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


      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.

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