Fig. 1.

Pentacene doped in a p-terphenyl crystal and pulse sequence for DNP. (A) Energy diagram of pentacene doped in a p-terphenyl crystal. An electron excited with laser irradiation transits to a triplet state by intersystem crossing (ISC) and decays to the lowest triplet state. In a magnetic field of 0.40 T applied in parallel along the long molecular axis of pentacene, the energy gap between $|0\rangle$ and $|-1\rangle$ is ∼12 GHz, and the populations of the triplet sublevels are 12%, 76%, and 12%, respectively (17). The triplet state decays in 10–100 μs (18). (B) Pulse sequence for DNP and NMR detection. (C) Pentacene and p-terphenyl-2′,3′,5′,6′-$d_4$.