Mixed N,O‐donor Directed Blue Emissive Nano‐dispersed Mesoporous Mn(II)‐MOF:Dual Sensing Probe for Recyclable and Ultrasensitive ppb‐Level Recognition of TNP and Cr(VI)‐Oxoanions

A new mesoporous Mn(II)-MOF [Mn2(phen)2(nia)2]∞ with 4-c uninodal net topology and reiterating rectangular channels in its cargo-net like extension was synthesized using π-conjugated phenanthroline (phen) and syn-syn bridging 5-nitroisopthalic acid (nia) linkers. The MOF (1) exhibited phase purity, uniform morphology, photo and thermal stability, and robustness; duly triggered by the exceptional framework rigidity via intermolecular H-bonding and interlayer π-π stacking interactions. The bright-blue luminescence of the MOF nano-dispersion was explored for sensitive, specific and ultrafast detection of trinitrophenol (TNP) with extremely low LOD (90.62 nM), high KSV (18.27 × 104 M-1) and Kq (4×1014 M-1s-1). The vapor-phase TNP sensing was also accomplished. Additionally, 1 served towards discriminatory, aqueous-phase monitoring of Cr(VI)-oxoanions, depicting LODs: 36.08 and 35.70 ppb; KSV: 3.46×104 and 4.87×104 M-1; Kq: 3.26×1013 M-1s-1 and 4.31×1013 M-1s-1;and response time: 32 and 40s for CrO42- and Cr2O72- respectively. The quenching mechanisms (i.e., RET, PET, IFE, weak interactions, collisional quenching and π···π stacking) was explained from several experimental investigations and theoretical DFT calculations. The recyclable sensing events and quantification from complex environmental matrices with admirable recovery rates and high KSV (13.02-22.44 × 104; ~6.31-10.98×104 and ~6.60-11.42 × 104 M-1 for TNP, CrO42- and Cr2O72-) undoubtedly advocated the consistency of the probe.