From visible to far-red excitable chromophores derivatives of vitamin B6. Evaluation as pH-responsive probes and solvatochromic study

• Vitamin B6 derivatives bearing visible excitable chromophores.
• pH responsive probes in aqueous media.
• Positive solvatochromic effect.

Owing to the great potential and application of pH probes in biological and environmental sciences, four aqueous soluble vitamin B6 derivatives 1–4 bearing visible excitable chromophores as coumarin, fluorescein, cresyl violet and nile blue were successfully synthetized and characterized. Compounds 2–4 are highly pH dependent revealed significant spectral changes in the ground and excited states, with exception of 1 whereas no changes in the excited state were visualized. In the same way, at pH 6–7 probes 1 and 3 exhibited the highest fluorescent quantum yield, with values of 0.65 and 0.51. Concerning the solvatochromic behaviour, a positive effect was witnessed for compound 4. Moreover, in the excited state were observed different colours ranging from red (CH2Cl2) to orange (CHCl3, CH3CN), to pink (EtOH), to green (DMSO) and to blue (H2O). The dipole moments in the ground and excited states were determined for compound 4, whereas values of μg.imineE = 3.62 D, μe.imineE = 12.35 D (Δμ = 8.73 D), μg.iminez = 3.38 D and μe.iminez = 11.54 D, (Δμ = 8.16 D), revealing that 4 is more polar in the excited state.

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