Photoswitchable NIR‐Emitting Gold Nanoparticles

Abstract

Photo-switching of the NIR emission of gold nanoparticles (GNP) upon photo-isomerization of azobenzene ligands, bound to the surface, is demonstrated. Photophysical results confirm the occurrence of an excitation energy transfer process from the ligands to the GNP that produces sensitized NIR emission. Because of this process, the excitation efficiency of the gold core, upon excitation of the ligands, is much higher for the trans form than for the cis one, and t→c photo-isomerization causes a relevant decrease of the GNP NIR emission. As a consequence, photo-isomerization can be monitored by ratiometric detection of the NIR emission upon dual excitation. The photo-isomerization process was followed in real-time through the simultaneous detection of absorbance and luminescence changes using a dedicated setup. Surprisingly, the photo-isomerization rate of the ligands, bound to the GNP surface, was the same as measured for the chromophores in solution. This outcome demonstrated that excitation energy transfer to gold assists photo-isomerization, rather than competing with it. These results pave the road to the development of new, NIR-emitting, stimuli-responsive nanomaterials for theranostics.

Highly Luminescent Folate‐Functionalized Au22 Nanoclusters for Bioimaging

“…That is, FA is fluorescent and has good spectral overlap with the absorption of Au 22 cluster. It is thus possible to photoexcite the FA pendants to sensitize the Au 22 cluster by resonance energy transfer . To examine this possibility, Au 22 ‐FA was photoexcited at 350 nm and the resulting PL was compared with that resulted from 520 nm excitation.…”

Towards Ultra‐Bright Gold Nanoclusters

“…More recently, we proposed a different strategy to turn on/off the PL of Au 144 NCs using as organic sensitizer a photo‐switchable azobenzene derivative (Figure ) . The conversion of the trans form of the ligand into the cis one took place almost quantitatively (> 95 %) with a quantum yield identical to the one measured for the same molecule free in solution (upon irradiation at 360 nm).…”

“…In order to improve this feature, our and other groups proposed the design of hybrid structures that combine the PL properties of Au NCs with the optical properties of organic dyes in order to enhance the brightness of the inorganic emitters. A considerable improvement of brightness can in fact be achieved by introducing ligands able to efficiently adsorb light (chromophores) and to transfer the excitation energy to the emitting gold core , …”

Molecular control over colloidal assembly

“…diagnostics upon further optimisation and transposition from chloroform to physiologically relevant conditions. 142 The Klajn group reported acceleration and altered stereoselectivity in 'self-assembling nanoflasks' for various chemical reactions in water-saturated toluene upon confinement of small molecules within the 'interstitial' spaces of supraparticles assembled from AuNPs coated with light-responsive ligands. 143 Qu and co-workers reported enhanced catalytic activity and high enantioselectivity of microbes encapsulated in a W/O Pickering emulsion stabilised by spiropyran-decorated nanoparticles.…”