1H and 15N dynamic nuclear polarization studies of carbazole

N-15 NMR experiments, combined with dynamic nuclear polarization (DNP), are reported on carbazole doped with the stable free radical 1,3 bisdiphenylene-2-phenylallyl (BDPA). Doping shortens the nuclear relaxation times and provides paramagnetic centers that can be used to enhance the nuclear signal by means of DNP so that N-15 NMR experiments can be done in minutes. The factors were measured in a 1.4 T external field, using both unlabeled and 98% N-15 labeled carbazole with doping levels varying between 0.65 and 5.0 wt % BDPA. A doping level of approximately 1 wt % produced optimal results. DNP enhancement factors of 35 and 930 were obtained for H-1 and N-15, respectively making it possible to perform N-15 DNP NMR experiments at the natural abundance level.