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

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.

A Multi‐Functional and Rapid Responsive Photochromic Hydrogel for UV Indicators

“…2,2‐diphenyl‐2H‐naphtho[1,2‐b] pyran‐6‐carbaldehyde (NP) synthesis is based on previous literature. [ 7 ] The specific synthesis procedures are as follows: the 4‐hydroxy‐1‐naphthaldehyde (2 g), 1,1‐diphenylprop‐2‐yn‐1‐ol (2.6608 g), and p‐toluenesulfonic acid (APTS) (372 mg) were dissolved in 40 mL chloroform, and heated at 60 °C for 1 h. The resulting mixture was cooled to room temperature and distilled to remove the solvent. The solid product was collected by filtering and washing with diethyl ether.…”

“…[ 4–6 ] Therefore, ultraviolet prediction, real‐time monitoring, and protection provide a vital effect on numerous aspects of human health. Owing to the fact that photochromic materials are capable of producing reversible color changes when excited by electromagnetic radiation (ultraviolet, visible, or infrared, [ 7–8 ] therefore, the photochromic material that can be excited by ultraviolet light has become a superb candidate for the detection and protection of ultraviolet rays. Since the inception of studies on photochromic materials, they have been widely applied in information storage, anti‐counterfeiting, display, molecular switches, photochromic windows, photochromic decorations, photochromic ophthalmic lenses, light printing, and other aspects.…”

Triethylamine‐Mediated One‐Pot Synthesis of Benzo[f]chromene Derivatives

“…Since then, the scaffolds are used for making ophthalmic lenses with high color ability and rapid color reversibility; also employed in temporary or permanent memories, electronic display systems and optical switches etc . Silica‐based nanoparticles with silylated benzo[ f ]chromene derivatives are promising photochromic nanomaterials having fast coloration and higher optical properties …”

Highly active organosulfonic aryl-silica nanoparticles as efficient catalysts for biomass derived biodiesel and fuel additives

“…The parent SiO 2 NPs, SiO 2 NPs_10 and SiO 2 NPs_100, were exhaustively characterized in previous reports by several techniques (SEM, TEM and FTIR) [34][35][36]. The TEM and SEM micrographs of the SiO 2 NPs_10 and SiO 2 NPs_100, respectively, revealed uniform spheres with an average particle size of 123 ± 7 nm and 15 ± 3 nm, and narrow size distributions [35,36]. Upon organosulfonic-functionalization of the SiO 2 NPs_100 with different alkyl and aryl-organosilanes no significant morphological changes were observed [34].…”