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

Investigation of fluorenyl-thioic-based ditopic as a functional colorimetric probe for heavy metal cations and anions with higher selectivity towards Cu²⁺ followed by Zn²⁺, displaying logic functions: Experimental and computational studies

Paulina T. Endjala, Johannes Naimhwaka, and Veikko Uahengo

Department of Chemistry and Biochemistry, University of Namibia, Windhoek, Namibia

E-mail: vuahengo@unam.na

Received: 24 January 2021  Accepted: 4 June 2021

Abstract:

A fluorenyl-thioic-based dye (P) bearing a thioic ester moiety was designed, synthesized and spectroscopically characterized. The photophysical properties were studied via UV–Vis spectroscopy in acetonitrile (CH₃CN) as a solvent of choice. Upon investigating and studying the photophysical properties, it was found that P could be an ideal colorimetric sensor for biologically important anions and cations. The chemosensing properties were studied through naked eye observable colour changes as well as UV–Vis titration method. The naked eye observations and UV–Vis titrations established that P is a colorimetric probe selective and sensitive to some cations (Ag⁺, Hg²⁺, Ni²⁺, Fe³⁺, Co²⁺, Cu²⁺ and Zn²⁺) and anions (F⁻, CN⁻, OH⁻ and AcO⁻) in CH₃CN. The nature of interaction with cations is via coordination by soft atoms (nitrogen and sulphur atoms), in the process inducing spectral red shift (375 to 475 nm), whereas interaction with anions was dominated by hydrogen bonding, leading to yet another red shift (375 to 453 nm). The cross-detection studies have indicated that M has more affinity towards Cu²⁺, followed by Zn²⁺, compared to all other cations used. The reversibility and reproducibility studies were carried out, and P was found to exhibit molecular logic behaviours, thereby displaying complementary IMP/INH logic functions, based on colour and spectral switching (ON/OFF). Hence, the probe can thus be utilized as a colorimetric molecular switch modulated by F⁻/Al³⁺. In addition, the experimental data were supplemented by computational calculations, where HOMO and LUMO levels at − 5.65 and − 2.51 eV (3.14 eV energy gap) for P were well in agreement with the absorption curve.

Keywords: Fluorenyl-thioic dye; Ni(II) and Co(II) sensor; Dual sensor; Molecular logic functions

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-021-01736-2

Chemical Papers 75 (10) 5471–5488 (2021)