Trace-Level Humidity Sensing from Commercial Organic Solvents and Food Products by an AIE/ESIPT-Triggered Piezochromic Luminogen and ppb-Level “OFF–ON–OFF” Sensing of Cu²⁺: A Combined Experimental and Theoretical Outcome

Abstract

Selective and sensitive moisture sensors have attracted immense attention due to their ability to monitor the humidity content in industrial solvents, food products, etc., for regulating industrial safety management. Herein, a hydroxy naphthaldehyde-based piezochromic luminogen, namely, 1-{[(2-hydroxyphenyl)­imino]­methyl}­naphthalen-2-ol (NAP-1), has been synthesized and its photophysical and molecular sensing properties have been investigated by means of various spectroscopic tools. Owing to the synergistic effect of both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) along with the restriction of CN isomerization, the probe shows bright yellowish-green-colored keto emission with high quantum yield after the interaction with a trace amount of water. This makes NAP-1 a potential sensor for monitoring water content in the industrial solvents with very low detection limits of 0.033, 0.032, 0.034, and 0.033% (v/v) from tetrahydrofuran (THF), acetone, dimethyl sulfoxide (DMSO), and methanol, respectively. The probe could be used in the food industry to detect trace moisture in the raw food samples. The reversible switching behavior of NAP-1 makes it suitable for designing an INHIBIT logic gate with an additional application in inkless writing. In addition, an Internet of Things-(IoT) based prototype device has been proposed for on-site monitoring of the moisture content by a smartphone via Bluetooth or Wi-Fi. The aggregated probe also has the ability to recognize Cu2+ from a purely aqueous medium via the chelation-enhanced quenching (CHEQ) mechanism, leading to ∼84% fluorescence quenching with a Stern–Volmer quenching constant of 1.46 × 104 M–1 and with an appreciably low detection threshold of 57.2 ppb, far below than recommended by the World Health Organization (WHO) and the United States Environmental Protection Agency (U.S. EPA). The spectroscopic and theoretical calculations (density functional theory (DFT), time-dependent DFT (TD-DFT), and natural bond orbital (NBO) analysis) further empower the understanding of the mechanistic course of the interaction of the host–guest recognition event.

Theoretical Study on the Atom-Substituted Quinazoline Derivatives with Faint Emission as Potential Sunscreens

“… 38 − 40 Thus, it can be concluded that the IHB O 1 ···H 1 –N 1 is weakened at the S L state and verified that the reverse proton transfer (RPT) process prefers to proceed at the S 0 state. 41 Most notably, the relative ordering of the IHB intensity at S 0 and S L states for the three investigated compounds is as follows: HQ-k < HQS-k < HQSe-k. Based on the above analysis, it can be inferred that atomic electronegativity can alter the strength of IHB in the S 0 and S L states and thereby affect the proton transfer process of HQ. 41 …”

Novel Nanoporous Ti-Phosphonate Metal–Organic Framework for Selective Sensing of 2,4,6-Trinitrophenol and a Promising Electrode in an Energy Storage Device

“…The proposed host–guest interaction mechanism may be explained in terms of different sensing ways that include photoinduced electron transfer (PET), resonance energy transfer (RET), and intermolecular charge transfers (ICT) pathways. − In the case of PET, the presence of a low lying vacant π* orbital is necessary to accept an excited state electron from the donor fluorophoric unit. − Therefore, PET plays a pivotal role in the quenching efficiency of a particular fluorophore toward a particular analyte. In this context, DFT studies have been performed in order to understand the HOMO–LUMO energy levels of phosphonate MOF (H 8 L-Ti-MOF) and other targeted analytes.…”

Recent endeavours in the development of organo chromo-fluorogenic probes towards the targeted detection of the toxic industrial pollutants Cu2+ and CN−: recognition to implementation in sensory device

“…34). All the probes (35)(36)(37)(38) the PET process from the -N centres of the chemosensor skeleton to the vacant orbital of Cu 2+ . Accordingly, the detection limits were found to be 0.12 Â 10 À6 M, 0.10 Â 10 À6 M, 0.097 Â 10 À6 M and 0.098 Â 10 À6 M for 35-38, respectively.…”

“…Banerjee et al 36 exhibited a fluorogenic sensory probe, 8 , which could selectively detect aqueous Cu 2+ with a detection threshold of 57.2 ppb. In MeOH/H 2 O (60% v/v), 8 remained in the aggregated state, which led to the generation of strong AIE and ESIPT-induced greenish-yellow fluorescence.…”