Electrospinning Machine | Engineering covalent core-shell architectures for dynamic optical cryptography: Time-resolved dual switching in organometallosilica nanocomposites

Dynamic optical encryption technology faces increasing demands for enhanced security, reversibility, and improved multidimensional response capabilities. Traditional systems rely on static luminescent labels or monochromatic "on-off" switching, exhibiting significant limitations including susceptibility to replication, vulnerability to environmental interference, and overly simplistic encryption logic. Research indicates that platinum(II) complexes, due to their advantages such as tunable luminescence wavelength, concentration-dependent self-assembly characteristics, and high quantum yield, have become highly promising functional materials (Na. Commun., 2025, 16, 1971; Chin. Chem. Lett. 2025, 36, 110735; Chin. Chem. Lett. 2024, 35, 109585; Sci. China Chem. 2023, 66, 2878; A CIE 2022, 61, e202210703; JACS 2021, 143, 21676; JACS 2021, 143, 10659; PNAS 2019, 116, 13856). On the other hand, the classic photochromic molecule spiropyran (SP) can achieve reversible fluorescence switching between the closed SP state and the open merocyanine (MC) state isomerization driven by UV/visible light (Chem. Eng. J. 2024, 497, 154274; Adv. Opt. Mater. 2023, 11, 2301047; Chem. Eng. J. 2022, 450, 138390;). However, efficient SP isomerization requires sufficient spatial freedom, while in rigid matrices, this process is significantly inhibited, leading to decreased luminescence switching efficiency.

Recently, Professor Li Yongguang's team at Hangzhou Normal University published their latest research, "Engineering covalent core-shell architectures for dynamic optical cryptography: Time-resolved dual switching in organometallosilica nanocomposites," in the journal Chemical Engineering Journal. The researchers proposed a covalent bonding strategy to construct a core-shell structured organometallo-silica nanocomposite, achieving dual-wavelength dynamic luminescence switching. This design not only provides the necessary local free volume for SP ↔ MC isomerization but also effectively prevents molecular leaching through covalent bonding, thereby ensuring the material's optical stability in complex environments. Furthermore, they successfully prepared nanofiber membranes with dynamic multi-color luminescence characteristics via electrospinning technology, offering an innovative solution for flexible anti-counterfeiting and multi-level information storage (Figure 1).

Figure 1 Schematic diagram of the synthesis process and application of the Pt-SiO2@SP-SiO2 composite material.

Figure 2 Structure and morphology characterization of SiO2, Pt-SiO2, and Pt-SiO2@SP-SiO2 nanocomposites.

The Pt-SiO2@SP-SiO2 composite material was prepared via a two-step co-condensation method. FT-IR confirmed the successful covalent grafting of the platinum(II) complex and SP onto the silica framework while preserving their molecular structures. XRD indicated that both chromophores are in an amorphous state within the silica framework, further demonstrating that the high surface area and spherical three-dimensional framework of SiO2 promote a loose spatial distribution of SP molecules, providing the necessary free volume for their photoisomerization (Figure 2 A-C). SEM and DLS showed that the Pt-SiO2@SP-SiO2 composite material has a core diameter of 147.7 nm and a shell thickness of 42.8 nm (Figure 2 D-I).

Figure 3 Morphology and non-leaching characteristics of the Pt-SiO2@SP-SiO2 material.

High-resolution SEM and TEM clearly revealed the core-shell interface, further confirming the composite material possesses a core-shell structure (Figure 3 A-D). Comparison with a control sample (SP/Pt-SiO₂) prepared by physical adsorption revealed that the Pt-SiO2@SP-SiO2 composite material maintains good optical activity under continuous erosion by organic reagents, demonstrating that the covalent bonding strategy effectively enhances the stability of the chromophores (Figure 3 E-G).

Figure 4 Time-resolved emission spectra and reversible photochromic behavior of composites with different Pt/SP molar ratios. 

Under ultraviolet light (365 nm) irradiation, the composite material's photochromic switching characteristics are pronounced: the apparent color gradually transitions from pale yellow (SP state) to purple (MC state), and the luminescence color evolves from green (initial Pt-dominated emission) to red (MC-dominated emission). Furthermore, it completely reverts to the initial state under visible light (520 nm) irradiation.

Figure 5 Preparation of Pt-SiO2@SP-SiO2/PUA electrospun membrane and its application in rewritable information.

Figure 6 Multifunctional anti-counterfeiting application of the Pt-SiO2@SP-SiO2/PUA electrospun membrane.

By incorporating the Pt-SiO2@SP-SiO2 composite material into a polymer matrix (PUA) via the electrospinning process, large-area flexible films can be prepared. The nanofiber films retained the photophysical properties of the Pt-SiO2@SP-SiO2 composite and exhibited robust reversible cyclability within 10 switching cycles under alternating UV/visible light irradiation (Figure 5). Based on the dynamic multi-color luminescence and programmable photochromic characteristics of the Pt-SiO2@SP-SiO2/PUA film, the researchers developed a multi-level anti-counterfeiting system that integrates information encryption, authentication, and erasure functions within a single platform (Figure 6). The Pt-SiO2@SP-SiO2/PUA film provides new ideas for the preparation of advanced anti-counterfeiting materials in the fields of high-security documents and intelligent packaging.

Paper link: https://doi.org/10.1016/j.cej.2025.167799