Diradical Character-Based Design for Singlet Fission of Bisanthene

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Letter

Diradical Character Based Design for Singlet Fission of Bisanthene Derivatives: Aromatic-Ring Attachment and #-Plane Twisting Soichi Ito, Takanori Nagami, and Masayoshi Nakano J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b01885 • Publication Date (Web): 16 Sep 2016 Downloaded from http://pubs.acs.org on September 16, 2016

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The Journal of Physical Chemistry Letters

Diradical Character Based Design for Singlet Fission of Bisanthene Derivatives: Aromatic-Ring Attachment and π-Plane Twisting

Soichi Ito, Takanori Nagami, and Masayoshi Nakano* Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan [email protected] Tel: +81-6-6850-6265

ABSTRACT:

We demonstrate a diradical character based molecular design for singlet

fission using polycyclic aromatic hydrocarbons, bisanthene derivatives.

Two types of

chemical modifications – aromatic-ring attachment and π-plane twisting – are examined in order to satisfy the energy level matching condition for singlet fission.

Detailed analysis of

the electronic structures of the model molecules using nucleus independent chemical shift, molecular orbitals and their energies has demonstrated the usefulness of the relationship between the resonance structure and aromaticity, and that between non-planarity of π-conjugated systems and reduction of orbital overlap for tuning the diradical character. This result provides a novel design guideline for polycyclic aromatic hydrocarbons toward efficient singlet fission. TOC graphic

O

O

F

F

F

F

Diradical character y0 Energy loss |2E(T1) – E(S1)|

Isoergic Singlet Fission 1 ACS Paragon Plus Environment


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Singlet fission1,2 (SF), where a singlet exciton splits into two triplet excitons, is expected to enhance the photo-current energy conversion efficiency from the conventional value of 33% up to 47%.3

This promising application has motivated broad areas of

researchers to reinvestigate this old phenomena found in 1965.4

Furthermore, in 2015, Liu

et al. have shown another application of SF to efficient non-linear optical responses.5 Unfortunately, although these promising applications of SF were presented, most researches of SF have focused on photophysical studies using only a limited number of compounds such as tetracene,6–9 pentacene,8–14 perylenebisimide,15–17 1,3-diphenylisobenzofuran.18,19

To

realize the above applications, a vast survey in a wide range of molecules must be conducted.20–27

From the standpoint of molecular design for SF, the energy level matching

is considered to be fundamental to SF,1 where there are two conditions: (i) the lowest singlet excitation energy is higher than twice the lowest triplet excitation energy, 2E(T1) – E(S1) < 0, and (ii) the second lowest excitation energy is higher than twice the lowest triplet excitation energy, 2E(T1) – E(T2) < 0.

The first condition is required for SF process S1 → 2T1 to be

exothermic, while the second for the reverse process, triplet-triplet annihilation 2T1 → T2, to be endothermic.

Smith and Michl proposed that diradicaloids and alternant hydrocarbons

are promising candidates for SF,1 and then we have found that these two design guidelines could be unified and could be represented quantitatively using the multiple diradical character yi (i = 0, 1, ...),20 which characterizes the open-shell singlet nature of a molecule, or represents the instability of a chemical bond.28, 29

Namely, it has been found a molecule having weak

or intermediate diradical character (~0.1 < y0 < ~0.5) together with quite weak tetraradical character (y1 < ~0.2y0) tends to satisfy the two conditions (i) and (ii).20,23

Indeed, on the

basis of this guideline, several candidates for SF have been proposed.21,22, 24,26

In the case of

2E(T1) – E(S1) < 0 with the large energy difference, SF is expected to be realized but the large difference |2E(T1) – E(S1)| leads to a large thermal energy loss.

Thus, this difference is 2

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required to be small for the photovoltaic cell application.

In this study, we aim to tune the

diradical character in polycyclic aromatic molecules, bisanthene derivatives, in order to satisfy these conditions (i) and (ii) with keeping the energy loss small.

Chart 1. Molecular structures of polycyclic aromatic hydrocarbons (a), and closed-shell and open-shell resonance structures of 1 (b), 2-X (c) and 3-X (d). In (b), (c) and (d), Clar's sextets are shown by bold solid lines.

We examine bisanthene 1 and its derivatives 2-X and 3-X shown in Chart 1.

Molecule

1 is known to have non-negligible diradical character by a theoretical calculation,30 whose 3 ACS Paragon Plus Environment


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intermediate value (y0 = 0.47) indicates that this is a candidate for SF based on our design guideline.

The open-shell singlet nature in 1 is intuitively understood from the resonance

structures20–24,26,30–32 shown in Chart 1.

Comparing the number of Clar's sextets32 in the

closed-shell and open-shell forms, a larger number of Clar's sextets in the open-shell form of 1 corresponds to its non-negligible open-shell singlet character.30

Unfortunately, its triplet

excited state energy E(T1) is, to our best knowledge, not reported from any experiments nor theoretical calculations.

Thus, we evaluate the excitation energies related to the energy level

matching conditions (i) and (ii), and diradical character of 1.

On the basis of the result, we

can determine the direction of change, whether we should enhance or reduce the diradical character, for efficient SF in the molecule by chemical modifications.

In this study, we

examine the effects of two types of modifications, that is, the attaching aromatic moieties and twisting the π-plane, on the diradical character.

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Table 1. Diradical Character (y0 and y1) and Excitation Energy (E(S1), E(T1) and E(T2)) in eVa Molecule

y0

y1

E(S1)

E(T1)

E(T2)

2E(T1) – E(S1)

2E(T1) – E(T2)

1

0.474

0.043

2.393

0.939

2.583

–0.516

–0.706

2-O

0.369

0.034

2.801

1.360

2.923

–0.081

–0.203

2-S

0.328

0.032

2.867

1.521

3.026

0.175

0.015

2-C2H2

0.201

0.072

3.421

2.205

3.147

0.989

1.263

3-F

0.396

0.040

2.520

1.258

2.716

–0.004

–0.200

3-Cl

0.397

0.046

2.468

1.298

2.631

0.127

–0.036

3-CH3

0.371

0.041

2.572

1.367

2.801

0.163

–0.066

a

Evaluated by the approximate spin-projected Hartree-Fock/cc-pVDZ method and the spin-flip TD-PBE50/cc-pVDZ method, respectively. The second highest excited triplet state energy is evaluated by the TDDFT method with the LC-BLYP functional and cc-pVDZ basis set using the triplet reference state obtained from spin-unrestricted Kohn-Sham equation. See the Supporting Information for detail.

The calculated diradical character and excitation energies of 1 are given in Table 1. The computational details are found in the Supporting Information.

As predicted in the

previous study30 and the resonance structures, 1 turns out to have intermediate diradical character, y0 = 0.474, and negligible tetraradical character, y1 = 0.043.

As seen from the

excitation energies of 1, the conditions (i) and (ii) are satisfied together with somewhat large energy loss of |2E(T1) – E(S1)| = 0.516 eV.

Therefore, 1 is expected to exhibit SF, while its

potential for OPV application might be reduced due to its thermal energy loss and, possibly, due to slow SF because of multiphonon relaxation.33

In order to reduce the loss, we examine

two kinds of chemical modifications below.



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Figure 1. Diradical character y0 (left) and excitation energy (right) for 1, 2-X (X = O, S, C2H2) and 3-X (X = F, Cl, CH3). The diradical character is evaluated by the approximate spin-projected Hartree-Fock/cc-pVDZ method. The excitation energies of the lowest triplet and singlet states are evaluated by the spin-flip TD-PBE50/cc-pVDZ method, respectively. The second highest excited triplet state energy is evaluated by the TDDFT method with the LC-BLYP functional and cc-pVDZ basis set using the triplet reference state obtained from spin-unrestricted Kohn-Sham equation. See the Supporting Information for detail.

First, we consider the resonance structures, which is known to be useful for clarifying the spatial nature of the diradical character and its relationship to aromatic nature of a molecule qualitatively.20–24,26,30–32

As seen from Chart 1, in 1, the number of Clar's sextets

increases from two in the closed-shell form to four in the diradical form.

This indicates that

if the number of Clar's sextets were increased in the closed-shell form by a chemical modification, the diradical character y0 would be reduced.

As an example, attaching

aromatic rings at the sides of 1 is one possible way to do that.34,35

Attaching benzene rings 6


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(2-C2H2, see Chart 1) increases the number of sextets from two in 1's closed-shell form to four in 2-C2H2's closed-shell form, while keeping that in the open-shell form of 2-C2H2.

It

is also known that the strength of aromaticity significantly differs for each aromatic ring and affects the diradical character.24,

36, 37

Attaching other aromatic rings, furan (2-O) and

thiophene (2-S), in the same way with that of 2-C2H2 is also considered. four Clar's sextets both in the closed-shell and open-shell forms.

These have also

The calculated diradical

character and excitation energy are presented in Table 1, and the relationship between the diradical character and excitation energy is also shown in Figure 1.

As expected from the

resonance structures, 2-C2H2, 2-S and 2-O, whose Clar's sextets are increased in their closed-shell forms, are found to have smaller y0 than of 1.

The diradical character y0 is

shown to decrease in the order 0.474 (1) > 0.369 (2-O) > 0.328 (2-S) > 0.201 (2-C2H2).

As

a result, these three substituted compounds show higher excitation energies E(S1) and E(T1) than those of unsubstituted compound 1, which makes them exothermic with a small energy loss (2-O), and endothermic with a small energy barrier (2-S) and with a large energy barrier (2-C2H2). Thus, 2-O is expected to be better SF material than 1 due to the smaller energy loss than that of 1.

The energy barrier in 2-S (2E(T1) – E(S1) = +0.175 eV) might not be a

matter because it is small like that in tetracene, which is known to be a good SF material with the small energy barrier 2E(T1) – E(S1) = +0.18 eV obtained from the experiment38 and +0.179 eV evaluated from the same level of calculation (see the Supporting Information). There have been no reports of efficient SF in a molecule with a very large energy barrier like +0.989 eV of 2-C2H2 except for the case with photo-activation.4

We note that the diradical

character y1 is not changed dramatically by these aromatic-ring attachments because this chemical modification does not increase the number of Clar's sextets in the open-shell form with tetraradical structure.21, 30

Hence, triplet-triplet annihilation is found to be endothermic



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for a compound (2-O) with a relatively low E(T1) but to be exothermic for others (2-S and 2-C2H2).21,24

Figure 2. 2D NICS(1)zz map for planar molecules 1 and 2-X evaluated by the LC-BLYP/cc-pVDZ method. Red (negative) and blue (positive) distributions indicate aromatic and anti-aromatic regions, respectively. See also the resonance structures in Chart 1.

The effect of aromatic-ring attachment on the diradical character can also be confirmed by evaluating the nuclear independent chemical shift 1 Å above the π-plane, NICS(1)zz.39,40 The 2D map of NICS(1)zz in Figure 2 clearly shows that the attached rings induce significant local aromaticity at the attached ring regions (negative values of NICS(1)zz) and enhance the local aromaticity in the middle biphenyl moiety relative to 1 with different strength depending on the aromaticity of the attached rings, or on their chemical species, furan, thiophene and benzene.

From the 2D NICS(1)zz map, we observe stronger aromaticity in the attached rings

of 2-C2H2 than that of 2-O and 2-S.

By comparing the resonance structure in Chart 1 and

the 2D NICS(1)zz map, the induced aromaticity in the attached rings and the enhancement of aromaticity in the middle biphenyl moiety represents the increase in the closed-shell character in 2-X as compared to 1.

Actually, as increasing the aromaticity of the attached rings, the

diradical character y0 becomes smaller, the feature of which corresponds to the increase of the contribution of the closed-shell form with a larger number of Clar's sextets in the resonance structures.


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Figure 3. Schematic diagram of molecular orbital interaction of 1 and 3-X (X = F, Cl, CH3) (a), and of 1 and 2-X (X = O, S, C2H2). The parent MOs, that is, the HOMO and LUMO of anthracene moieties, interact with each other and lead the H, H', L and L' in 1. The lone-pair orbitals in (a) are present only for X = F and Cl. The MO energy splittings, Δε(H–H') and Δε(L–L'), are reduced by chemical modifications in 2-X and 3-X relative to that in 1. Arrow colors correspond to the colors of bars in Figure 4.

The reduction of the diradical character y0 of 2-X as compared to that of 1 is also understood from the viewpoint of the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied MO (LUMO).21–24,30,31,36,37

A schematic view of 9



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the MO diagram for our model molecules is shown in Figure 3.

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As seen from Figure 3a, the

HOMO and the LUMO of 1 are the anti-bonding and bonding linear combinations of the "parent" HOMOs and LUMOs in two anthracene moieties, respectively.

By attaching

aromatic rings on 1, as seen from Figure 3b, the anti-bonding interaction in the LUMO and no interaction with lone-pair orbitals in oxygen and sulfur atoms in the HOMO increase the HOMO–LUMO energy gap for 2-X (X = O, S) as compared to that of 1 (see also Figure S2). In 2-C2H2, from Figure 3b, the anti-bonding interaction in the LUMO of 1 with the attached ethylene moieties raises the LUMO energy level of 2-C2H2, and the bonding interaction in the HOMO of 1 with the attached ethylene moieties lowers the HOMO energy level of 2-C2H2, resulting in the larger HOMO–LUMO energy gap as compared to those of 1 and 2-X (X = O, S).

The enhancement of the HOMO–LUMO energy gap in 2-X relative to that in 1

corresponds to the reduction of the diradical character of 2-X relative to that of 1.

In order

to confirm this consideration, we evaluate three orbital energy gaps, that is, the HOMO–LUMO energy gap (Δε(H–L) = ε(L) – ε(H)), HOMO-HOMO' energy gap (Δε(H–H') = ε(H) – ε(H')) and LUMO-LUMO' energy gap (Δε(L–L') = ε(L') – ε(L)), where ε(i) is the energy of the MO i, and the HOMO' and LUMO' are composed of the same parent MOs, the HOMO and LUMO of anthracene, respectively, with the opposite phases in the linear combinations (see Figure 3b).

As seen from Figure 4, the reduced diradical character y0 in

2-X corresponds to the enhanced HOMO–LUMO gap Δε(H–L), which is also related to the reduced parent MO energy splittings Δε(H–H') and Δε(L–L').

As predicted in the above

discussion, in 2-O and 2-S, orbital interaction between 1 and the attached rings in the LUMO is shown to reduce the Δε(L–L'), and hence to enhance Δε(H–L).

In 2-C2H2, due to the

orbital interaction between 1 and ethylene moieties both in the HOMO and LUMO, both Δε(H–H') and Δε(L–L') are shown to be reduced significantly, which is found to enhance


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Δε(H–L) and thus to reduce y0.

These observations are consistent with the above qualitative

consideration of orbital interaction diagram shown in Figure 3b.

1.0

4.0 Δε(H-L) -3 eV

y

Δε(H-H')

0.8

3.0

Δε(L-L')

0

Diradical character y [-]

0

0.6 2.0 0.4 1.0 0.2

0.0

1

2-O

2-S 2-C H 3-F 2

2

3-Cl 3-CH

Orbital energy gap [eV]

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0.0

3

Figure 4. Diradical character y0 (left) and MO energy splitting (right) evaluated by the approximate spin-projected Hatree-Fock/cc-pVDZ method and LC-BLYP/cc-pVDZ method, respectively. These energy splittings are shown in Figure 3.

Another possible way of chemical modification for reducing the diradical character y0 rather than attaching aromatic rings may be considered from another standpoint in the orbital diagram of 1, Figure 3a.

The parent MO energy splittings, Δε(H–H') and Δε(L–L'), are

considered to be related to the overlap between the pairs of parent MOs.

From this insight,

we expect that reducing the overlap between them could decrease the diradical character



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because the parent MO energy splittings are also related to Δε(H–L) and thus y0.

To achieve

this change, we substitute four hydrogen atoms in 1 at their sides by larger atoms, fluorine (3-F) and chlorine (3-Cl), and by an alkyl group, methyl group (3-CH3).

Methyl group

substitution at one side of 1 is known to reduce the excitation energy, where the diradical character change was not recognized.41

Such steric hinderance is expected to cause

non-planarity in π-conjugation, and thus to reduce the orbital overlap between the parent MOs. As predicted from the qualitative consideration of the MO interaction diagram, 3-X are shown to have smaller parent MO energy splittings Δε(H–H') and Δε(L–L') than those of 1 (see Figure 4), which corresponds to the larger HOMO–LUMO energy gaps Δε(H–L) in 3-X than that of 1. Note here that although the lone-pair orbitals of halogen atoms in 3-F and 3-Cl could interact with the HOMO and LUMO of 1, they hardly affect the HOMO–LUMO gap Δε(H–L) because they interact with both the HOMO and LUMO of 1 in anti-bonding fashion (see Figure 3a and Figure S3).

Thus, the change in orbital energy gaps in 3-X from that of 1

is mainly explained by the reduced overlap.

The diradical characters and the excitation

energies of 3-X are also evaluated and summarized in Table 1 and Figure 1.

As expected,

3-X are shown to have smaller diradical character y0 than that of 1, resulting in the relative increase in 2E(T1) with respect to E(S1), that is, –0.004 eV (3-F), 0.127 eV (3-Cl) and 0.163 eV (3-CH3).

3-F is approximately isoergic in SF and hence could be a promising SF

material with negligible energy loss. The energy barriers for SF in 3-Cl and 3-CH3 are again smaller than that of tetracene, so that they are still worth experimental investigation. In addition, in all 3-X, the second energy level requirement is achieved: 2E(T1) – E(T2) = –0.200 eV (3-F), –0.036 eV (3-Cl) and –0.066 eV (3-CH3).

This indicates low probability

of triplet-triplet annihilation in all 3-Xs. In this study, we have demonstrated a molecular design for efficient SF from the viewpoint of the energy level matching based on the diradical character tuning through


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aromatic-ring attachment on and twisting the π-plane of a polycyclic aromatic hydrocarbon, bisanthene 1, which is a singlet diradicaloid.

Although 1 has been shown to have slightly

excessive diradical character y0 for the application in SF, the present chemical modifications are found to appropriately reduce the diradical character, resulting in the better matching in the energy level except for 2-C2H2, where the diradical character is reduced too much.

The

designed molecules have been shown to have smaller energy loss for SF than that in 1, or to be approximately isoergic (3-F).

Although some molecules (2-S, 3-Cl, 3-CH3) are found to

be slightly endothermic, they are expected to overcome their energy barriers in a condensed phase like tetracene, which has the similar energy barrier to those of these compounds.

The

origin of these chemical modification effects has been clarified by examining the 2D NICS(1)zz maps and MO energy diagrams.

The present chemical modification approach

could be applied to other diradical molecules, especially for polycyclic aromatic hydrocarbons, which includes a large variety of promising candidates for SF compounds such as acenes. Namely, the present result vastly extends the search area of SF molecules and thus will pave the way to realizing the SF applications in the future photoelectric materials.

ASSOCIATED CONTENT Supporting Information Details of electronic structure calculation; frontier molecular orbitals; diradical characters and excitation energies of tetracene and pentacene.

This material is available free of charge via the

Internet at http://pubs.acs.org.

ACKNOWLEDGEMENTS This work is supported by JSPS KAKENHI Grant Number JPA2645050 in JSPS Research Fellowship for Young Scientists, Grant Number JP25248007 in Scientific Research (A),



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Grant Number JP24109002 in Scientific Research on Innovative Areas “Stimuli-Responsive Chemical Species”, Grant Number JP15H00999 in Scientific Research on Innovative Areas “π-System Figuration”, and Grant Number JP26107004 in Scientific Research on Innovative Areas “Photosynergetics”.


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References (1) Smith, M. B.; Michl, J. Singlet Fission. Chem. Rev. 2010, 110, 6891–6936. (2) Smith, M. B.; Michl, J. Recent Advances in Singlet Fission. Annu. Rev. Phys. Chem. 2013, 64, 361–386. (3) Hanna, M. C.; Nozik, A. J. Solar Conversion Efficiency of Photovoltaic and Photoelectrolysis Cells with Charge Multiplication Absorbers. J. Appl. Phys. 2006, 100, 074510/1–074510/8. (4) Singh, S.; Jones, W. J.; Siebrand, W.; Stoicheff, B. P.; Schneider, W. G. Laser Generation of Excitons and Fluorescence in Anthracene Crystals. J. Chem. Phys. 1965, 42, 330–342. (5) Liu, Y.; Chang, C.; Wang, R.; Chang, B.; Tan, Z.; Wang, X.; Xiao, M. Large Optical Nonlinearity by Singlet Fission in Pentacene Films. Angew. Chem. Int. Ed. 2015, 54, 1–6. (6) Burdett, J. J.; Bardeen, C. J. The Dynamics of Singlet Fission in Crystalline Tetracene and Covalent Analogs. Acc. Chem. Res. 2013, 46, 1312–1320. (7) Willson, M. W. B.; Rao, A.; Johnson, K.; Gélinas, S.; di Pietro, R.; Clark, J.; Friend, R. H. Temperature-Independent Singlet Exciton Fission in Tetracene. J. Am. Chem. Soc. 2013, 135, 16680−16688. (8) Yost, S. R.; Lee, J.; Wilson, M. W. B.; Wu, T.; McMahon, D. P.; Parkhurst, R. P.; Thompson, N. J.; Congreve, D. N.; Rao, A.; Johnson, K. et al. A Transferable Model for Singlet-fission Kinetics. Nature Chem. 2014, 6, 492–497. (9) Chan, W.-L.; Berkelbach, T. C.; Provorse, M. R.;

Monahan, N. R.; Tritsch, J. R.;

Hybertsen, M. S.; Reichman, D. R.; Gau, J.; Zhu, X.-Y. The Quantum Coherent Mechanism for Singlet Fission: Experiment and Theory. 2013, 46, 1321–1329. (10) Wilson, M. W. B.; Rao, A.; Clark, J.; Kumar, R. S. S.; Brida, D.; Cerullo, G.; Friend, R. H. Ultrafast Dynamics of Exciton Fission in Polycrystalline Pentacene. J. Am. Chem. Soc. 2011, 133, 11830–11833.



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(11) Zimmerman, P. M.; Musgrave, C. B.; Head-Gordon, M. A Correlated View of Singlet Fission. Acc. Chem. Res. 2013, 46, 1339–1347. (12) Walker, B. L.; Musser, A. J.; Beljonne, D.; Friend, R. H. Singlet Exciton Fission in Solution. Nature Chemistry 2013, 5, 1019–1024. (13) Zeng, T.; Hoffmann, R.; Ananth, N. The Low-Lying Electronic States of Pentacene and Their Roles in Singlet Fission. J. Am. Chem. Soc. 2014, 136, 5755−5764. (14) Berkelbach, T. C.; Hybertson, M. S.; Reichman, D. R. Microscopic Theory of Singlet Exciton Fission. III. Crystalline Pentacene. J. Chem. Phys. 2015, 141, 074705/1–074705/12. (15) Singlet Exciton Fission in Polycrystalline Thin Films of a Slip-Stacked Perylenediimide. Eaton, S. W.; Shoer, L. E.; Karlen, S. D.; Dyar, S. M.; Margulies, E. A.; Veldkamp, B. S.; Ramanan, C.; Hartzler, D. A.; Savikhin, S. Marks, T. J. et al. J. Am. Chem. Soc. 2013, 135, 14701−14712. (16) Nagarajan, K; Mallia, A. R.; Reddy, V. S.; Hariharan, M. Access to Triplet Excited State in Core-Twisted Perylenediimide. J. Phys. Chem. C, 2016, 120, pp 8443–8450. (17) Mirjani, F.; Renaud, N.; Gorczak, N.; Grozema, F. C. Theoretical Investigation of Singlet Fission in Molecular Dimers: The Role of Charge Transfer States and Quantum Interference. J. Phys. Chem. C 2014, 118, 14192−14199. (18) High Triplet Yield from Singlet Fission in a Thin Film of 1,3-Diphenylisobenzofuran. Johnson, J. C.; Nozik, A. J.; Michl, J. J. Am. Chem. Soc. 2010, 132, 16302–16303. (19) Mechanism of Singlet Fission in Thin Films of 1,3-Diphenylisobenzofuran. Schrauben, J. N.; Ryerson, J. L.; Michl, J.; Johnson, J. C. J. Am. Chem. Soc. 2014, 136, 7363−7373. (20) Minami, T.; Nakano, M. Diradical Character View of Singlet Fission. J. Phys. Chem. Lett. 2012, 3, 145−150. (21) Ito, S.; Minami, T.; Nakano, M. Diradical Character Based Design for Singlet Fission of Condensed-Ring Systems with 4nπ Electrons. J. Phys. Chem. C 2012, 116, 19729–19736.


Page 17 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Minami, T.; Ito, S.; Nakano, M. Theoretical Study of Singlet Fission in Oligorylenes. J. Phys. Chem. Lett. 2012, 3, 2719−2723. (23) Minami, T.; Ito, S.; Nakano, M. Fundamental of Diradical Character Based Molecular Design for Singlet Fission. J. Phys. Chem. Lett. 2013, 4, 2133–2137. (24) Ito, S.; Nakano, M. Theoretical Molecular Design of Heteroacenes for Singlet Fission: Tuning the Diradical Character by Modifying π-Conjugation Length and Aromaticity. J. Phys. Chem. C 2015, 119, 148−157. (25) Akdag, A.; Havlas, Z.; Michl, J. Search for a Small Chromophore with Efficient Singlet Fission: Biradicaloid Heterocycles. J. Am. Chem. Soc. 2012, 134, 14624−14631. (26) Zeng, T.; Ananth, N.; Hoffmann, R. Seeking Small Molecules for Singlet Fission: A Heteroatom Substitution Strategy. J. Am. Chem. Soc. 2014, 136, 12638−12647. (27) Wen. J.; Havlas, Z.; Michl, J. Captodatively Stabilized Biradicaloids as Chromophores for Singlet Fission. J. Am. Chem. Soc. 2015, 137, 165−172. (28) Yamaguchi, K. The Electronic Structures of Biradicals in the Unrestricted Hartree-Fock Approximation. Chem. Phys. Lett. 1975, 33, 330–335. (29) Yamaguchi, K. In Self-Consistent Field: Theory and Applications; Carbo, R., Klobukowski, M., Eds.; Elsevier: Amsterdam, The Netherlands, 1990; pp 727−828. (30) Nagai, H.; Nakano, M.; Yoneda, K.; Kishi, R.; Takahashi, H.; Simizu, A.; Kubo, T.; Kamada, K.; Ohta, K.; Botek, E. et al. Signature of Multiradical Character in Second Hyperpolarizabilities of Rectangular Graphene Nanoflakes. Chem. Phys. Lett. 2010, 489, 212–218. (31) Konishi, A.; Hirao, Y.; Matsumoto, K.; Kurata, H.; Kishi, R.: Shigeta, Y.; Nakano, M.; Tokunaga, K.; Kamda, K.; Kubo, T. Synthesis and Characterization of Quarteranthene: Elucidating the Characteristics of the Edge State of Graphene Nanoribbons at the Molecular Level. J. Am. Chem. Soc. 2013, 135, 1430–1437.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 28

(32) Clar, E. The Aromatic Sextet; Wiley: London, 1972. (33) Busby, E.; Berkelbach, T. C.; Kumer, B.; Chernikov, A.; Zhong, Y.; Hlaing, H.; Zhu, X.-Y.; Heinz, T.; Hybertson, M. S.; Sfeir, M. Y. et al. Multiphonon Relaxation Slows Singlet Fission in Crystalline Hexacene. J. Am. Chem. Soc. 2014, 136, 10654−10660. (34) Jiang, D.-e.; Dai, S. Circumacenes versus Periacenes: HOMO–LUMO Gap and Transition from Nonmagnetic to Magnetic Ground State with Size. Chem. Phys. Lett. 2008, 466, 72–75. (35) Konishi, A.; Hirao, Y.; Matsumoto, K.; Kurata, H.; Kubo, T. Facile Synthesis and Lateral π-Expansion of Bisanthenes. Chem. Lett. 2013, 42, 592–594. (36) Nakano, M.; Nakagawa, M.; Kishi, R.; Ohta, S.; Nate, M.; Takahashi, H.; Kubo, T.; Kamada, K.; Ohta, K.; Champagne, B. Second Hyperpolarizabilities of Singlet Polycyclic Diphenalenyl Radicals: Effects of the Nature of the Central Heterocyclic Ring and Substitution to Diphenalenyl Rings. J. Phys. Chem. A 2007, 111, 9102–9110. (37) Kishi, R.; Ochi, S.; Izumi, S.; Makino, A.; Nagami, T.; Fujiyoshi, J.-y.; Matsushita, N.; Saito, M.; Nakano, M. Diradical Character Tuning for the Third-Order Nonlinear Optical Properties of Quinoidal Oligothiophenes by Introducing Thiophene-S,S-dioxide Rings. Chem. Eur. J. 2016, 22, 1493–1500. (38) Tomkiewicz, Y.; Groff, R. P.; Avakian, P. Spectroscopic Approach to Energetics of Exciton Fission and Fusion in Tetracene Crystals. J. Chem. Phys. 1971, 54, 4504–4507. (39) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 2005, 105, 3842–3888. (40) Fallah-Bagher-Shaidaei, H.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Which NICS Aromaticity Index for Planar π Rings Is Best? Org. Lett. 2006, 8, 863–866.


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(41)


Brockmann,

H.;

Randebrock,

R.

Synthese

und

Absorptionsspektren

einiger

meso-Naphthodianthren-Derivate. Chem. Ber. 1951, 84, 533–545.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chart 1


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Figure 1



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2


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Figure 3



Figure 4

1.0

4.0 Δε(H-L) -3 eV

y

Δε(H-H')

0.8

3.0

Δε(L-L')

0

Diradical character y [-]

0

0.6 2.0 0.4 1.0 0.2

0.0

1

2-O

2-S 2-C H 3-F 2

2


3-Cl 3-CH

3

0.0

Orbital energy gap [eV]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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TOC

O

O

F

F

F

F

Diradical character y0 Energy loss |2E(T1) – E(S1)|

Isoergic Singlet Fission



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Figure S1


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Figure S2



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure S3


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Diradical Character-Based Design for Singlet Fission of Bisanthene

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