ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Sequential recognition of La³⁺ and CN⁻ ions using isophthalic dihydrazide derivative via aggregation induced enhanced emission (AIEE): a fluorescence relay enhancement in aqueous medium

Vaishali Yadav and Vimal K. Bhardwaj

Department of Chemistry, Dr B R Ambedkar National Institute of Technology, Jalandhar, India

E-mail: bhardwajvk@nitj.ac.in

Received: 3 October 2022  Accepted: 12 December 2022

Abstract:

An isophthalic dihydrazide based Schiff base receptor H₂L has been explored for the sequential sensing of La³⁺ and CN⁻ ions in aqueous medium with fluorescence relay enhancement, having a detection limit of 5.90 × 10^–8 M and 4.47 × 10^–7 M, respectively. The fluorescent aggregates of H₂L have been synthesized by re-precipitation method to overcome the weak fluorescence property of La³⁺ion via aggregation induced enhanced emission (AIEE) mechanism. The absorption and emission sensing studies of receptor H₂L have been performed towards various metal ions such as Th³⁺, Ce³⁺, Eu³⁺, Ho³⁺, Pr³⁺, Cd²⁺, Hg²⁺,Co²⁺, Zn²⁺, Cu²⁺, Ni²⁺ as their nitrate salts in 20 mM N-(2-hydroxyethyl)-piperazine-N′-ethanesulfonic acid (HEPES) buffer solution at neutral pH in H₂O–DMSO (95%, v/v). The addition of La³⁺ ion solution to H₂L aggregates results in a remarkable emission enhancement at 748 nm with a detection limit of 5.90 × 10^–8 M. The aggregates of resultant H₂L-La complex have also been investigated for the sensing of different anions such as F⁻, Cl⁻, Br⁻, SO₄⁻, H₂PO₄⁻, N₃⁻, AcO⁻, I⁻, NO₃⁻ in H₂O–DMSO (60%, v/v) at neutral pH. However, the presence of CN^‒ ion to H₂L-La complex solution further exhibits a fluorescence relay enhancement with 4.47 × 10^–7 M limit of detection. The observed behaviour is due to chelation enhanced fluorescence (CHEF) by metal ion and effective interference in the photoinduced electron transfer (PET) quenching by anion. The interaction studies of receptor with La³⁺ and resultant H₂L-La complex with CN⁻ ion are supported by mass spectrometry. It is the first report on fluorescence relay enhancement for the sequential recognition of La³⁺ and CN⁻ions.

Keywords: Chelation enhanced fluorescence (CHEF); Fluorescent sensors; Imine receptor; Excited state intramolecular proton transfer (ESIPT); Nano-aggregates

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02633-y

Chemical Papers 77 (5) 2425–2435 (2023)