Photolysis of Labile Bonds Towards Radical Generation: Case Study of Alkylverdazyls

Abstract

Two series of stable verdazyl radical’s derivatives specifically 1,2,4,6-substituted-1,4-dihydro-1,2,4,5-tetrazin-3(2H)-ones (also called “alkylverdazyls” or “AlkVZs”) were systematically investigated in photoactivated C-N bond homolysis. The in-depth evaluation of processes evidenced several factors played the pivotal role in the generation of radicals during photon absorption. According to quantum chemical calculations, the generation of charge-separated excited state where one electron locates at the verdazyl and the second one distributed at the alkyl part is the most influenced factor. The theoretical approach also allows predicting reaction rate constant based on oscillator strengths of S0→S1 transition in AlkVZs. Surprisingly, photon density of LED source has no less weight in controlling of reaction efficiency and decreasing of light power could lower the yield of radicals for two times with remaining of full conversion of starting materials. Our results open the perspectives for achieving of high yields in photochemical transformations not only by variation of wavelength of light but also via careful design of molecular structure and changing of LED power.