Properties of the short-lived triplet states of pyridazine and 3,6-dichloropyridazine studied by a time-resolved EPR method

Publisher Website
Google Scholar
Abstract
The magnetic and decay properties of the short‐lived triplet (T1) states of pyridazine and 3,6‐dichloropyridazine (DCP) were studied by means of time‐resolved EPR with laser excitation. The zfs of DCP in the p‐dibromobenzene (DBB) host are X=0.094 cm−1, Y=−0.164 cm−1, and Z=0.070 cm−1, and the nitrogen hfcc are Ax=27 G, Ay=18 G, and Az=25 G, which confirms the nπ* character of the T1 state. Similar zfs were obtained for DCP and pyridazine in other environments. The sublevel decay rate constants and the relative populating rates were determined from the analysis of the transient EPR signals measured at 3.0 K where the effect of the spin lattice relaxation can be neglected. It was found in both systems that ky is much greater than kx, kz as predicted by a simple group theoretical consideration. ky of DCP and pyridazine were determined to be on the order of 106 s−1, being larger than that of pyrimidine by a factor of ∼104. The reasons for the large ky are discussed, particularly, in terms of the distorted potential of the T1 state.