Cholesterol-tethered AIEE fluorogens: formation of self-assembled nanostructures

Abstract

Design and synthesis of cholesterol conjugated chromophores exhibiting intramolecular charge transfer (ICT) and Aggregation Induced Enhanced Emission (AIEE) is described. Cholesterol conjugated a-cyanostilbene exhibits weak emission in organic solvents but in aqueous media this shows 5-fold intensity increase accompanied by a strong bathochromic emission shift as a consequence of AIEE effect. On the other hand, cholesterol conjugated diene exhibits quenched emission in water with characteristic polarity dependent solvatochromic emission shifts. Under aqueous conditions and in sodium cholate matrix, cholesterol stilbene conjugate self-assembles to form organized nanostructures having distinct morphological differences to the structures observed in the absence of cholesterol tether. The self-assembled structures were characterized using scanning electron microscopy and circular dichroism.

α-Cyanostilbene: a multifunctional spectral engineering motif

“…The π-conjugation length of SK7 was extended to generate SK8 by incorporating a diene unit and the impact of conformational flexibility on the SLE activity was correlated. 100 SK8 demonstrated moderate SLE characteristics because of the increased conformational flexibility by the additional CC bond, which freed the α-cyano unit to undergo dynamic IMR. Hence, the synergistic combination of conformational flexibility from the π-framework and flexible aliphatic chains from the cholesterol unit remarkably quenched the aggregates emission.…”

Cholesterol-Based Compounds: Recent Advances in Synthesis and Applications

“…In 2015, Palakollu and Kanvah designed and synthesized cholesterol-conjugated chromophores of α-cyanostilbene/diene 338 and 340 exhibiting intramolecular charge transfer (ICT) and aggregation-induced enhanced emission (AIEE). Compounds 338 and 340 were easily prepared from the reaction of cholesterol chloroformate 7 with either a stilbene 337 or diene derivative 339 (Scheme 81) [87].…”

“…Nevertheless, the most interesting conclusion of the optical properties study was that the random aggregates formed by stilbene 337 in aqueous media became highly ordered upon cholesterol conjugation 338 . Furthermore, the interaction with sodium cholate stimulated the formation of self-assembled structures in nanoscale dimensions, making these conjugates the starting point for the development of several bioimaging probes [87].…”

Exploring the self-assembly dynamics of novel steroid–coumarin conjugates: a comprehensive spectroscopic and solid-state investigation

“…Extrinsic fluorescent probes that combine steroids with small fluorophores, such as α-cyanostilbene-cholesterol and bile acids conjugated with tetraphenylene, dansyl, and α-cyanostilbene have been used for the selective detection of H 2 O 2 , as well as for the creation of nanomaterials and organogels. [27][28][29][30][31][32] Studies on conjugates of cholesterol-coumarin 33 and various bile salts with 7-diethylamino-4-methylcoumarin 34 have addressed supramolecular interactions, however, the impact of steroids on coumarin aggregation and cell localization remains relatively unexplored.…”