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Thursday, March 30, 2023

Singlet fission as a polarized spin generator for dynamic nuclear polarization

Singlet fission (SF), which kinds two triplet excitons from one single singlet exciton, has been extensively investigated for purposes in optoelectronics. SF can be recognized to generate spin-polarized quintet states in natural molecular techniques, which has been utilized for elucidating the mechanism of SF. Nonetheless, purposes utilizing spin levels of freedom in SF haven’t been achieved. Our group has managed the discrete meeting of pentacene spinoff in aqueous media by supramolecular complexation with cyclodextrins (CD) to trigger SF. As well as, we’ve enhanced 1H NMR sign depth of water molecules by transferring the spin polarization of the SF-derived quintet state to the 1H nuclear spins of the water molecule utilizing dynamic nuclear polarization (DNP) (Determine 1).

Determine 1. Schematic illustration of DNP utilizing SF-born quintet electron polarization. (A) Nuclear spins within the thermal equilibrium state. (B) Polarization switch from electron spins within the quintet state to 1H spins of water molecules.

The current examine is interdisciplinary, bridging the completely different fields of SF and DNP, which was impressed by our group’s earlier works within the two fields of triplet-triplet annihilation-based photon upconversion (TTA-UC) and DNP utilizing triplets1. In our TTA-UC research, we’ve been controlling triplet technology and diffusion primarily based on the management of chromophore meeting construction. Since SF is the reverse technique of TTA-UC and they’re intently associated, our group has lately been lively within the examine of SF. Alternatively, our group has additionally centered on the spin levels of freedom of triplets and their software to DNP to extend the sensitivity of NMR/MRI measurements of biomolecules. Since our group has been exploring completely different analysis themes with triplets as a standard key phrase, it was pure for us to merge them. As well as, this examine introduced collectively the synthesis, ESR, and DNP measurements of our group with the ultrafast spectroscopy of Miyata’s group, MD simulations of Watanabe’s group, and ESR simulations of Kobori’s group, and was made potential by this glorious collaborative analysis group.

It is very important enhance the NMR sensitivity of water molecules due to its potential software in protein NMR and MRI analysis. Triplet-DNP makes use of acene molecules equivalent to pentacene as a polarizing agent, but it surely has been a serious problem easy methods to switch the triplet electron spin polarization of the hydrophobic acenes to water. Our group has up to now succeeded in hyperpolarization of water molecules by dispersing polarizing brokers in water utilizing varied approaches equivalent to dispersion of nanoparticles in water1, 2 and ion pairing formation with cumbersome hydrophilic counterions3. In such a context, we combined cyclodextrin (CD) and water-soluble pentacene spinoff, NaPDBA4, and managed the aggregation state of pentacene chromophores by altering the internal diameter of CD. Naked NaPDBA and NaPDBA-γCD shaped pentacene dimers and confirmed SF in aqueous media (Determine 2).

Determine 2. Supramolecular meeting of NaPDBA. (A) Molecular buildings of NaPDBA and γ-CD and supramolecular meeting of solely NaPDBA and the NaPDBA-γCD inclusion advanced. (B) Absorption spectra of NaPDBA in water-glycerol at 143 Okay (black), NaPDBA-γCD in water-glycerol (1:1) at 143 Okay (blue), and NaPDBA in methanol at room temperature (purple).

DNP experiments had been carried out by dispersing the pentacene aggregates into water-glycerol glass to switch the electron spin polarization of the quintet state to the 1H nuclear spins of the water molecules. Because of this, we succeeded in enhancing the NMR sensitivity of water by an element of 20 (Determine 3). Because the Rabi frequency of the quintet spin state is greater than that of the triplet, we additionally demonstrated that polarization switch will be achieved by a weaker microwave energy with quintets than the standard DNP with triplets.

Determine 3. DNP utilizing SF-born quintet electron spin polarization. (a) 1H-NMR alerts underneath thermal situations and after quintet-DNP. (B) Microwave energy dependence of DNP enhancement.

This analysis pioneered SF as a polarized spin generator for quantum biotechnology. The improved NMR sensitivity of water molecules will be utilized to the structural evaluation of proteins and in vivo imaging with MRI. We imagine that ‘quintet-DNP’ is especially efficient for bettering NMR sensitivity in biology-relevant situations since it may well switch spin polarization with a weaker microwave energy.



1          https://websites.google.com/view/nobuhiroyanai/analysis

2          Nishimura, Okay. et al. Triplet dynamic nuclear polarization of nanocrystals dispersed in water at room temperature. Phys. Chem. Chem. Phys. 21, 16408-16412, doi:10.1039/c9cp03330k (2019).

3          Kouno, H. et al. Triplet dynamic nuclear polarization of crystalline ice utilizing water-soluble polarizing brokers. Chem. Commun. 56, 3717-3720, doi:10.1039/d0cc00836b (2020).

4          Matsumoto, N. et al. Proton Hyperpolarization Relay from Nanocrystals to Liquid Water. J. Am. Chem. Soc. 144, 18023-18029, doi:10.1021/jacs.2c07518 (2022).

5          Fujiwara, S. et al. Dynamic Nuclear Polarization of Steel-Natural Frameworks Utilizing Photoexcited Triplet Electrons. J. Am. Chem. Soc. 140, 15606-15610, doi:10.1021/jacs.8b10121 (2018).

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