5‐Amino‐3‐methyl‐4‐phenylazo‐1H‐pyrazole and ethyl cyanoacetate reacted in solvent‐free media at 150°C to produce 7‐amino‐3‐phenylazo‐2‐methyl‐4H‐pyrazolo[1,5‐a]pyrimidine‐5‐one (3). A series of aromatic amines was coupled using this compound (3) and nitrous acid to produce new pyrazolo[1,5‐a] pyrimidine derivatives with two arylazo groups 4(a‐m). The structures of these dyes were determined via UV–vis, Fourier transform infrared, proton nuclear magnetic resonance, high‐resolution mass spectral data, and elemental analysis. After synthesis, the solvent and acid–base effects of the dyes were investigated within the UV–vis region. The antimicrobial properties of the dyes were also studied. All dyes exhibited activity against Gram‐positive and Gram‐negative bacteria, and even against fungi. The results were compared to conventional reference results from the antibiotics ciprofloxacin and ketoconazole. Antioxidant potentials were analyzed using in vitro antioxidant models on the basis of DPPH (1,1‐diphenyl‐2‐picrylhydrazyl) radical scavenging activities. Most of the compounds exhibited excellent antioxidant activities. In particular, compound 4b had a higher activity than Vitamin C.

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Ten novel fluorescent azo disperse dyes 2a–e (open forms) and 3a–e (closed forms) were obtained by the coupling reaction of carbocyclic amine based diazonium chloride with compounds 2 and 3. The synthesized dyes were characterized by elemental analysis, high‐resolution mass spectrometry, Fourier transform infrared, and NMR spectral techniques. Moreover, we investigated the substituent effect and solvatochromic properties of the dyes on absorption and fluorescence spectra. At the same time, the absorption and emission spectral data of the closed form dyes 3a–e were compared with the open form dyes 2a–e due to more planarity of the closed form dyes that lead to the extension of the π–electron conjugation.