Generation and Transfer of Triplet Electron Spin Polarization at Solid-Liquid Interface

Abstract

The photoexcited triplet state of dyes can generate highly polarized electron spins for sensing and dynamic nuclear polarization. However, while triplets exhibit long spin-lattice relaxation times (T1) on the microsecond scale in solids, the polarization quickly relaxes on the nanosecond scale in solution due to the rotational motion of chromophores. Here, we report that the immobilization of dye molecules on a solid surface allows molecular contact with a liquid while maintaining high polarization and long T1 as in a solid. By adsorbing anionic porphyrins on cationic mesoporous silica gel, porphyrin triplets exhibit high polarization and long T1 at the solid-liquid interface of silica and toluene. Furthermore, porphyrin triplets on the solid surface can exchange spin polarization with TEMPO radicals in solution. This simple and versatile method using the solid-liquid interface will open the way for utilizing the photo-induced triplet spin polarization in solution, which has been mainly limited to the solid-state.

Protein–Ligand Interaction Analyses with Nuclear Magnetic Resonance Spectroscopy Enhanced by Dissolution Triplet Dynamic Nuclear Polarization

“…Dissolution DNP using triplet DNP is still a method in the development stage regarding the range of applicable molecules and the achievable polarization compared to the typical dissolution DNP using a cryogenic environment. Several methods are being developed toward obtaining high polarization for a variety of molecules using photoexcited triplet electrons, such as the polarization transfer using the intermolecular NOE, 20 the polarization transfer using nanocrystals, 21 the development of new polarizing agents with solution solubility, 34,35 the transfer of the triplet electron polarization to radicals in solution, 36 the use of singlet fission, 37 and the use of magnetically oriented microcrystal arrays. 38 The 13 C-based room temperature D-DNP NMR methods demonstrated in this study would strongly and directly contribute to the development of hypersensitive pharmaceutical experimental technology that would enable the screening of new drug compounds.…”