The Low-Lying Electronic States of Pentacene and Their Roles in Singlet Fission

Zeng, Tao; Hoffmann, Roald; Ananth, Nandini

doi:10.1021/ja500887a

Cited by 218 publications

(397 citation statements)

References 76 publications

(196 reference statements)

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“…By plotting the extinction coefficients as a function of concentration, we noticed a saturation behavior towards the high concentration regime. At an extrapolation to 5 × 10 To substantiate our postulate we performed actinometry using pristine C 60 . 69 Here, we used solutions of pristine C 60 with four different concentrations and solutions of either 7, XC1, or XC2, each of them with exactly the same absorptions at the 387 nm excitation wavelength, and pumped them with the same laser power.…”

Section: Triplet-triplet Sensitizationmentioning

confidence: 85%

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

et al. 2016

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aWe show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 10 12 s −1, respectively, in room temperature solutions.

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Section: Triplet-triplet Sensitizationmentioning

confidence: 85%

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

et al. 2016

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“…The first steps towards this goal have been taken with the demonstration of organic solar cells based on pentacene, that show external quantum efficiencies above 129%, the highest for any solar technology to date. 4,5 Despite advances in the experimental characterization of SF in several molecular systems [6][7][8][9][10][11][12][13] as well as extensive theoretical work, 1, 14-22 the fundamental mechanism of ultrafast SF remains unclear. In the kinetic model proposed by Merrifield and co-workers 23 !…”

Section: " "mentioning

confidence: 99%

Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy

et al. 2015

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Abstract:Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spintriplet excitons residing on neighbouring molecules. To rationalise this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesised as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast 2D electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons.The resulting manifold of vibronic states drives sub-100-fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems. 2" "Singlet fission (SF) is an exciton multiplication process in organic semiconductors that allows one photogenerated spin-singlet excited state to be converted to two spin-triplet excitons.1 !The two generated spin-triplet excitons are initially correlated to form an overall spin-singlet state, making SF a spin-allowed process in contrast to intersystem crossing that involves a spin flip. For systems where the energy of the lowest lying singlet exciton (S) is close to double the energy of the triplet state (T), such as pentacene and its derivatives, SF can occur on a sub-100fs timescale with every singlet being converted to two triplets.2 SF has attracted great attention lately as it enables photovoltaic devices to overcome thermalisation losses by generating two electron-hole pairs per high-energy photon absorbed, potentially allowing single-junction devices that could beat the Shockley-Queisser limit on power conversion efficiency 3 . The first steps towards this goal have been taken with the demonstration of organic solar cells based on pentacene, that show external quantum efficiencies above 129%, the highest for any solar technology to date. 4,5 Despite advances in the experimental characterization of SF in several molecular systems 6-13 as well as extensive theoretical work, 1, 14-22 the fundamental mechanism of ultrafast SF remains unclear. In the kinetic model proposed by Merrifield and co-workers 23 ! the process can be represented as S!TT!T+TWhere: S is the lowest singlet excited singlet state, T is the molecular triplet state and T+T is a pair of fully independent T states. TT corresponds to a doubly excited pair of spin-correlated triplets, forming an overall spin singlet. The TT state, often referred to as the multiexciton state, is considered a dark state that cannot be optically populated from the ground state g, but serves as an intermediate to the formation of free independent triplets T+T.Current theoretical models for SF focus on characterising t...

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“…Unfortunately, this dark state is particularly important to researchers as it has been proposed as a crucial intermediate in the process of singlet fission (33). Only some expensive multireference methods (32,33,(72)(73)(74) have hitherto been applied to describe this 1 A g state for small acenes, but these methods are not feasible for higher acenes because of the computational cost. Very recently, the DFT-based multireference configuration interaction method (DFT/MRCI) has been applied to the excited states of higher acenes up to 9 and achieved good accuracy (63).…”

Section: Significancementioning

confidence: 99%

Nature of ground and electronic excited states of higher acenes

Yang

Davidson

Yang

2016

Proc. Natl. Acad. Sci. U.S.A.

174

208

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Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particleparticle random-phase approximation calculation. The 1 A g ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state 3 B 2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state 1 B 2u is a zwitterionic state to the short axis. The excited 1 A g state gradually switches from a doubleexcitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the 1 B 2u and excited 1 A g states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved.higher acenes | diradical | double excitation | particle-particle random-phase approximation | charge-transfer excitation

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The Low-Lying Electronic States of Pentacene and Their Roles in Singlet Fission

Cited by 218 publications

References 76 publications

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy

Nature of ground and electronic excited states of higher acenes

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