Solvatochromism, anion binding and electrochemistry in 5,15-porphodimethenes

•Excellent positive absorption solvatochromism.•The porphodimethenes display remarkable colorimetric response towards OH− and F− ions.•The colorimetric chemosensor acts as potential probe towards polar solvents.•Tautomeric behaviour is responsible for the observed color change and anion binding.

Synthesis and characterization of substituted 5,15-bis-(4′-hydroxy-3′,5′-di-tert-butyl-phenyl)-porphodimethenes (3a-b), are described. Spectroscopic studies of redox-active 3,5-di-tert-butyl-4-hydroxyphenyl substituted porphodimethene 3a, 3b reveal a change in conformation via acid/base-switched tautomerism by simultaneously switching between porphodimethene and porphyrinogen accompanied by visible chromogenic changes. The novel prototype exhibits a positive solvatochromism and chromogenically senses fluoride (specifically in polar solvents) and hydroxide ion (in all solvents). The unique structural changes along with distinct color changes were monitored by UV-Vis, fluorescence, cyclic voltammetry NMR spectroscopic techniques and DFT computations.

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