Strongly fluorescent organogels and self-assembled nanostructures from pyrene coupled coumarin derivatives: application in cell imaging

Abstract

Three different coumarin coupled pyrene derivatives with varying hydrophobic units (alkyl chains) have been synthesised and well characterized using NMR and mass spectral analysis. The gelation behaviour and self-aggregation properties of these compounds were studied relative to the molecular structure and solvent affinity. Among these derivatives, the one which is not having any hydrophobic tail displays efficient gelation in higher alcohols such as decanol and dodecanol. However the other derivatives having saturated and unsaturated hydrophobic tails form weak gel in different solvents. The morphology of gel was investigated by optical microscopy and high resolution transmission electron microscopy (HRTEM). The investigation of absorption and emission spectra of these compounds revealed that the photo-physical properties were significantly influenced by the self-assembly process in different solvents. The concentration dependent emission and ¹H NMR studies clearly suggest that the π–π stacking interaction and hydrogen bonding between carbonyl groups of coumarin coupled pyrene with the –OH group of solvent were the driving forces for the process of gelation and self-aggregation. Rheological investigation clearly demonstrates the flow behaviour and reversible nature of organogel under temperature and strain ramp up and ramp down experimental conditions. By getting clue from the self-assembly mechanism in different solvents, we derived nano-flakes from coumarin coupled pyrene derivatives and further explored their potential applications in the field of cell imaging. The size of the self-aggregated particles in the DMSO–water mixture has been identified using HRTEM and a zetasizer. The nanomaterials obtained via the self-assembly process were used for fibroblast and PC3 prostate cancer cell imaging applications. Further investigation reveals that these compounds suppress the proliferation of PC3 cells.