Sebastian Kopp, Shunta Nakamura, Brian Phelan, Yong-Rui Poh, Samuel Tyndall, Paige Brown, Yuheng Huang, Joel Yuen-Zhou, Matthew Krzyaniak and Michael Wasielewski : Luminescent Organic Triplet Diradicals as Optically Addressable Molecular Qubits, Journal of the American Chemical Society, Vol.146, No.40, 27935-27945, 2024.
(Summary)
Optical-spin interfaces that enable the photoinitialization, coherent microwave manipulation, and optical read-out of ground state spins have been studied extensively in solid-state defects such as diamond nitrogen vacancy (NV) centers and are promising for quantum information science applications. Molecular quantum bits (qubits) offer many advantages over solid-state spin centers through synthetic control of their optical and spin properties and their scalability into well-defined multiqubit arrays. In this work, we report an optical-spin interface in an organic molecular qubit consisting of two luminescent tris(2,4,6-trichlorophenyl)methyl (TTM) radicals connected via the -positions of a phenyl linker. The triplet ground state of this system can be photoinitialized in its | state by shelving triplet populations as singlets through spin-selective excited-state intersystem crossing with 80% selectivity from | and | . The fluorescence intensity in the triplet manifold is determined by the ground-state polarization, and we show successful optical read-out of the ground-state spin following microwave manipulations by fluorescence-detected magnetic resonance spectroscopy. At 85 K, the lifetime of the polarized ground state is 45 ± 3 μs, and the ground state phase memory time is = 5.9 ± 0.1 μs, which increases to 26.8 ± 1.6 μs at 5 K. These results show that luminescent diradicals with triplet ground states can serve as optically addressable molecular qubits with long spin coherence times, which marks an important step toward the rational design of spin-optical interfaces in organic materials.
Paige Brown, Malik Williams, Shunta Nakamura, Jonathan Palmer, Ryan Young and Michael Wasielewski : Singlet Fission in Terrylene Monoimide Single Crystals and Polycrystalline Films: Influence of an Intramolecular Charge Transfer State, The Journal of Physical Chemistry C, Vol.128, No.1, 58-66, 2024.
Tomokazu Kinoshita, Shunta Nakamura, Makoto Harada, Taku Hasobe and Gaku Fukuhara : Control of intramolecular singlet fission in a pentacene dimer by hydrostatic pressure, Chemical Science, Vol.14, No.12, 3293-3301, 2023.
(Summary)
Singlet fission (SF), which produces two triplet excitons from a singlet exciton, has been identified as a novel nanointerface for efficient (photo)energy conversion. This study aims to control exciton formation in a pentacene dimer through intramolecular SF using hydrostatic pressure as an external stimulus. We reveal the hydrostatic-pressure-induced formation and dissociation processes of correlated triplet pairs (TT) in SF by means of pressure-dependent UV/vis and fluorescence spectrometry and fluorescence lifetime and nanosecond transient absorption measurements. The photophysical properties obtained under hydrostatic pressure suggested distinct acceleration of the SF dynamics by microenvironmental desolvation, the volumetric compaction of the TT intermediate based on solvent reorientation toward an individual triplet (T), and pressure-induced shortening of T lifetimes. This study provides a new perspective on the control of SF by hydrostatic pressure as an attractive alternative to the conventional control strategy for SF-based materials.
Shunta Nakamura, Hayato Sakai, Masaaki Fuki, Rikuto Ooie, Fumitaka Ishiwari, Akinori Saeki, Nikolai Tkachenko, Yasuhiro Kobori and Taku Hasobe : Thermodynamic Control of Intramolecular Singlet Fission and Exciton Transport in Linear Tetracene Oligomers, Angewandte Chemie International Edition, Vol.62, No.8, e202217704, 2023.
(Summary)
We newly synthesized a series of homo- and hetero-tetracene (Tc) oligomers to propose a molecular design strategy for the efficient exciton transport in linear oligomers by promoting correlated triplet pair (TT) dissociation and controlling sequential exciton trapping process of individual doubled triplet excitons (T+T) by intramolecular singlet fission. First, entropic gain effects on the number of Tc units are examined by comparing Tc-homo-oligomers [(Tc) : n=2, 4, 6]. Then, a comparison of (Tc) and Tc-hetero-oligomer [TcF -(Tc) -TcF ] reveals the vibronic coupling effect for entropic gain. Observed entropic effects on the T+T formation indicated that the exciton migration is rationalized by number of possible TT states increased both by increasing the number of Tc units and by the vibronic levels at the terminal TcF units. Finally, we successfully observed high-yield exciton trapping process (trapped triplet yield: Φ =176 %).
Shunta Nakamura, Hayato Sakai, Hiroki Nagashima, Masaaki Fuki, Kakeru Onishi, Ramsha Khan, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : Synergetic Role of Conformational Flexibility and Electronic Coupling for Quantitative Intramolecular Singlet Fission, The Journal of Physical Chemistry C, Vol.125, No.33, 18287-18296, 2021.
Shunta Nakamura, Hayato Sakai, Masaaki Fuki, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : EnthalpyEntropy Compensation Effect for Triplet Pair Dissociation of Intramolecular Singlet Fission in Phenylene Spacer-Bridged Hexacene Dimers, The Journal of Physical Chemistry Letters, Vol.12, No.28, 6457-6463, 2021.
(Summary)
Hexacene (Hc) is highly promising for singlet fission (SF). However, the number of SFs in Hc is extremely limited. As far as Hc dimers in solution are concerned, there is no report on the observation of the dissociation process from a correlated triplet pair (TT) to an individual one. The emphasis in this study is on the first observation of the quantitative TT generation together with the orientation-dependent photophysical discussions for TT dissociation using - and -phenyl-bridged Hc dimers. Moreover, the activation enthalpies of Hc dimers in TT dissociation are smaller than those of pentacene (Pc) dimers, whereas the relative entropic contributions for Gibbs free energy of activation are much larger than the enthalpic ones in both Hc and Pc dimers. This implies that the vibrational motions are responsible for the intramolecular conformation changes associated with the TT dissociation. Consequently, "enthalpy-entropy compensation" has a large impact on the rate constants and quantum yields.
Yasuhiro Kobori, Masaaki Fuki, Shunta Nakamura and Taku Hasobe : Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate TripletTriplet Dissociations via the Intramolecular Singlet Fissions, The Journal of Physical Chemistry B, Vol.124, No.42, 9411-9419, 2020.
(Summary)
Importance of vibronic effects has been highlighted for the singlet-fission (SF) that converts one high-energy singlet exciton into doubled triplet excitons, as strongly coupled multiexcitons. However, molecular mechanisms of spin conversion processes and ultimate decouplings in the multiexcitons are poorly understood. We have analyzed geometries and exchange couplings (singlet-quintet energy gaps: 6) of the photoinduced multiexcitons in the pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as -(Pc) and -(Pc)] by simulations of the time-resolved electron paramagnetic resonance spectra. We clarified that terahertz molecular conformation dynamics play roles on the spin conversion from the singlet strongly coupled multiexcitons (TT) to the quintet multiexcitons (TT) and on the intramolecular decouplings in the 6 to form spin correlated triplet pairs (T+T). The strongly coupled (TT) multiexcitons are revealed to possess entirely planar conformations stabilized by mutually delocalized spin distributions, while the intramolecular decoupled spin-correlated triplet pairs generated at 1 μs are also stabilized by distorted conformations resulting in two separately localized biradical characters.
Hayato Sakai, Ryutaro Inaya, Hiroki Nagashima, Shunta Nakamura, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : Multiexciton Dynamics Depending on Intramolecular Orientations in Pentacene Dimers: Recombination and Dissociation of Correlated Triplet Pairs, The Journal of Physical Chemistry Letters, Vol.9, No.12, 3354-3360, 2018.
(Summary)
Pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as o-(Pc) and m-(Pc)] were synthesized to examine intramolecular orientation-dependent multiexciton dynamics, especially focusing on singlet fission (SF) and recombination from correlated triplet pairs [(TT)]. Absorption and electrochemical measurements indicated strong intramolecular couplings of o-(Pc) relative to m-(Pc). Femtosecond and nanosecond TA measurements successfully demonstrated efficient SF in both dimers. In contrast, the dissociation process from the (TT) to the individual triplets [(2 × T)] was clearly observed in m-(Pc), which is in sharp contrast to a major recombination process in o-(Pc). Time-resolved electron spin resonance (TR-ESR) measurements demonstrated that the recombination and dissociation proceed from the quintet state of (TT) in m-(Pc). The rate constant of the SF was 2 orders of magnitude greater in o-(Pc) than that in m-(Pc) and was rationalized by enhanced electronic coupling between adjacent HOMOs of the Pc units.
Taku Hasobe, Shunta Nakamura, Nikolai Tkachenko and Yasuhiro Kobori : Molecular Design Strategy for High-Yield and Long-Lived Individual Doubled Triplet Excitons through Intramolecular Singlet Fission, ACS Energy Letters, Vol.7, No.1, 390-400, Dec. 2021.
Shunta Nakamura, Hayato Sakai and Taku Hasobe : Control of intramolecular singlet fission and subsequent two-electron transfer in tetracene dimers, Pacifichem 2021, Dec. 2021.
2.
Taku Hasobe, Shunta Nakamura and Hayato Sakai : High-Yield Singlet Fission of Acene-Based Molecular Assemblies for Sequential Photoinduced Process, 7th International Symposium on π-System Figuration, Osaka, Mar. 2019.
Proceeding of Domestic Conference:
1.
Shunta Nakamura, Hayato Sakai, Masaaki Fuki, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : 分子内一重項分裂の三重項対開裂過程におけるエンタルピーエントロピー補償効果, 2021年光化学討論会, Sep. 2021.
2.
Shunta Nakamura, Hayato Sakai, Masaaki Fuki, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : Singlet Fission in Tetracene Dimers and Oligomers, 日本化学会第101春季年会, Mar. 2021.
3.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : テトラセン分子ワイヤにおける一重項分裂の発現, 2020年光化学討論会, Sep. 2020.
4.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : Tetracene Molecular Wires for Efficient Singlet Fission, 日本化学会第100春季年会, Mar. 2020.
5.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : Synthesis and photophysical properties of covalently linked tetracene oligomers, 2019年光化学討論会, Sep. 2019.
6.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : 共有結合で連結したヘキサセン二量体の合成と一重項分裂の観測, 2019年光化学討論会, Sep. 2019.
7.
Shunta Nakamura, Hayato Sakai, Hiroki Nagashima, Yasuhiro Kobori, Nikolai Tkachenko and Taku Hasobe : Observation of Quantitative Intermolecular Two-Electron Transfer Process through Highly Efficient Singlet Fission in Tetracene Dimer, 日本化学会第99春季年会, Mar. 2019.
8.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : アセン二量体の高効率一重項分裂と逐次反応の発現, 第5回π造形科学若手研究会, Oct. 2018.
9.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : 新規ヘキサセン二量体の合成と高効率な一重項分裂の発現, 第29回基礎有機化学討論会, Sep. 2018.
10.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : 光機能性ヘキサセン誘導体の合成と分光特性, 日本化学会第98春季年会, Mar. 2018.
11.
Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : テトラセン二量体の一重項分裂発現と三重項励起状態の長寿命化, 第4回π造形科学若手研究会, Dec. 2017.
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Shunta Nakamura, Hayato Sakai, Nikolai Tkachenko and Taku Hasobe : テトラセン二量体のSinglet Fissionにおける配向とTriplet Pairの相関, 2017年光化学討論会, Sep. 2017.
13.
Shunta Nakamura, Hayato Sakai, Yasuyuki Araki, Takehiko Wada, Nikolai Tkachenko and Taku Hasobe : 均一溶液中におけるテトラセン二量体の一重項分裂発現, 日本化学会第97春季年会, Mar. 2017.