Fig. 3. (a) One-dimensional natural abundance ²⁹Si DNP-SENS CP-CPMG spectrum of I, recorded at 18.8 T (800 MHz) and 40 kHz MAS at a sample temperature of ∼115 K. The sample was impregnated with a solution of 10 mM AMUpol in 90 : 10 D₂O/H₂O, and transferred into a 1.3 mm rotor. During acquisition, SPINAL-64 decoupling²² was applied with a rf amplitude of 130 kHz. The cross-polarization (CP) contact time was 3 ms and the number of scans was 256 (total acquisition time 17 minutes). The CP-CPMG spectrum is shown in its echo reconstructed form and was obtained by adding up the whole echoes of the FIDs in the time domain, followed by Fourier transform and application of a first-order phase correction. A total of 60 echoes were acquired. Up to 120 echoes could be acquired (Fig. S13, ESI†). (b) Contour plot of a two-dimensional ¹H–¹³C spectrum of I recorded with DNP at 18.8 T (800 MHz) and 40 kHz MAS. A total of 38 t ₁ increments of 40 μs with 256 scans each were recorded. The CP contact time was 700 μs, and the polarization-buildup interval was 4 s. The total experimental time was 10.8 hours. SPINAL-64 heteronuclear decoupling was applied during t ₂ with an rf amplitude of 100 kHz. During t ₁, eDUMBO-1₂₂ ²³ homonuclear decoupling was applied with an rf amplitude of 150 kHz. A scaling factor of 0.56 was applied to correct the ¹H chemical shift scale.