Thermal and oxidative syntheses, structure, and optical properties of 2,6,8-trisubstituted 1,2,3-triazolo[4,5:3,4]pyrazolo[1,5-a] pyrimidin-2-ium-1(3)-ides

This study reports the unexpected synthesis of eight examples of a new heterocyclic system, which is composed of a charged triazole ring fused to the pyrazolo[1,5-a]pyrimidine, named 2,8-(diaryl)-6-(trifluoromethyl)-[1,2,3] triazolo[4 & PRIME;,5 & PRIME;:3,4]pyrazolo[1,5-a]pyrimidin-2-ium-1(3)-ides (2). Compounds 2 were successfully synthesized from the reactions of E-3-(aryldiazenyl)-7-(trifluoromethyl)-pyrazolo[1,5-a]pyrimidin-2-amines (1) in yields of up to 85% by employing two different method: thermal azide decomposition and oxidative cyclization. In general, derivatives 2a-h presented absorption bands at the ultraviolet region (250-380 nm) and green emission properties with large Stokes shifts. Moreover, TD-DFT calculations were performed, and redox analysis was conducted by cyclic voltammetry.