Spiropyran Photoisomerization Dynamics in Multiresponsive Hydrogels

Abstract

Light-responsive, spiropyran-functionalized hydrogels have been used to create reversibly photoactuated structures for applications ranging from microfluidics to nonlinear optics. Tailoring a spiropyran-functionalized hydrogel system for a particular application requires an understanding of how co-monomer composition affects the switching dynamics of the spiropyran chromophore. Such gels are frequently designed to be responsive to different stimuli such as light, temperature, and pH. The coupling of these influences can significantly alter spiropyran behavior in ways not currently well understood. To better understand the influence of responsive co-monomers on the spiropyran isomerization dynamics, we use UV−vis spectroscopy and time-dependent fluorescence intensity measurements to study spiropyran-modified hydrogels polymerized from four common hydrogel precursors of different pH and temperature responsivity: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate. In acidic and neutral gels, we observe unusual nonmonotonic, triexponential fluorescence dynamics under 405 nm irradiation that cannot be explicated by either the established spiropyran−merocyanine interconversion model or hydrolysis. To explain these results, we introduce an analytical model of spiropyran interconversions that includes H-aggregated merocyanine and its light-triggered disaggregation under 405 nm irradiation. This model provides an excellent fit to the observed fluorescence dynamics and elucidates exactly how creating an acidic internal gel environment promotes the fast and complete conversion of the hydrophilic merocyanine speciesto the hydrophobic spiropyran form, which is desired in most light-sensitive hydrogel actuators. This can be achieved by incorporating acrylic acid monomers and by minimizing the aggregate concentration. Beyond spiropyranfunctionalized gel actuators, these conclusions are particularly critical for nonlinear optical computing applications.

Regulation of Bacterial Behavior by Light and Magnetism Mediated by Mesoporous Silica-Coated MnFe2O4@CoFe2O4 Nanoparticles

“…To endow light/magnetism dual responsiveness of the regulation system, magnetic MSNs with the core–shell structure were synthesized and further modified by the photoactive molecule SP (Scheme ). The magnetic core (MnFe 2 O 4 @CoFe 2 O 4 ) was first synthesized by the thermal decomposition method. , TEM observation showed that the obtained magnetic core had round morphology with the average size of 12.6 nm (Figure S1a,b). The magnetization curve revealed that the magnetic cores had a saturation magnetization of 89 emu/g and exhibited no hysteresis loop (Figure S1c), suggesting that they were superparamagnetic nanoparticles. , AMF heating assays further showed that the temperature of the magnetic cores rapidly increased from 25 to >50 °C after 300 s of AMF stimulus (375 kHz, 5 kW) and then tended to be stable, with the specific loss power (SLP) of 910 W/g (Figure S1d), suggesting high AMF-heating capacity of the magnetic core.…”

Toward real-world applications: promoting fast and efficient photoswitching in the solid state

“…coupling, condensation) with already formed polymers with functional groups. 134 Leng and coworkers fabricated shape memory polymeric materials by grafting SP on the side chain of polyurethane. The SP exhibited fast SC-to-MC isomerization under UV light irradiation.…”

Touch-Responsive Hydrogel for Biomimetic Flytrap-Like Soft Actuator

“…Stimuli-responsive hydrogels, which are capable of changing their physicochemical properties in response to the specific external stimulus, are deemed to be one of the most important building blocks of the next-generation advanced technologies and intelligence devices [8][9][10]. Over the past decade of booming development, various kinds of smart hydrogels with stimuli responsiveness have been developed by modifying stimuli-responsive polymers [11][12][13], introducing functional additives [14][15][16] and designing ingenious structures [17][18][19]. At this stage, the stimuli-responsive smart hydrogels show multi-type changes in size, shape, optical properties, mechanical properties and electric properties adapting to various external stimuli [20][21][22][23][24][25][26][27], and they have been widely applied in soft actuators [5,[28][29][30] and other intelligence areas [31][32][33][34][35][36][37][38].…”