Kinetic investigation of thermal and photoinduced homolysis of alkylated verdazyls

The on-demand generation of stable organic radicals from the precursors can be considered as an essential challenge for the plethora of applications in various fields of science. In this contribution, we prepared a range ofN-(methyl)benzyl derivatives of 6-oxoverdazylviaatom transfer radical addition from moderate to high yields and studied their thermal- and photo-initiated homolysis. The kinetics of homolysis was measured, and the dissociating rate constantk(d), activation energyE(a)and frequency factorAwere estimated. Variation of the substituent at the C3-position of the verdazyl ring was successfully applied for fine-tuning the homolysis rate: the value ofk(d)was higher for alkylverdazyls with electron-withdrawing groups,e.g., theparanitro group afforded a 6-fold increase ink(d). In contrast to thermal homolysis, the rate of photoinduced decomposition depends on both the extinction coefficient and the value of activation energy. Thus, nitro-containing alkylated verdazyls show the highest homolysis rate in both types of initiations. The achieved results afford a novel opportunity in the controlled generation of verdazyls and further application of these compounds in medicine and chemical industry.