New insights into the design of conjugated polymers for intramolecular singlet fission

Hu, Jiahua; Xu, Ke; Shen, Lei; Wu, Qin; He, Guiying; Wang, Jieyu; Pei, Jian; Xia, Jianlong; Sfeir, Matthew Y.

doi:10.1038/s41467-018-05389-w

Cited by 108 publications

(144 citation statements)

References 49 publications

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“…Furthermore, transient PL measurements (Supporting Information, Figure S11) also detected emissions from 1 (TT), which decays with almost same lifetimes as those of ESA features in fsTA measurements (Figure b). Xia and Sfeir et al . reported similar results supporting ultrafast iSF process in donor–acceptor copolymers composed of isoindigo and bithiophene moieties.…”

Section: Figurementioning

confidence: 53%

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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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Section: Figurementioning

confidence: 53%

“…Recently, Xia and Sfeir et al. reported a highly efficient iSF process occurred in donor–acceptor copolymers based on isoindigo and bithiophene . These results suggest isoindigo compounds may play an important role in developing SF‐capable materials.…”

Section: Figurementioning

confidence: 94%

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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“…8). Because the C=C stretching motions primarily vibrate along the π-conjugation pathway, their IR-activities are sensitive to structural distortion 20 . The C=C stretching motions in aromatic skeletons take place along planar and symmetric molecular frameworks carrying out negligible (null) change of dipole moment, which leads to very weak (forbidden) IR absorption bands.…”

Section: Resultsmentioning

confidence: 99%

“…In other words, understanding the role of aromaticity in the excited states enables the mechanistic elucidation of photoinduced electronic properties 1,2,15 . In this regard, shifts of π-electron density during the formation of photo-activated intermediate states, such as charge transfer/separation and multiple exciton/charge generation 16–20 , can be driven by changes of aromaticity. Recent intensive efforts by optical and transient spectroscopic analyses have paved the way to unravel the effect of excited-state aromaticity 14,21–23 .…”

Section: Introductionmentioning

confidence: 99%

Two-electron transfer stabilized by excited-state aromatization

Kim

Park

et al. 2019

Nat Commun

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The scientific significance of excited-state aromaticity concerns with the elucidation of processes and properties in the excited states. Here, we focus on TMTQ, an oligomer composed of a central 1,6-methano[10]annulene and 5-dicyanomethyl-thiophene peripheries (acceptor-donor-acceptor system), and investigate a two-electron transfer process dominantly stabilized by an aromatization in the low-energy lying excited state. Our spectroscopic measurements quantitatively observe the shift of two π-electrons between donor and acceptors. It is revealed that this two-electron transfer process accompanies the excited-state aromatization, producing a Baird aromatic 8π core annulene in TMTQ. Biradical character on each terminal dicyanomethylene group of TMTQ allows a pseudo triplet-like configuration on the 8π core annulene with multiexcitonic nature, which stabilizes the energetically unfavorable two-charge separated state by the formation of Baird aromatic core annulene. This finding provides a comprehensive understanding of the role of excited-state aromaticity and insight to designing functional photoactive materials.

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“…In SF the absorption of a single photon ideally results in the formation of two spatially separated triplet excitons [9][10][11][12] , although a concerted sequence of ultrafast electronic and vibrational dynamics must compete with both radiative and non-radiative losses for this exciton multiplication to be efficient enough for applications [13][14][15][16][17] . Observation, understanding and control of these many-body quantum dynamics is therefore essential for optimisation of conjugated molecules for technologies such as SFenhanced PVs [18][19][20][21] .…”

Section: Introductionmentioning

confidence: 99%

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S1 (21Ag-) State of Pi-Conjugated Systems

Pandya

Rao

2019

Proceedings of the nanoGe Fall Meeting 2019

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The S1 (2 1 Ag -) state is an optically dark state of natural and synthetic pi-conjugated materials that can play a critical role in optoelectronic processes such as, energy harvesting, photoprotection and singlet fission. Despite this widespread importance, direct experimental characterisations of the electronic structure of the S1 (2 1 Ag -) wavefunction have remained scarce and uncertain, although advanced theory predicts it to have a rich multi-excitonic character. Here, studying an archetypal polymer, polydiacetylene, and carotenoids, we experimentally demonstrate that S1 (2 1 Ag -) is a superposition state with strong contributions from spin-entangled pairs of triplet excitons ( 1 (TT)). We further show that optical manipulation of the S1 (2 1 Ag -) wavefunction using triplet absorption transitions allows selective projection of the 1 (TT) component into a manifold of spatially separated triplet-pairs with lifetimes enhanced by up to one order of magnitude and whose yield is strongly dependent on the level of interchromophore coupling. Our results provide a unified picture of 2 1 Agstates in pi-conjugated materials and open new routes to exploit their dynamics in singlet fission, photobiology and for the generation of entangled (spin-1) particles for molecular quantum technologies.

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New insights into the design of conjugated polymers for intramolecular singlet fission

Cited by 108 publications

References 49 publications

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

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

Two-electron transfer stabilized by excited-state aromatization

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S1 (21Ag-) State of Pi-Conjugated Systems

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