Guang Wang

The high stability of merocyanine and significant slow fading speed of naphthopyran in layer-by-layer assembled films via hydrogen bonding

A photochromic polymer film has been fabricated by the layer-by-layer (LBL) self-assembly through alternating the deposition of poly(acrylic acid) bearing a naphthopyran copolymer and poly(4-vinylpyridine) in an organic solvent. The multilayer assembly process is monitored via UV-vis spectroscopy by measuring the increase in absorbance at 380 nm, and the results reveal that the multilayer films grow in a uniform way in each deposition. Atomic force microscopy (AFM) images prove that the surface of the film was relatively smooth. The photochromic properties of the naphthopyran in the LBL films are investigated and the kinetic results confirm that the colored merocyanine in the LBL films show a significant slow fading speed (critical T1/2 decoloration time increased to 64 min in the 3-bilayer film) and are more stable than those in previous reports.

Toward modulation of the naphthopyran photochromism: a miniemulsion copolymerization strategy

Novel naphthopyran derivative based photochromic polymer nanoparticles are prepared via miniemulsion copolymerization with methyl methacrylate (MMA) and n-butyl methacrylate (BMA) monomers. The systematic modulation of the photochromic rate can be achieved via tuning the ratio of MMA and BMA monomers to lead the naphthopyrans to swing between rigid and soft surroundings. Transmission electron micrographs (TEM) and dynamic light scattering (DLS) images prove that the nanoparticles are discrete and smooth. The typical spectral characteristics of naphthopyran in the polymer nanoparticles indicate that the photochrome is incorporated into the nanoparticles successfully. In addition, the polymer nanoparticles exhibit good photochromic reversibility and stability upon UV irradiation and thermal back reaction.

Ultrasensitive and highly selective detection of Cu2 + ions based on a new carbazole-Schiff

A new chemosensor for Cu2+ based on Schiff base with high sensitivity and selectivity was designed and synthesized. The fluorescence intensity of the chemosensor in CH3CN solution was enhanced 160-fold after the addition of 10 equiv. Cu2+ over other metal ions. In addition, it also facilitates colorimetric detection for Cu2+ in CH3CN solution. The chemosensor displayed low detection limit and fast response time to Cu2+.

Preparation and photochromic properties of layer-by-layer self-assembly films and light-responsive micelles based on amphiphilic naphthopyran derivative

An amphiphilic naphthopyran derivative (DSNP) with negative-charged di-sulfatoethoxy was first designed and synthesized. DSNP was used to prepare the LBL self-assembly films with cationic quaternized poly(4-vinylpyridine) (P4VPQ). The multilayer assembly process was monitored via UV-Vis spectra and the DSNP displayed a significant slow fading rate in film. In addition, DSNP was also used as the light-responsive group to fabricate light-responsive micelles with polyethylene glycol-triethylamine bromide (PEG-NEt3). The photoisomerization of naphthopyran moieties can rapidly and reversibly tune the disassembly and re-assembly of the micelles. The changes of fluorescent spectra of Nile Red (NR) in water solution of polymeric micelles demonstrated that the polymeric micelle can be used as nanocarriers to encapsulate, release and re-encapsulate guest solutes on demand controlling of light irradiation. The results indicate that the amphiphilic naphthopyran can be used in both optical-switches and biomedical area for drug delivery.

Light-triggered “on–off” switching of fluorescence based on a naphthopyran-containing compound polymer micelle

We report a compound polymer micelle with light-triggered “on–off” switching of fluorescence based on the self-assembly of two block copolymers. First, the naphthalimide fluorophore is incorporated into poly(styrene-stat-naphthalimide)-b-poly(N-isopropyl acrylamide) [P(St-stat-MANI)-b-PNIPAM]. Second, the naphthopyran unit is engineered in poly(styrene-stat-naphthopyran)-b-poly(N-isopropyl acrylamide) [P(St-stat-NP)-b-PNIPAM] to manipulate the fluorescence when self-assembled into compound micelles with fluorophore-containing P(St-stat-MANI)-b-PNIPAM. The fluorescence of naphthalimide (MANI) can be modulated between “on” and “off” states by the photochromic reaction of naphthopyran (NP) upon UV irradiation and thermal fading reaction. Furthermore, Nile red (NR) was encapsulated in the micelle and showed a controlled release behavior by light. Our strategy may be extended for designing a range of multifunctional smart fluorescent materials such as chemical sensors.

New selective “on-off” fluorescence chemosensor based on carbazole Schiff base for Fe 3+ detection

A new double Schiff base, carbazole, and diaminomaleonitrile-based chemosensor for Fe3+ with high sensitivity and selectivity was designed and synthesized. Addition of only Fe3+ ions induced the fluorescence quenching of the chemosensor in DMF solution. The chemosensor formed a 1:1 complex with Fe3+ with the high binding constant of 7.98·10–6 M–1. The chemosensor displayed low detection limit (3.75·10–8 M) and fast response time (15 s) to Fe3+.

A new high selective and sensitive turn-on fluorescent and ratiometric absorption chemosensor for Cu 2+ based on benzimidazole in aqueous solution and its application in live cell

A new benzimidazole base turn-on fluorescent and ratiometric absorption chemosensor (L) bearing bidentate ligand for detection of Cu2+ was designed and synthesized. Fluorescence and UV-vis spectra studies demonstrated that L can detect Cu2+ ions in aqueous solution using fluorescence enhancement and ratiometric absorption sensing over a wide pH range. Both fluorescent and ratiometric absorption sensing of L for Cu2+ possessed high selectivity and sensitivity over other competitive metal ions and had low detection limit. Jobs plot, mass spectra and DFT calculation indicated the sensing mechanism is the complex formation between L and Cu2+ with 1:2 stoichiometry. Fluorescence images of HepG2 in the absence and presence of Cu2+ displayed L had cell permeability and detection ability for Cu2+ in live cells.