The influence of bonding topology on the electronic properties of new Schiff bases containing phenothiazine building blocks

• Microwave assisted synthesis of mono- and bis-phenothiazinyl-azomethines.
• Systematic variation of the azomethine position on the phenothiazine building block
• Phenothiazinium/phenothiazine redox couple emphasized by cyclic voltammetry.
• Positive solvatochromism of fluorescence emissions in the visible region (471–597 nm)

Series of new heterocyclic Schiff bases enclosing a systematic variation of the azomethine linker position on the phenothiazine building block were advantageously obtained by the microwave assisted condensation of constitutional isomers of 10-methyl-10Hphenothiazine-carbaldehyde with primary aryl-amines (2-aminonaphthalene, 2-aminofluorene, 2- and 3-amino-10-methyl-phenothiazine respectively). Their electronic properties were emphasized by means of UV–Vis absorption/emission spectroscopy and cyclic voltammetry. The phenothiazine chromophore unit appeared responsible for large Stokes shifts of the UV absorption maxima towards emission maxima situated in the visible range (471–597 nm) largely influenced by the variation of the solvent polarity. Cyclic voltammetry experiments emphasized reversible redox processes suggesting the formation of phenothiazinium radical cation species in consecutive steps correlated to the number of phenothiazine units embedded in the molecular structure. The experimental outcomes and computational data simulating the molecular orbitals of the synthesized phenothiazine derivatives were corroborated for a rational understanding of the similarity in the properties of congeners.

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