Protan triggered colorimetric and fluorometric responsive coumarin coupled imidazole as Co2+ sensor, DFT and zebrafish bioimaging studies

Abstract

This study elucidates a novel Co²⁺ ion fluorescence chemosensor 6-bromo-3-(2-(2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazol-1-yl)thiazol-4-yl)-2H-chromen-2-one (NIC), which integrates imidazole and coumarin-thiazole moiety evolved over other frequently occurring metal ions. Fluorescence spectra are specifically used to study the complexation of NIC with different metal ions in an acetonotrile: water mixture (8:2) at room temperature. When Co²⁺ was present, NIC shows a notable quenching of fluorescence at 450 nm as a result of a complex forming which was accompanied by the emergence of a new band at 515 nm in the uv visible spectrum. Also, the colour of NIC was changed from yellow to brown which was evident from naked eyes. The sensor NIC demonstrated its high sensitivity towards Co²⁺ ions with a limit of detection (LOD) of 7 µM. The Job's plot validates the 1:1 binding stoichiometry between Co²⁺ and NIC. The chemosensor NIC also exhibited colorimetric and fluorometric sensing ability with a visible colorimetric response to Trifluoroacetic acid (TFA). Further, the study was also validated with zebrafish bioimaging studies.

Scheme 1

Representation of synthesis of NIC.

Fig. 1

UV-Vis. absorption (a), (c) and fluorescence emission (b), (d) of NIC in solvents with different polarity

Fig. 2

(a) UV-vis spectra of NIC (1 × 10^− 5 M) after addition of metal cations. (b) UV-vis spectra of NIC after adding 10 equivalents of Co²⁺ ions. (c) Visible colour and fluorescence changes of NIC with the addition of various metal ions.

Fig. 3

(a) Emission intensity of NIC at 450 nm as a function of Co²⁺ at different concentrations. (b) Benesi–Hildebrand linear analysis plot of NIC with change in concentration of Co²⁺.

Scheme 2

Representative of binding probability of NIC with Co²⁺.

Fig. 4

(a) Emission spectra of NIC with different metal ions. (b) Interference studies of NIC and Co²⁺ with different metal ions.

Fig. 5

Absorbance (a) and fluorescence (b) titration studies of NIC with TFA.

Fig. 6

Colorimetric and fluorescence changes of NIC with TFA and probable protonation to NIC.

Fig. 7

Frontier molecular orbitals (HOMO and LUMO) for NIC and NIC + Co²⁺.

Fig. 8

The optimized geometry and MESP map of NIC and NIC + Co²⁺.

Fig. 9

Toxicity observation of ligand NIC on D. rerio embryos for 24, 48, 72, and 96 hpf.

Fig. 10

Fluorescence images of live zebrafish larvae for NIC.