A multichannel fluorescent sensor for solid and vapor phase detection of 4-nitroaniline and salicylaldehyde with latent fingerprint and an invisible ink analysis: Extensive experimental and DFT studies

Abstract

Organic fluorophores with extensive aromaticity are crucial while designing sensors with outstanding optical characteristics. Herein, we synthesized a novel fluorescein based organic fluorophore 2-((anthracen-9-ylmethylene) amino)-3′,6′-dihydroxyspiro[isoindoline-1,9′-xanthen]-3-one (ADX) demonstrating exceptional photophysical properties. We conducted a comprehensive examination of fluorescence properties of the sensor ADX, exploring various aspects including aggregation, solvatochromism, solid and vapor phase studies using fluorescence emission, UV Vis. and other spectroscopic analysis. Notably, fluorophore exhibits aggregation induced emission (AIE) character, marked by a substantial Stokes shift of 78 nm. This characteristic was comprehensively evaluated in a water/DMF (9:1, v/v) binary solvent system, which facilitated the designing of latent fingerprint detection and an invisible ink. Furthermore, admirable optical properties of sensor ADX were utilized for efficient and selective sensing of 4-nitroaniline (4-NA) with “Turn Off” and salicylaldehyde (SA) with “Turn On” fluorescence in real water samples. Calculated limit of detection (LOD) was 165 nM and limit of quantification (LOQ) was 549 nM for 4-NA while 31.4 nM and 104.6 nM for SA, respectively. To further enhance practical applications, we developed a portable paper-based strip for on-site sensing of 4-NA and SA. Additionally, we thoroughly evaluated the mechanistic approach for the detection of 4-NA and SA through NMR, ultraviolet–visible (UV–Vis.) and photoluminescence spectroscopic techniques along with DFT studies. DFT studies include the calculation of reduced density gradient (RDG), thermodynamic stability, charge transfer and QTAIM analysis. Collectively, our experimental and theoretical investigations support the existence of weak intermolecular interactions among sensor ADX and analytes (4-NA and SA).