaromatic Yet Stable π‐Electron Systems without Bulky Substituents

Usuba

Hayakawa

Yamaguchi

et al. 2020

Chemistry A European J

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Dithieno[a,e]penalenes (DTPs) with various substituents were synthesized as a class of antiaromatic compounds. Annulation of thiophene rings imparts the pentalene moiety with high thermal stability even without bulky substituents, while retaining antiaromaticity. The higher magnitude of antiaromaticity in DTPs, in addition to the differences in the electronic structures of the fused aromatic rings, resulted in a narrower HOMO–LUMO gap than that of the corresponding dibenzo[a,e]pentalene analog, giving rise to red‐shifted electronic absorption that reaches the near‐infrared region. Moreover, systematic investigations on the solid‐state packing structure revealed that DTPs prefer offset face‐to‐face packing motifs rather than face‐centered π–π stacking. In particular, the thienyl‐substituted DTP bearing hydrophilic side chains exhibited thermochromic behavior in polar solvents, which was ascribed to the formation of aggregates.

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Intramolecular Singlet Fission in an Antiaromatic Polycyclic Hydrocarbon

Cited by 66 publications

References 47 publications

Strategies for Design of Potential Singlet Fission Chromophores Utilizing Baird's Rule on Excited State Aromaticity

Strategies for Design of Potential Singlet Fission Chromophores Utilizing Baird's Rule on Excited State Aromaticity

Revealing the Nature of Singlet Fission under the Veil of Internal Conversion

Dithieno[a,e]pentalenes: Highly Antiaromatic Yet Stable π‐Electron Systems without Bulky Substituents

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