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Tumor-selective photodynamic therapy is a successful method for ablation of malignant and cancerous cells. Herein, we introduce the design and preparation of functionalized acrylic copolymer nanoparticles with spiropyran (SP) and imidazole groups through a facile semicontinuous emulsion polymerization. Then, Au ions were immobilized and reduced on their surface to obtain photoresponsive gold-decorated polymer nanoparticles (PGPNPs). The prepared PGPNPs were surface-modified with folic acid as a site-specific tumor cell targeting agent and improve intracellular uptake via endocytosis. Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy analyses, UV-vis spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy images were employed to characterize their spectral and morphological properties. Fluorescence microscopy images and inductively coupled plasma analysis demonstrated the cell line labeling capability and improved targeting efficiency of folate-conjugated PGPNPs (FA-PGPNPs) toward rat brain cancer cells (C6 glioma) with 71.8% cell uptake in comparison with 28.8% for the nonconjugated ones. Nonpolar SP groups are converted to zwitterionic merocyanine isomers under UV irradiation at 365 nm and their conjugation with Au nanoparticles exhibited enhanced photogeneration of reactive oxygen species (ROS). These were confirmed by intracellular ROS analysis and cytotoxicity evaluation on malignant C6 glioma cells. Owing to the strong surface plasmon resonance absorption of gold nanoparticles, FA-PGPNPs provided elevated local photothermal efficiency under near-IR irradiation at 808 nm. The prepared multifunctional FA-PGPNPs with a comprehensive integration of prospective materials introduced promising nanoprobes with targeting ability, enhanced tumor photodynamic therapy, cell tracking, and photothermal therapy.

Covalent bonding of photochromic molecules to a polymer matrix, flexibility of the polymeric host, and also its nanofibrous state are appropriate conditions to enhance the switching rate, photofatigue resistance, sensitivity, and long-term performance of these photo-active groups. Herein, photoresponsive polymethyl methacrylate and poly(methyl methacrylate-cobutyl acrylate) chemically modified with spiropyran (MSP and MBSP, respectively) were prepared through emulsion polymerization. To improve photosensitivity and reduce response time, the corresponding nanofibers (MSP@NF and MBSP@NF) were prepared by an electrospinning technique. Smooth and beadless morphology, high porosity (above 85%), and uniform diameter size distribution of MSP@NF (169 ± 39 nm) and MBSP@NF (203 ± 47 nm) were identified. Time-dependent UV−vis spectra and photo-isomerization kinetics revealed that flexible MBSP@NF has remarkable enhancement in the SP to merocyanine isomerization rate (19 folds) relative to the corresponding film. Reversible responsivity to HCl and ammonia vapors showed a dramatic color change and maximum absorption peak displacement for nanofiber samples immediately, together with fluorescence switching "on" and "off", while this took about 10 min for the MBSP@F sample. This was attributed to the high surface area and porous structure of these nanofibers, providing enhanced diffusion and interaction with the photo-active groups. Reversible optical write−erase cycles with improved response time and color intensity approved photopatterning capability of MBSP@NF. Enhanced photochemical, photostability, and photofatigue resistance of MBSP@NF within 10 cycles of alternating exposure to HCl−ammonia vapors and also UV−vis irradiations revealed the potentiality of such nanofibers in visual reversible photopatterning and optochemical acidochromic and ammonia-chromic portable probes.

Exploitation of a polymer carrier for introducing photochromic properties to cellulose matrix has several advantages such as photostability, photoreversibility, elimination of dye aggregation, and elimination of undesirable negative photochromism. The switching rate of a photochromic compound in the polymer matrix depends on steric restrictions, polarity, protic characteristics, and flexibility of the surrounding media. Here, the copolymerization of a spiropyran-based monomer with butyl acrylate and methyl methacrylate comonomers is reported through semicontinuous emulsion polymerization and the kinetics of isomerization and switching rate are investigated. The obtained latex was incorporated into cellulosic paper through chemical modification. The analysis confirmed a ring-opening reaction between hydroxyl groups in cellulose and epoxy functional groups in the low T g latex. Morphological studies and contact angle measurements demonstrated an improved uniformity and enhanced hydrophobicity in the modified cellulose. Solid state UV−vis spectroscopy was employed to determinate the switching rate, kinetics analyses, maximum reflection wavelengths, and removal of undesired negative photochromism. Analyses revealed that flexible epoxy-functionalized photochromic modified cellulose exhibited reasonable fatigue resistance, photoresponsivity, and photoreversibility upon alternative UV and visible irradiation.

Incorporation of chromophores into a polymer chain results in prominent photoreversibility and fatigue resistance, photostability over the long term, and restriction of the internal conversion (IC). Here, we report the copolymerization of two photoactive monomers with methyl methacrylate via emulsion polymerization in order to obtain photoswitchable dual-color fluorescent nanoparticles. For this purpose, azocarbazole ethyl acrylate (AzoCzEA) and spiropyran ethyl acrylate (SPEA) were synthesized and the fluorescence polymeric latex nanoparticles were prepared correspondingly. FT-IR and 1 HNMR spectra were used to confirm the structure of novel fluorescent AzoCzEA. UV−vis studies of the obtained nanoparticles displayed the spectral features of both AzoCzEA and SPEA under stimuli-irradiation and inclusion of these chromophores into the polymer particles. DSC analysis revealed an increase in T g of the prepared copolymer, indicating covalently incorporation of the photoactive monomers into the polymer chains. The optimum ratio of two chromophores to achieve complete quenching and highest energy transfer was determined by UV−vis spectroscopy. DLS and SEM results demonstrated particle size distribution of 40−80 nm with spherical morphology. Fluorescence spectra revealed remarkable fluorescence resonance energy transfer (FRET) from AzoCzEA to SPEA after UV irradiation at 365 nm and dual-color characteristic of the prepared nanoparticles. Besides, an enhancement in the photoreversibility, photostability, prevention of IC, dye leakage, and aggregation were studied elaborately. The obtained results were attributed to the involvement of such chromophores into the polymeric matrix via covalent bonding. Labeling and tracking of living cells and rewriteable patterning are potential applications for such dual-color fluorescent nanoparticles.

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