Mechanism‐Driven Bioactive Indazole Frameworks: Photoinitiated Demethylation‐Aromatization Synthesis and Biosensing Applications

Indazole frameworks are pivotal in medicinal chemistry and fluorescent conjugate design. Herein, we reported a photochemical strategy enabling efficient N‐demethylation and aromatic cyclization of N‐methyl amines via UV‐induced nitroso intermediates, offering an environmentally benign route to structurally diverse 2H‐indazole scaffolds. Diverging from conventional methods, this protocol demonstrates exceptional substrate compatibility with various alkyl/aryl amines, facilitating streamlined assembly of functionalized 2H‐indazole modules. The methodology has been successfully applied to synthesize modified drugs and tumour‐specific fluorescent probes targeting G‐quadruplexes. Preliminary evaluations of physiological toxicity and cellular fluorescence imaging highlight their biomedical potential, establishing these strategies as potential tools for pharmacological development and bioimaging research.