Reversible end-to-end assembly of selectively functionalized gold nanorods by light-responsive arylazopyrazole–cyclodextrin interaction

Abstract

We propose a two-step ligand exchange for the selective end-functionalization of gold nanorods (AuNR) by thiolated cyclodextrin (CD) host molecules. As a result of the complete removal of the precursor capping agent cetyltrimethylammonium bromide (CTAB) by a tetraethylene glycol derivative, competitive binding to the host cavity was prevented, and reversible, light-responsive assembly and disassembly of the AuNR could be induced by host–guest interaction of CD on the nanorods and a photoswitchable arylazopyrazole cross-linker in aqueous solution. The end-to-end assembly of AuNR could be effectively controlled by irradiation with UV and visible light, respectively, over four cycles. By the introduction of AAP, previous disassembly limitations based on the photostationary states of azobenzenes could be solved. The combination photoresponsive interaction and selectively end-functionalized nanoparticles shows significant potential in the reversible self-assembly of inorganic–organic hybrid nanomaterials.

Reversible switching of arylazopyrazole within a metal–organic cage

“…Recently, much effort has been devoted to developing new families of heterocyclic azo switches [27–31], largely driven by the rapid growth of the emerging field of photopharmacology [32–34]. Among them, arylazopyrazoles have attracted considerable interest because of their synthetic availability and desirable photochemical properties, such as the high thermal stability of the Z isomer and a large band separation between the E and Z isomers, allowing each to be addressed with a high selectivity [35–40]. Consequently, arylazopyrazoles have been employed as photoresponsive gelators [41] and adhesives [42] and for controlling antimicrobial response [43–44], cell adhesion to surfaces [45], as well as DNA [46] and microtubule [47] self-assembly using light.…”

The Many Ways to Assemble Nanoparticles Using Light

“…Despite this diversity of methods enabling the control of NP self‐assembly using light, research in this field will continue to thrive, with several interesting directions outlined below. First, relatively little attention has been devoted to light‐induced self‐assembly of nonspherical NPs; with few exceptions, all the examples reported thus far are based on nanospheres. In principle, all of the approaches described above are applicable to NPs of other shapes, such as cubes and 2D prisms.…”

“…The AAP–β‐CD chemistry has also been employed for controlling the end‐to‐end assembly of rod‐shaped gold NPs . These nanorods are typically synthesized in water with the surfactant cetyltrimethylammonium bromide (CTAB).…”

“…To avoid any competition with AAP, a large excess of thiolated tetra(ethylene glycol) was added prior to the self‐assembly experiments, thus removing CTAB from the rods' side faces. Following this two‐step ligand exchange protocol, CD‐capped nanorods could reversibly be assembled and disassembled in the presence of a bis‐AAP linker upon exposure to green and UV light, respectively …”

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

“…Supramolecular structures can respond to external triggers including pH change [41][42][43], light [44][45][46][47][48][49][50], electrochemical stimuli [51,52], and temperature [53,54]. Of particular interest is the responsivity to light due to its non-invasiveness, which can be achieved with molecules that undergo photodimerization [55][56][57], photocleavage [58,59], and cis-trans photoisomerization [60][61][62][63][64][65].…”