Unraveling Molecular Assembly and Tracking Lipid Droplet Dynamics Using Fluorescent Phenanthroimidazole Derivatives

Small strategic perturbations of the molecular structures impart significant variation in the evolution dynamics and properties of supramolecular self-assembled architectures. However, probing the in situ evolution dynamics of molecular assembly remains a challenge. Herein, we unraveled the real-time, early stage environment-sensitive dynamic molecular self-assembly processes and stimuli-induced reversible morphological transformation between supramolecular fibers and spherical nanoaggregates of alkyl chain-substituted phenanthroimidazole-based luminogen (BPIB1) through fluorescence lifetime imaging microscopy (FLIM). The presence of an octyl chain and basic nitrogen centers in BPIB1 led to a distinct self-assembly pattern. The gradual progression in the fluorescence lifetime provides a unique strategy for elucidating the dynamics of the self-assembly process leading to distinct nano/microarchitectures. Among the varied self-assembled structures, the smaller-sized (diameter ∼ 20–30 nm), highly photostable, water-dispersible, and biocompatible fluorescent nanoaggregates of BPIB1 were employed for tracking the dynamics of lipid droplets in live cells and a model organism, C. elegans, using fluorescence correlation spectroscopy and FLIM. Thus, a combined microscopic and spectroscopic approach demonstrated in the present study opens up new avenues to explore the formation pathways of diverse molecular aggregates and their use to decipher complex organelle dynamics.