Engineering multifunctional Cyclen fluorophores for metal ion sensing, self-assembly and Nanocolloid applications

We report the design, synthesis, and comprehensive characterization of three novel monodansylated cyclen derivatives (L1-L3), each bearing alkyl side chains of varying lengths (n = 8, 12, 16), developed as multifunctional fluorophores. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) were employed to evaluate mesomorphism, a property often associated with extended alkyl chains. These compounds exhibited pronounced solvatochromic behavior and high fluorescence quantum yields, reaching up to 55 % in chloroform. The influence of solvent polarity on their photophysical properties was quantitatively analyzed using the Kamlet-Taft equation. Self-assembly behavior in THF-water mixtures revealed aggregation-induced emission (AIE), with emission profiles varying according to alkyl chain length, as confirmed by dynamic light scattering (DLS) and fluorescence lifetime measurements. Selective detection of Cu²⁺ and Hg²⁺ ions by L1 was demonstrated through significant fluorescence quenching, with detection limits of 2 μM and 40 μM, respectively. Speciation amount Cu²⁺/Cu⁺ and Hg²⁺/Hg⁺ was observed. Additionally, L3 functioned effectively as a stabilizing agent in the colloidal synthesis of platinum nanoparticles, resulting in spherical nanostructures with low polydispersity, as confirmed by transmission electron microscopy (TEM) and DLS. These results highlight the versatile utility of alkylated dansyl-cyclen hybrids as fluorescent probes with self-assembly properties useful as nanomaterial stabilizers for advanced functional applications.