Abstract
The possibility of incorporating functional groups into molecular photoswitches is a prerequisite for their versatility and broad-range applications. Herein, we present the first successful synthesis of donor–acceptor Stenhouse adducts (DASA) chromophores featuring a thiol group. The latter provides a unique opportunity to investigate the photoswitching behavior of these visible-light operating chromophores on the surface of metallic nanoparticles. This behavior can be modulated by irradiation time, solvent composition, DASA population, and the organic layer underneath the chromophore. Moreover, the changes in polarity induced by DASA photoisomerization are translated onto the colloidal particles, giving rise to unusual interfacial and bulk-phase phenomena, including nonlinear solubility effects and reversible agglomeration that takes place in a time-controllable manner. These findings pave the way for the rational design of new photoresponsive and smart materials.
Highlights
Donor−acceptor Stenhouse adducts (DASAs) are arguably one of the most promising photoswitches synthesized recently.[34−40] The advantage of donor−acceptor Stenhouse adducts (DASA), apart from the negative photochromism, is that the isomerization is accompanied by large conformation and polarity changes, where a neutral less polar linear isomer is transformed into a charged more polar cyclic form[41] with visible light and reverted upon thermal equilibration in the dark
We resorted to a simpler method of calculating half-width at half-maximum (HWHM) of plasmon band, which may serve as an illustrative parameter of aggregation
We thought that the reason for the failure with the synthesis of thiolated DASAs could be the competition of thiol group for the ring opening of activated furan. 1H NMR experiments with model 1-octanthiol, showed that no reaction occurred on the timescale of DASA formation, which was consistent with the report of Read de Alaniz et al.[53]
Summary
The photoisomerization of organic chromophores is an elegant means to reversibly manipulate the property of matter with spatiotemporal precision and without the generation of chemical wastes.[1−9] Light-triggered reaction cascades occurring within living cells regulate ion transport in bacteria[10−12] and provide animal vision.[13,14] Similar mechanisms are implemented by humans for creating smart functional materials[15−19] and catalytic systems.[20−22] To this end, artificial photoswitches responding to specific wavelengths of electromagnetic radiation are being continually designed.[23−32] The most demanded photoswitches are nowadays those operating in the visible light due to little harm it exerts to organic and biomolecules.[33]. Since DASA ligand absorption bands overlap nanoparticles plasmon band, it is not possible to apply the Mie and Gans model to calculate the precise aggregation degree of nanoparticles.[51] we resorted to a simpler method of calculating half-width at half-maximum (HWHM) of plasmon band, which may serve as an illustrative parameter of aggregation Aggregated nanoparticles have their plasmon band red-shifted due to decreased interparticle distance and resulting plasmon coupling.[52] overlapping of the shifted plasmon band with the original one will be seen as a “broadened” band, which constitutes a basis for the use of the HWHM parameter as a benchmark for aggregation. The sample was kept in the dark, and DLS measurements were taken again
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