Clara Pereira - Naphthopyran-Based Silica Nanoparticles as New High-Performance Photoresponsive Materials

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        “Naphthopyran-Based Silica Nanoparticles as New High-Performance   Photoresponsive Materials”,Tânia   V. Pinto,    Paula Costa,    Céu M. Sousa,    Carlos A. D. Sousa,    Andreia Monteiro,    Clara Pereira*,Olívia   Salomé G. P. Soares,    Carla S. M. Silva,    Manuel Fernando R. Pereira,    Paulo J. Coelho, Cristina Freire,   ACS Applied Materials & Interfaces   2016,   8, 7221–7231. DOI:   10.1021/acsami.5b11983

        *Corresponding author

      Abstract:

      Hybrid nanomaterials based on the covalent grafting of silylated   naphthopyrans (NPTs) onto silica nanoparticles (SiO2  NPs) were successfully prepared and studied as new photochromic   materials. They were prepared by a two-step protocol consisting   of (i) NPTs (derivatives from 2H-naphtho[1,2-b]pyran   (2H-NPT) and 3H-naphtho[2,1-b]pyran   (3H-NPT)) silylation by a microwave-assisted reaction   between hydroxyl-substituted NPTs and 3-(triethoxysilyl)propyl   isocyanate, followed by (ii) covalent post-grafting onto   SiO2 NPs. In order to study the role of the silylation   step, the analogous non-silylated nanomaterials were also   prepared by direct adsorption of NPTs. The characterization   techniques confirmed the successful NPTs silylation and   subsequent grafting to SiO2 NPs. All   SiO2-based nanomaterials revealed photoswitching   behavior, following a biexponential decay. The SiO2  NPs functionalized with silylated 3H-NPTs   (SiO2@S3 and   SiO2@S4) presented the most promising   photochromic properties, showing fast coloration/decoloration   kinetics (coloring in 1 min under UV irradiation and fading in   only 2 min) and high values of total color difference   (ΔE*ab = 30–50). Also, the   2H-NPTs-based SiO2 NPs   (SiO2@S1 and   SiO2@S2) presented fast coloration   and good color contrasts (ΔE*ab = 54), but   slower fading kinetic rates, taking more than 2 h to return to   their initial color. In contrast, the SiO2 NPs   functionalized with non-silylated NPTs   (SiO2@1 and   SiO2@3) showed weaker color contrasts   (ΔE*ab = 6–10) and slower fading kinetics,   proving that the NPT silylation step was crucial to enhance the   photochromic behavior of SiO2 NPs based on NPTs.   Furthermore, the silylated-based nanomaterials showed good   photostability upon prolonged UV light exposure, keeping their   photochromic performance unchanged for at least 12 successive   UV/dark cycles, anticipating interesting technological   applications in several areas.

      Address (URL): http://dx.doi.org/10.1021/acsami.5b11983