Multifunctional fluorescent ionic liquid crystals based on L-tryptophan and gemini surfactants for Cu(II) and ascorbic acid detection in real samples.

Abstract

Ionic liquid crystals (ILCs) represent a promising and innovative subclass of ionic liquids, recognized for their exceptional performance. This study investigates the potential of newly synthesized ILCs, featuring two imidazole rings connected by a three-carbon spacer and the groups of added amino acid L-tryptophan (L-Trp). The ILCs were characterized using FT-IR, ¹H NMR, ¹³C NMR, the mass spectral technique and XRD analysis. Circular dichroism (CD) spectroscopy was applied to examine the chiroptical properties of L-Trp and the synthesized ILCs, [C_<i>n</i>Im3OHImC_<i>n</i>]·2Trp (<i>n</i> = 12, 14, 16). Confocal laser scanning microscopy (CLSM) was utilized to study the morphology and luminescence of these ILCs. The three distinct ILCs with varying chain lengths were designed and synthesized to function as a novel fluorescent sensor for Cu²⁺ ion and L-ascorbic acid (AA) detection and their linear range and LOD were found to be 7.97-106 μM and 4.59, 6.22 and 5.11 μM for the former and 3.99-40.00 μM and 3.42, 4.11 and 3.55 μM for the latter analyte. However, the variation of the alkyl chain length for the synthesized ILCs did not show any noticeable effect on their fluorescence behaviour. Job's plot confirmed a 2 : 1 coordination mode between the ILCs and Cu²⁺ ions. Practical applications were validated through the analysis of real-world samples, specifically for the detection of Cu²⁺ and AA in real samples like coffee, black tea, green tea and tomato, pomegranate, orange, and human blood serum (HBS), respectively. This study highlights the potential of imidazolium-based ILCs as efficient fluorescent sensors for Cu²⁺ and AA detection in real sample assessments.