Synthesis of photoresponsive cholesterol-based azobenzene organogels: dependence on different spacer lengths.

Yuchun Ren,Bin Wang,Xiuqing Zhang

doi:10.3762/bjoc.11.122

Abstract

A series of azobenzene–cholesterol organogel compounds (M0–M12) with different spacers were designed and synthesized. The molecular structures were confirmed by 1H NMR and 13C NMR spectroscopy. The rapid and reversible photoresponsive properties of the compounds were investigated by UV–vis spectroscopy. Their thermal phase behaviors were studied by DSC. The length of the spacer plays a crucial role in the gelation. Compound M6 is the only one that can gelate in ethanol, isopropanol and 1-butanol and the reversible gel–sol transitions are also investigated. To obtain visual insight into the microstructure of the gels, the typical structures of the xerogels were studied by SEM. Morphologies of the aggregates change from flower-like, network and rod with different sizes. By using IR and XRD characterization, it is found that intermolecular H-bonding, the solvents and van der Waals interaction are the main contributions to the specific superstructure.

Highlights

In the past few decades, low molecular mass organic gelators (LMOGs) have attracted increasing attention for basic self-assembly behavior and for their potential application in areas such as templates [1], light harvesting [2], fluorescent scensing [3], etc
The photostationary state was attained after 94 min of irradiation and the spectral changes are attributable to the trans-to-cis isomerization under UV light irradiation
Upon UV–vis irradiation, these compounds can undergo a typical reversible trans–cis and cis–trans change due to the photo-isomerization of the azobenzene units. They possess recoverable photoresponsive properties. Their thermal phase behaviors have been investigated by differential scanning calorimetry (DSC), indicating good liquid crystal properties

Summary

Introduction

In the past few decades, low molecular mass organic gelators (LMOGs) have attracted increasing attention for basic self-assembly behavior and for their potential application in areas such as templates [1], light harvesting [2], fluorescent scensing [3], etc. A series of cholesterolbased gelators were reported [13,14,15] These new classes of organogelator architectures have been systematically studied because of their reversible gel process and unique directional self-association through weak van der Waals interactions [16,17]. A new multistimuli photoresponsive organogel containing azobenzene groups was designed and studied by D. Zhu and his co-workers [25]. We synthesized a series of compounds with different spacers between cholesteryl and azobenene units (Scheme 1). In these compounds, M6 is the only one that can gelate in ethanol, isopropanol and 1-butanol. It is found that intermolecular H-bonding, the solvents and van der Waals interaction are the main contributions to the specific superstructure

Results and Discussion

PI PPPP

Synthetic procedures

Conclusion