Triphenylamine-derived fluorescent sensor for relay detection of iron(iii) and aliphatic biogenic amines

Abstract

This manuscript introduces a Schiff base, IBS, synthesized by condensing equimolar amounts of 4-(diphenylamino)benzaldehyde and 1,2-diaminobenzene. The IBS was employed for the cascade fluorescence ‘off–on’ detection of Fe³⁺ and biogenic amines. The fluorescence emission behaviour of IBS was explored in a mixed DMSO:H₂O medium by increasing the water fraction (f_w) from 0 to 95%. The cyan-blue-emitting IBS (f_w = 60%) was employed for the fluorescence turn-off detection of Fe³⁺. The Schiff base IBS emission at 468 nm was selectively quenched by Fe³⁺, with a distinct visual change from cyan-blue fluorescence to no fluorescence. Static quenching was proposed based on the UV-Vis and fluorescence lifetime results. The IBS-Fe³⁺ complex was formed in a 2 : 1 binding stoichiometry with an estimated binding constant of K₁₁ = 53 359.73 M⁻¹ and K₂₁ = 8322.04 M⁻¹. The detection limit of IBS for Fe³⁺ was found to be 2.19 × 10⁻⁷ M. Subsequently, the in situ generated IBS-Fe³⁺ complex was employed for the fluorescence turn-on sensing of biogenic amines. The addition of aliphatic polyamines, such as putrescine, spermidine, spermine and cadaverine, restored the fluorescence emission at 468 nm, with a nanomolar detection limit of 3.24 nM. The IBS-Fe³⁺ complex was spectroscopically silent towards aromatic and heterocyclic amines (tryptamine and tyramine). The practical utility of IBS and IBS-Fe³⁺ was explored by detecting Fe³⁺ and aliphatic biogenic amines in real samples.