Viscosity effects on optically generated electron and nuclear spin hyperpolarization

Abstract

Optically-generated dynamic nuclear polarization is increased in viscous mixtures due to longer lived electron spin polarization.

Dynamic Electron Polarization Lasting More Than 10 μs by Hybridizing Porphyrin and TEMPO with Flexible Linkers

“…This suggests that controlling the dynamics as well as the distance between the dye and the radical is important for both efficient DEP and long-lasting DEP. Based on the findings obtained in this study, we expect that the optimization of various dyes and radicals linked by flexible linkers will lead to the application of large and sustained DEP to ESR imaging and light-driven DNP. − …”

“…In addition, the ESR signal in the unlinked systems decayed within a few microseconds, whereas the ESR signal in the hybridized systems was observed for more than 10 μs. It has been reported that the integrated ESR signal over time is a good indicator of optically generated DNP, and hybridized systems are expected to show much better DNP performance than unlinked systems.…”

“…As a promising mechanism to achieve high electron spin polarization, dynamic electron polarization (DEP) via quenching of photoexcited states by stable radicals has been developed. − In particular, its application to DNP has the potential to break the intrinsic limit of the enhancement factor with radical electron spins in thermal equilibrium because it can generate large electron spin polarization even in low magnetic fields and at room temperature. This promise is becoming reality with the observation of Overhauser DNP driven by light irradiation without the microwave irradiation. − It was found that not only DEP efficiency but also long-lasting DEP are key factors toward efficient DNP …”

“…30−35 It was found that not only DEP efficiency but also long-lasting DEP are key factors toward efficient DNP. 32 The simplest system for inducing DEP is a solution of "unlinked" dyes and radicals. 8−29 However, since the encounter between the photoexcited species and the radicals is the rate-limiting step, intense laser irradiation and high concentration of dyes and radicals are necessary to obtain large DEP.…”

“…An alternative approach to facilitate this encounter is the "hybridized" system, where dyes and radicals are connected by covalent or noncovalent bonds. 34−56 This is promising for photodriven DNP [30][31][32][33][34][35]57 and EPR imaging. 58 The derivatives of quinones, 35−37 polyaromatics, 38−41 fullerene, 34,42 BODI-PY, 43 porphyrins, 44−52 and phthalocyanine 53−56 have been used as the chromophores for these hybridized systems.…”