Phenanthroimidazole-based fluorescent nanofibers with 2-thiohydantoin for mercury detection and plant tissue...

Herein, we have designed a novel fluorescent probe, Phen-2TH, using a one pot Knoevenagel reaction between Phen-CHO and 2-thiohydantoin with 84 % yield, and is characterized by various spectroscopic techniques like FTIR, ¹H{¹³C} NMR and LC-MS. Phen-2TH exhibited a strong absorption band at ∼419 nm with a green fluorescence at λ_max = 525 nm in pure THF and show an excellent solvatochromic properties with a large bathochromic shift by varying the solvent polarities. Phen-2TH form a distinct self-assembled structures like needles, nanofibers and nano-aggregates with variations in the hydrophilic and hydrophobic media (THF: H₂O). Particularly, the emission behaviour significantly alters from green to orange with variation in the hydrophobic environment. At f_w = 70 %, the emission maxima exhibited a red shift towards orange emission at ∼640 nm. Phen-2TH shows a unique turn-OFF fluorescence response behaviour towards the detection of Hg²⁺ ions in aqueous media a LOD of ∼55 pM with K_sv of 6.3 × 10⁴ M^-1. Job's plot analysis and ¹H NMR mechanistic investigations reveal the formation of 2:1 stoichiometry between Phen-2TH and Hg²⁺. Mercury binds to the thiohydantoin unit and weakens the ICT process due to its diamagnetic nature. Furthermore, the potential of the probe for real-time monitoring of Hg²⁺ in various environments, including deionized water, milk, fish, and sprouted pea roots were analyzed through fluorescence imaging. A smartphone-assisted RGB-based color recognition array approach is implemented for the qualitative and quantitative analysis of Hg²⁺ ions with an LOD of ∼77 μM. The study demonstrated herein provides a promising approach for the real-time monitoring of contaminations in the food and other toxic pollutants.