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

The photoexcited triplet state of dyes can generate highlypolarizedelectron spins for sensing and dynamic nuclear polarization. However,while triplets exhibit long spin-lattice relaxation times (T (1)) on the microsecond scale in solids, the polarizationquickly relaxes on the nanosecond scale in solution due to the rotationalmotion of chromophores. Here, we report that the immobilization ofdye molecules on a solid surface allows molecular contact with a liquidwhile maintaining high polarization and long T (1) as in a solid. By adsorbing anionic porphyrins on cationicmesoporous silica gel, porphyrin triplets exhibit high polarizationand long T (1) at the solid-liquidinterface of silica and toluene. Furthermore, porphyrin triplets onthe solid surface can exchange spin polarization with TEMPO radicalsin solution. This simple and versatile method using the solid-liquidinterface will open the door for utilizing the photoinduced tripletspin polarization in solution, which has been mainly limited to thesolid-state.

Automated summary

By immobilizing dye molecules on a solid surface, high polarization and long spin-lattice relaxation times can be maintained while allowing molecular contact with a liquid. Anionic porphyrins adsorbed on cationic mesoporous silica gel exhibit high polarization and long spin-lattice relaxation times at the solid-liquid interface. Additionally, 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 opens up possibilities for utilizing photoinduced triplet spin polarization in solution, which was previously mainly limited to the solid-state.