Time-domain observation of external magnetic field effects on the delayed fluorescence of N,N,N′,N′-tetramethyl-1,4-phenylenediamine in alcoholic solution

The external magnetic field effects (MFEs) on the intensity of the delayed fluorescence from N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD) are studied in mixed alcohol and 2-propanol under the conditions of both low and high concentration of TMPD at room temperature, In mixed alcohol solution, three different MFEs on the delayed fluorescence intensity are separated by time-domain observation and different concentration conditions. The MFEs in the solution of low concentration can be explained by the radical-pair mechanism (RPM) of the: TMPD cation radical and the solvated electron in the early-time region and the triplet-triplet pair mechanism (TTPM) through triplet-triplet annihilation (T-T annihilation) in the later-time region. In the solution of high concentration, the MFEs can be explained by the TTPM in the early-time region and the triplet-doublet pair mechanism (TDPM) in the later-time region. This TDPM affects the delayed fluorescence intensity of T-T annihilation. In 2-propanol, similar results are obtained, except for no apparent observation of the RPM. According to the present results, it is clarified that TMPD in alcohol emits two types of the delayed fluorescence, recombination type and T-T annihilation type. The former Shows the MFEs due to the RPM, and the latter shows the two different MFEs of the TTPM and the TDPM.