Solid Effect Dynamic Nuclear Polarization Enhancement of >500 at 9.4 T

Efficient polarizing agents for dynamic nuclear polarization (DNP) enhanced magic angle spinning (MAS) NMR spectroscopy is of high current interest due the potential to significantly boost NMR sensitivity. While most efforts have centered on cross-effect (CE) or Overhauser effect (OE) mechanisms, yielding enhancements factors up to ~300 at 9.4 T, radicals yielding solid effect (SE) DNP have seen less development. Here we model the comparative performance of OE and SE mechanisms, and then measure 1H enhancement factors up to 500 from 1,3-bisdiphenylene-2-phenylallyl (BDPA) in an ortho-terphenyl (OTP) matrix at 9.4 T, 100 K, achieved via increased microwave power across the sample volume. The measured SE and OE performance is in good agreement with the predictions. We note that both the experimental and theoretical analyses indicate SE DNP remains saturation limited, particularly at elevated temperatures, and envisage that further improvements in microwave power will further increase SE DNP enhancement factors.