Exploring Colorimetric Real-Time Sensing Behavior of a Newly Designed CT Complex toward Nitrobenzene and Co²⁺: Spectrophotometric, DFT/TD-DFT, and Mechanistic Insights

Abstract

An exceptionally unique, easy-to-prepare, and economic charge transfer complex (CTC), [(IMH) + (PA) − ], was synthesized as a highly selective real-time colorimetric chemosensor material for nitro explosive nitrobenzene (NB) and Co 2+ ion. Co 2+ and NB are highly potential toxic and hazardous beyond the exposure limits and also classified as carcinogens (group 2B) by IARS and United States Environmental Protection Agency. Unusual sensing ability with appreciatively low detection limits of 0.114 and 0.589 ppb for NB and Co 2+ ion, respectively, in the aqueous medium of dimethyl sulfoxide has been reported for the first time among this class of complexes reported so far. The mechanism of the tremendous sensing behavior of this material as chemosensor was ascertained by static quenching mechanism, Dexter electron transfer, and Forster resonance energy transfer dynamic quenching mechanism, which was supported by spectral overlapping and density functional theory (DFT) (B-3LYP/def2-SVP) calculations. Real-time colorimetric sensing behavior of chemosensor was demonstrated by the naked eye test and prestained paper Co 2+ strip test. Job’s plot and comparative Fourier transform infrared (FTIR) study between CTC and CTC–Co 2+ complex revealed the coordination mode between CTC and Co 2+ ion and 2:1 stoichiometry. This sensing material [(IMH) + (PA) − ] was synthesized with donor imidazole (IM) and acceptor picric acid (PA), and its characterization was achieved by experimental (single-crystal X-ray diffraction, thermal gravimetric analysis–differential thermal analysis, FTIR, and UV–vis studies) and theoretical methods [DFT/TD-DFT calculations, comparing experimental–theoretical data and obtaining MEP map along with electronic energy gap of HOMO → LUMO (Δ E = 3.545 eV) and Hirshfeld surfaces analysis]. The SC-XRD confirms the composition and bonding features, which show hydrogen bond via N + –H···O – between IM and PA. This N + –H···O – interaction plays a significant role in Co 2+ binding, proving this method of synthesizing CTC as a chemosensor to be a novel approach.

One-pot synthesis, molecular docking, ADMET, and DFT studies of novel pyrazolines as promising SARS-CoV-2 main protease inhibitors

“…Figure 13 represents the spatial arrangements of HOMO and LUMO along with their gap and associated energies. The HOMO–LUMO gap (∆ E ) for compounds A1 , A2 , and A3 were calculated to be 3.216, 3.156, and 2.622 eV, respectively [ 53 ]. On the basis of ∆E, the chemical reactivity of the compounds is arranged in the following sequence— A1 > A2 > A3 .…”

Spectroscopic and Molecular Docking Studies of Cu(II), Ni(II), Co(II), and Mn(II) Complexes with Anticonvulsant Therapeutic Agent Gabapentin

“…The HOMO (−4.2308 eV) to LUMO (−1.6620 eV) energy gap (∆E) was calculated to be 2.5687 eV. The spatial arrangements of the HOMO-LUMO, associated energies, and gap are represented in Figure 19 [52][53][54]. Some molecular parameters in the gas phase, based on HOMO-LUMO and optimized geometry, are presented in Table 8.…”

Applications of Density Functional Theory on Heavy Metal Sensor and Hydrogen Evolution Reaction (HER)

“…The real time experiment was explored with river water samples. The imidazole based receptor was reported by Khan et al [48] to sense picric acid (donoracceptor) for detection of toxic nitrobenzene through static quenching, Dexter electron transfer and Forster resonance energy transfer quenching mechanisms. The HOMO and LUMO orbital energies were obtained at B3LYP/6-31 g(d) level as −3.00 eV and −6.91 eV for the probe and the HOMO and LUMO energies were found to be −3.15 eV and −7.64 eV upon binding with nitrobenzene.…”