The Chemically Induced Dynamic Electron Polarization (CIDEP) mechanisms in the hydrogen abstraction reactions of excited azaaromatic compounds; quinoxaline, phenazine, and quinoline are investigated in detail. It is shown that several polarization mechanisms are involved and the observed CIDEP spectra vary strongly depending on various factors such as the concentration, the temperature, the delay time, and the excitation light intensity. The net emissive spin polarization is ascribed mainly to the radical-triplet pair mechanism (RTPM), which is strongly dependent on the concentrations of the radical and triplet molecules. It is shown that the triplet molecules are long-lived and the condition to produce the RTPM polarization is satisfied. The observed time evolutions of the transient EPR signals are qualitatively explained on the basis of the rate equations, which include the RTPM polarization and the relaxation.