title: 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.
authors.affiliation: REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , 4169-007 Porto, Portugal.
authors.forename: Tânia V
authors.initials: TV
authors.lastname: Pinto
authors.affiliation: REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , 4169-007 Porto, Portugal.
authors.forename: Paula
authors.initials: P
authors.lastname: Costa
authors.affiliation: Departamento de Química e CQ-VR, Universidade de Trás-os-Montes e Alto Douro , 5001-801 Vila Real, Portugal.
authors.forename: Céu M
authors.initials: CM
authors.lastname: Sousa
authors.affiliation: REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , 4169-007 Porto, Portugal.
authors.forename: Carlos A D
authors.initials: CA
authors.lastname: Sousa
authors.affiliation: CeNTI, Centro de Nanotecnologia e Materiais Técnicos, Funcionais e Inteligentes , 4760-034 Vila Nova de Famalicão, Portugal.
authors.forename: Andreia
authors.initials: A
authors.lastname: Monteiro
authors.affiliation: REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , 4169-007 Porto, Portugal.
authors.forename: Clara
authors.initials: C
authors.lastname: Pereira
authors.affiliation: Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE-LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto , 4200-465 Porto, Portugal.
authors.forename: Olívia Salomé G P
authors.initials: OS
authors.lastname: Soares
authors.affiliation: CeNTI, Centro de Nanotecnologia e Materiais Técnicos, Funcionais e Inteligentes , 4760-034 Vila Nova de Famalicão, Portugal.
authors.forename: Carla S M
authors.initials: CS
authors.lastname: Silva
authors.affiliation: Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE-LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto , 4200-465 Porto, Portugal.
authors.forename: Manuel Fernando R
authors.initials: MF
authors.lastname: Pereira
authors.affiliation: Departamento de Química e CQ-VR, Universidade de Trás-os-Montes e Alto Douro , 5001-801 Vila Real, Portugal.
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Coelho
authors.affiliation: REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , 4169-007 Porto, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Freire
keywords: naphthopyrans; photochromism; photoresponsive materials; photostability; silica nanoparticles; silylation