Multi-stimuli Responsive Supramolecular Structures Based on Azobenzene Surfactant-Encapsulated Polyoxometalate

Abstract

Multi-stimuli responsive materials have attracted intense attention as extensive application prospect in many fields, yet achievement of multi-stimuli responsiveness remains a challenge. Herein, we report a tri-stimuli responsive supramolecular structure fabricated by a cationic surfactant, 4-ethyl-4'-(trimethylaminohexyloxy) azobenzene bromide (ETAB), and anionic Eu-containing polyoxometalates (Eu-POM), based on an ionic self-assembly (ISA) strategy. Following different responsive mechanisms, the resultant ETAB/Eu-POM supramolecular materials are responsive to UV light, pH, and Cu(2+), respectively. The response to UV irradiation is based on the configuration change of azobenzene molecules. The response to H(+) can be attributed to the formation of a hydrogen bond W-O···H···O-H among Eu-POM, H(+), and H2O, which blocks the energy transfer pathway from O → W, while the coordination interaction between Cu(2+) and Oc (bridged oxygen of two octahedra sharing an edge in the Eu-POM molecule) causes the response to Cu(2+). The multi-stimuli responsive characteristics for the ETAB/Eu-POM supramolecular structures maybe provide a potential application in ultraviolet detection, optical storage devices, and chemical substance sensors, etc.

Unlocking Structure–Self-Assembly Relationships in Cationic Azobenzene Photosurfactants

“…AzoTAB surfactants have received significant attention for their potential applications, for example in the design of light-responsive gels [25][26][27] and DNA, [28][29][30] modified graphene oxide, [31][32] photomanipulation of droplets, 8 templating 33 and photoluminescent complexes. 34 In contrast, little has been done to determine the relationship between molecular design and function in AzoTABs. Hayashita et al studied the effect of the length of the hydrophobic segment (R1 + R2 < 10) of AzoTABs in the trans-and cis-forms and determined that an increase in the length of the alkyl tail (R1) led to a decrease in both the absolute conductivity and CMC.…”

Self-Assembly of Europium-Containing Polyoxometalates/Tetra-n-alkyl Ammonium with Enhanced Emission for Cu2+ Detection

“…The results showed that both the morphology and structure were barely affected by Cu 2+ , indicating that the energy release from the O → W LMCT excited state transferred to Cu 2+ rather than the 5 D 0 emitting state of Eu 3+ is the possible reason for the fluorescence quenching. 58 Specifically, as Cu 2+ diffused into the solution and came close to the Eu 3+ ion surface, the energy transfer was more efficient for the smaller sized nanoparticles and externally distributed EuW 10 . 59…”

Coassembly of a Polyoxometalate and a Zwitterionic Amphiphile into a Luminescent Hydrogel with Excellent Stimuli Responsiveness

“…The calculated interplanar distance of xerogel (1:1) was 4.26 nm, which is larger than that of pure C 20 IPS. It is known that the transverse and longitudinal lengths of EuW 10 are about 0.8 and 1.44 nm, respectively (Scheme b) . Given the water solubility and charged character, the EuW 10 tends to approach the hydrophilic head group of C 20 IPS.…”