Photochemical synthesis of indazolo[3,2-b]quinazolines and their redox-switching properties

• Several indazolo[3,2-b]quinazolines were photochemically synthesized.
• A nitrene-mediated cyclization mechanism was proposed.
• N-methylation blocks the light-sensitive properties.
• The heterocycles exhibit reversible redox-switching properties.

Several indazolo[3,2-b]quinazolines were synthesized in moderate to good yields by exposing 2-(2-nitrophenyl)-1,2,3,4-tetrahydroquinazolines to UV light (306 nm) in acetonitrile. The scope, limitation, and possible mechanism of this light-mediated reaction as well as the redox-switching properties of the target compounds were explored. Reduction of the colored indazolo[3,2-b]quinazoline with sodium borohydride resulted in a distinct change to colorless and a sharp increase in fluorescence intensity. The reduced product can be swiftly reverted to the original form by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone oxidation. The reversible redox-switching between the indazolo[3,2-b]quinazoline and its reduced product utilizing chemical reduction and oxidation as two external stimuli with dual output properties; that is, color change and emission variation was reported.

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