Ming Jin

π-conjugated sulfonium-based photoacid generators: an integrated molecular approach for efficient one and two-photon polymerization

The cationic photoinitiating abilities of a series of ‘push–pull’ sulfonium-based photoacid generators (PAGs) have been investigated. In this linear π-conjugated series, a 4-N,N-diphenylaminostilbene subunit is associated with different types of sulfonium substituents, which are connected to the stilbene moiety either in the 4′ position or in the 3′ position. This para-to-meta substitution effect leads to a strong increase of the quantum yield for acid generation with a maximum value of ca. 0.5. Such a positioning effect has a strong influence on the efficiency of the S–C bond cleavage. A detailed photolysis mechanism has been proposed. In contrast to commercially available sulfonium salts, these highly reactive π-conjugated PAGs all exhibit large absorption in the visible range as well as large two-photon absorption cross-sections (δmax > 600 GM) in the near-infrared region. As a consequence, efficient one and two-photon polymerization reactions are observed at 405 nm and 800 nm, respectively, using typical monomers such as cyclohexene oxide, n-butyl vinyl ether or SU-8 photoresists. By the fabrication of well resolved two-dimensional microstructures, we finally demonstrate the potential use of these new generation PAGs in the fields of one and two-photon lithography.

Design of D–π–A type photoacid generators for high efficiency excitation at 405 nm and 800 nm

New sulfonium salts with diphenylamino asymmetrically substituted stilbene as a D-π-A conjugated system have been synthesized. The resulting photoacid generators exhibit a highly efficient acid photogeneration process by either one-photon 405 nm or two-photon 800 nm excitation.

Two-photon absorption and polymerization ability of intramolecular energy transfer based photoinitiating systems.

We design a new photoinitiating system where the two-photon absorption of a 2,7 bisaminofluorene moiety leads to the photoactivation of a camphorquinone subunit through a Förster-type intramolecular energy transfer: the application to a two-photon polymerization reaction is demonstrated.

Supramolecular Nanoparticles via Single-Chain Folding Driven by Ferrous Ions

Single-chain nanoparticles can be obtained via single-chain folding assisted by intramolecular crosslinking reversibly or irreversibly. Single-chain folding is also an efficient route to simulate biomacromolecules. In present study, poly(N-hydroxyethylacrylamide-co-4-(propoxy urethane ethyl acrylate)-2,2:6,2-terpyridine) (P(HEAm-co-EMA-Tpy)) is synthesized via reversible addition fragmentation chain transfer polymerization. Single-chain folding and intramolecular crosslinking of P(HEAm-co-EMA-Tpy) are achieved via metal coordination chemistry. The intramolecular interaction is characterized on ultraviolet/visible spectrophotometer (UV-vis spectroscopy), proton nuclear magnetic resonance ((1)H NMR), and differential scanning calorimetry (DSC). The supramolecular crosslinking mediated by Fe(2+) plays an important role in the intramolecular collapsing of the single-chain and the formation of the nanoparticles. The size and morphology of the nanoparticles can be controlled reversibly via metal coordination chemistry, which can be characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic force microscope (AFM).

Two-photon lithography in visible and NIR ranges using multibranched-based sensitizers for efficient acid generation

We investigated methodically the one- and two-photon absorption properties of a series of multibranched triphenylamine-based chromophores incorporating 4-(methylthio)styryl fragments as external substituents. Some relevant structure–property relationships relative to these highly fluorescent compounds have been derived based on emission anisotropy measurements, quantum chemical calculations and the use of the exciton coupling theory. Even though branching effects lead to a cooperative enhancement of the two-photon absorption (2PA), all compounds exhibit relatively low-to-moderate 2PA cross-sections (δ ≤ 100 GM) in the NIR region. However, the ‘so-called’ one-photon resonance enhancement effect leads to a remarkable increase of δ by more than one order of magnitude in the visible range. This strong 2PA ability has been associated with an efficient photosensitization of iodonium salt to elaborate a new bicomponent photoacid generator, which is readily two-photon activable at 532 nm. In the visible range, the strong enhancement of the efficiency of the two-photon induced polymerization is clearly demonstrated as compared with that observed in the NIR region.

One-pot synthesis of porous monolith-supported gold nanoparticles as an effective recyclable catalyst

Gold nanoparticles (AuNPs) are excellent catalysts, but their recycling remains a central concern. Support of AuNPs on a porous monolith is one popular strategy but it usually suffers from multistep and inefficient preparation. Herein, we show a one-pot strategy to recyclable AuNPs supported on a porous monolith. It is known that the polymerization of the oil phase of a high internal phase emulsion (HIPE), stabilized by surfactants, can lead to a macroscopic and porous monolith (polyHIPE). If the surfactant is replaced with a dendritic amphiphile (DA) of PEI@PS (hyperbranched polyethylenimine (PEI) functionalized with polystyrene (PS) and dodecyls), and the water phase is charged with chloroauric acid, then the one-pot fabrication of AuNP-decorated polyHIPE (Au-DA-polyHIPE) is feasible. Alternatively, if Au-DA (AuNP stabilized with PEI@PS) is used instead of the surfactants, then Au-DA-polyHIPE can be similarly obtained. The Au-DA-polyHIPE samples have open-cell and porous structure, and can effectively catalyze the reduction of 4-nitrophenol. The catalytic materials are recyclable without any decrease in activity, at least within 6 cycles, in which the multivalent and multi-ligand PEI should be responsible for the stability.

Dendritic amphiphile mediated porous monolith for eliminating organic micropollutants from water

Few adsorbents with a macroscopic size can combine well with a 3D microscopically well-tailored surface. Herein, we show that a dendritic amphiphile can directly lead to such an adsorbent, which can simultaneously eliminate anionic dyes, anionic surfactants and hydrophobic polycyclic aromatic hydrocarbons (PAHs) from water.

Dendritic Amphiphile Mediated One-Pot Preparation of 3D Pt Nanoparticles-Decorated PolyHIPE as a Durable and Well-Recyclable Catalyst

Straightforward organization of platinum nanoparticles (PtNPs) onto a macroscopic and robust material is described. PtNPs are in situ produced and stabilized by a dendritic amphiphile, where the latter consists of a hyperbranched polyethylenimine (PEI) as core and poly(styrene-co-2-ethylhexyl acrylate (P(St-EHA)) as shell. The resulting Pt@PEI@P(St-EHA), upon mixing with biphasic water and oil (a mixture of EHA and a dimethacrylate cross-linker in toluene), can self-assemble along the water/oil (W/O) interface and result in a stable emulsion. At W/O = 80/20 (volume ratio), a high internal phase emulsion (HIPE) forms and can be radically transformed into an open-cellular and elastic monolith termed Pt-polyHIPE, with PtNPs decorated on the surface. The Pt-polyHIPE is mechanically robust, and the cross-linking homogeneity by the dimethacrylate is responsible for the strength. The Pt-polyHIPE shows an active catalytic property, as evaluated by reduction of 4-nitrophenol. The material is conveniently and well recyclable, showing no decrease in catalytic activity at least within 20 cycles. Energy-dispersive X-ray spectra and thermogravimetric analysis also support sufficient retaining of the Pt species, where the multivalent and multiligand PEI should be responsible for this property.

One/two-photon-sensitive photoacid generators based on benzene oligomer-containing D–π–A-type aryl dialkylsulfonium salts

Novel sulfonium-based D–π–A photoacid generators (PAGs) with a benzene oligomer (from one to four) as a π-conjugated system that are highly photosensitive in the near-ultraviolet region (365 nm) were prepared. The maximum absorption and molar extinction coefficients of the PAGs redshifted and enhanced with the increasing length of the conjugated systems. The quantum yields of PAGs were high (three of them were over 0.6) and improved by adjusting the number of the phenyl rings. The quantum chemical calculation results proved that the molecular configuration and nature of the frontier orbitals are crucial factors which affect PAG performance. Photopolymerization kinetic results demonstrated that these sulfonium-based PAGs were highly efficient cationic photoinitiators, and the i-line sensitivities were evaluated based on the photolithographic performance of the PAG-containing SU-8 resins. In addition, the two-photon absorption cross sections (δ700 nm > 400 GM) matched the requirements needed in the 3D fabrication of polymer microstructures.

A multifunctional azobenzene-based polymeric adsorbent for effective water remediation

The efficient removal of trace carcinogenic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and ionic dyes, from water is an important technical challenge. We report a highly effective recyclable multifunctional azobenzene (AZ)-based silica-supported polymeric adsorbent which can simultaneously remove both PAHs and anionic dyes from water to below parts per billion (ppb) level based on multiple interactions such as the hydrophobic effect, π–π stacking and electrostatic interactions, thus providing a new strategy for designer water remediation materials.