Unravelling the interplay between structures, self-assembly patterns, AIEE and chiroptical properties of NDI-bis-cholesteryl systems

Abstract

Naphthalene diimides (NDIs) offer exquisite optical and electronic properties and find a broad range of applications in various chemical and biomedical fields. However, due to their flat structure, at higher concentrations, the emission from NDIs gets severely quenched. The restoration of luminescence in such an interesting class of molecules has been widely explored through the tuning of their optical properties via synthetic modification, supramolecular self-assembly and aggregation induced emission (AIE) techniques. Here, we aim at highlighting the role of the spacer group in the tuning of the chiroptical properties of NDIs through a self-assembly approach, using a bis-cholesteryl diimide system. Three NDI-bis-cholesteryl systems have been prepared and their self-assembled structures, optical and chiral properties in monomeric and aggregated states have been studied. Microscopic investigations reveal almost identical morphology in aggregates, however, quite different aggregation behaviour and chiroptical properties in the ground and excited states are observed. Circular dichroism (CD) studies revealed an interesting medium controlled enhancement and reversal of chiral properties in the self-assembled structures.