Issue 24, 2021

Aggregation-induced emission (AIE)-active N-arylated ferrocenyl pyrazole chromophores: second-order nonlinear optical and turn on/off fluorescence for the detection of picric acid in mixed aqueous media

Abstract

A series of new donor–acceptor (D–A)-type N-arylated ferrocenyl pyrazole chromophores 1–4 have been synthesized and spectroscopically characterized. The molecules 2–4 crystalize in the centrosymmetric space group, but show a weak second harmonic generation (SHG) effect in bulk due to the presence of non-covalent interactions reducing the anti-parallel alignments. The absorption properties were examined in a wide range of solvents from polar to non-polar, shows a positive solvatochromism, because of the larger dipole moment in the excited state. All the derivatives exhibit weak emission in the solution state (CH3CN: H2O), owing to the quenching nature of ferrocene, but strong emission was observed in their aggregated state because of the restriction of intramolecular rotation, and this phenomenon is known as aggregation-induced emission (AIE). The AIE-state is further utilized to detect picric acid in a mixed aqueous medium by a fluorescence turn on/off method. It was carried out in a water fraction of fw = compounds 1 and 2 at 80%, and compounds 3 and 4 at 90%, which shows highly selective and sensitive fluorescence quenching response towards picric acid in a mixed aqueous solution among several nitroaromatic compounds. The density functional theory revealed that the fluorescence quenching mechanism is a photo-induced electron transfer process between N-arylated ferrocenyl pyrazole and picric acid. The low quenching constant (Ksv = 2.54 × 107 M−1) and detection limit (25.4 nm) of picric acid was observed in compound 1, due to the presence of π-electron-rich delocalization over the aromatic ring, which interact with picric acid via non-covalent interactions that make effective charge transfer from N-arylated ferrocenyl pyrazole to picric acid.

Graphical abstract: Aggregation-induced emission (AIE)-active N-arylated ferrocenyl pyrazole chromophores: second-order nonlinear optical and turn on/off fluorescence for the detection of picric acid in mixed aqueous media

Supplementary files

Article information

Article type
Research Article
Submitted
17 Jul 2021
Accepted
19 Okt 2021
First published
19 Okt 2021

Mater. Chem. Front., 2021,5, 8290-8307

Aggregation-induced emission (AIE)-active N-arylated ferrocenyl pyrazole chromophores: second-order nonlinear optical and turn on/off fluorescence for the detection of picric acid in mixed aqueous media

E. David, K. Thirumoorthy and N. Palanisami, Mater. Chem. Front., 2021, 5, 8290 DOI: 10.1039/D1QM01022K

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