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.