Inhibition and enhancement of the fluorescence from embedded fluorescent defects in colloidal crystals (CCs) is demonstrated. The embedded defects, which are verified by the passbands and scanning electron microscope images, are fabricated inside the CCs by employing two-photon polymerization of allyl-fluorescein (allyl-FL) doped photoresist. The fluorescence image is indistinct when the photoluminescence band of allyl-FL locates at the photonic stopband. However, a bright fluorescence image is observed when the photoluminescence band is located at the photonic stopband edge. The inhibition and enhancement in fluorescence is ascribed to the manipulation of the spontaneous emission of the allyl-FL by the photonic stopband, which is verified by the fluorescence spectra of the allyl-FL infiltrated in the CCs with different photonic stopbands. This study will be prospective in bio-imaging and miniature lasers.

We demonstrate low threshold lasing oscillation in a photonic crystal (PhC) laser by using tert-butyl Rhodamine B (t-Bu-RhB) doped gain media. Lactonic t-Bu-RhB is synthesized to improve doping concentration in polymethylmethacrylate (PMMA) films, and then isomerized to the zwitterion form to achieve highly fluorescent gain medium. The t-Bu-RhB doped PMMA film is sandwiched by a pair of polystyrene colloidal crystals to construct a PhC resonating cavity. Single-mode laser oscillation at 592 nm is observed when the PhC resonating cavity is pumped by a Nd:YAG laser. The lasing threshold is 0.12 MW cm−2 utilizing 6.9 wt% t-Bu-RhB doped PMMA films, which is only 1/60 of that with 3 wt% t-Bu-RhB doped PMMA films. The concentration-dependent lasing action is attributed to different gain factors of the t-Bu-RhB doped PMMA films. Furthermore, a spatially and spectrally coherent laser beam from the PhC resonating cavity is verified by exploring the far-field image and angular dependence of the lasing emission. The approach provides a facile and efficient strategy to reduce the lasing threshold for fabricating low threshold PhC lasers.

PMMA-SH/CdSe–Au nanocomposite thin films have been constructed by a layer-by-layer (LBL) assembly method. The LBL assembly process is carried out in a nonpolar solvent by the combination of photopolymerization and adsorption of CdSe–Au nanoparticles. Absorption spectra suggest that the LBL assembly is performed in a stepwise and uniform way. The optical, morphological, thermal, and optical limiting properties of the resultant PMMA-SH/CdSe–Au nanocomposite thin films are characterized by transmission, TEM, TGA and laser measurements. The LBL assembled PMMA-SH/CdSe–Au nanocomposite thin films exhibit good thermal stability, transparency, and optical limiting response to a 532 nm pulsed laser. The optical limiting threshold of the PMMA-SH/CdSe–Au nanocomposite thin film is 13 J cm−2. This study provides a robust and efficient strategy for fabricating transparent polymeric thin films with laser optical limiting property.

3D printing technology has attracted much attention due to its high potential in scientific and industrial applications. As an outstanding 3D printing technology, two-photon polymerization (TPP) microfabrication has been applied in the fields of micro/nanophotonics, micro-electromechanical systems, microfluidics, biomedical implants and microdevices. In particular, TPP microfabrication is very useful in tissue engineering and drug delivery due to its powerful fabrication capability for precise microstructures with high spatial resolution on both the microscopic and the nanometric scale. The design and fabrication of 3D hydrogels widely used in tissue engineering and drug delivery has been an important research area of TPP microfabrication. The resolution is a key parameter for 3D hydrogels to simulate the native 3D environment in which the cells reside and the drug is controlled to release with optimal temporal and spatial distribution in vitro and in vivo. The resolution of 3D hydrogels largely depends on the efficiency of TPP initiators. In this paper, we will review the widely used photoresists, the development of TPP photoinitiators, the strategies for improving the resolution and the microfabrication of 3D hydrogels.

Hydrogels with precise 3D configuration (3D hydrogels) are crucial for biomedical applications such as tissue engineering and drug delivery, which require the improvement of the spatial resolution on both the microscopic and the nanometric scale. In this study, a water soluble two-photon polymerization (TPP) initiator (WI) with high initiating efficiency was prepared by using a poloxamer (PF127) to encapsulate 2,7-bis(2-(4-pentaneoxy-phenyl)-vinyl)anthraquinone via a hydrophilic–hydrophobic assembly. The threshold energy for WI was 6.29 mW at a linear scanning speed of 10 μm s−1, which was much lower than those reported previously. A lateral spatial resolution of 92 nm was achieved as the resolution breakthrough of 3D hydrogels. Finally, the microstructure with high accuracy simulating the morphology of adenovirus was fabricated at the laser power close to the threshold energy of TPP, further demonstrating the ultrahigh resolution of 3D hydrogels.

Two novel carbazole derivatives, BMEPC and BMEMC, were designed, synthesized and first reported as two-photon photosensitizers for DNA photodamage, which showed efficient DNA photocleavage ability under near-infrared light exposure via a two-photon process in anaerobic condition.

We have numerically demonstrated chiral metamaterials based on double-layered asymmetric U-shape split ring resonators. Dual-band circular dichroism is found in the whole frequency regime from 50 to 250 THz by studying the transmission properties. Huge optical activity and the induced negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared regime.A new dual band chiral metamaterial based on asymmetric split ring resonators is proposed, which offer flexible applications in the infrared frequencies.

Here, we have introduced a novel biscarbazolylmethane-based cyanine as a two-photon excited fluorescent probe, 6,6′-bis[2-(1-methylpyridinium)vinyl]-bis(9-methyl-carbazol-3-yl)methane diiodide, which has two vinylpyridinium carbazole moieties connected by a non-rigid methylene bridge. This molecule possesses a larger Stokes shift and enhanced two-photon absorption cross-section than the previously reported vinylpyridinium carbazole monocyanine, which is mainly attributed to the “through-space” type intramolecular charge transfer. The low fluorescence quantum yield and 30-fold fluorescence enhancement once binding with calf thymus DNA highlight this molecule as a promising fluorescence light-up probe for DNA. The obvious induced circular dichroism signals have proved that the molecule with soft-connected bis-cationic centers can specifically interact with various DNA structures. Cell viability study shows that the probe has very low cytotoxicity. The probe exhibits high staining selectivity for mitochondria in living HeLa cells. Its capability to stain nuclear DNA has been confirmed by fixed cell staining. Furthermore, the application for two-photon excited fluorescence imaging demonstrates high potential of the probe for nonlinear bioimaging with 3D resolution.

Hydrogels with a precise 3D configuration (3D hydrogels) are required for a number of biomedical applications such as tissue engineering and drug delivery. Two-photon polymerization (TPP) is an advanced method to fabricate 3D hydrogels. However, TPP of 3D hydrogels has been challenged by the lack of TPP initiators with high efficiency in aqueous medium. In this study, a water soluble TPP initiator (WI) with high fabrication efficiency was prepared by combining hydrophobic 2,7-bis(2-(4-pentaneoxy-phenyl)-vinyl)anthraquinone (N) with a C2v symmetrical structure and 2-hydroxypropyl-β-cyclodextrins through host–guest chemical interaction. Both one and two-photon optical properties of WI have been investigated. In aqueous medium, WI showed a two-photon absorption cross-section of around 200 GM at the wavelength of 780 nm which was much higher compared with those of commercial initiators. The threshold energy of TPP for the resin with WI as a photoinitiator (the molar ratio of N in resin is 0.03%) was 8.6 mW. 3D hydrogels with a woodpile microstructure were further fabricated by using an average power of 9.7 mW and a scanning speed of 30 μm s−1.

An inverse opal hydrogel (IOH) sensor was constructed through colloidal templating photopolymerization of acrylic acid and pemaerythritol-triacrylate. Its dual responsive behaviours to pH and mercury ions (Hg2+) were demonstrated by detecting the shift of the diffraction wavelength. The diffraction wavelength of the IOH sensor was dramatically red-shifted when the pH was increased from 11 to 13, due to the swelling of the hydrogel. The shift of the diffraction wavelength can be directly observed by the naked eye through the colour change of the IOH. A fast response behaviour of the IOH sensor to pH was approximately completed within 3 s. Furthermore, carboxyl groups were used to detect Hg2+ as recognition groups. A low detection limit of 10 nM for Hg2+ was achieved in the optimized IOH sensor. The present work indicates the prospect of constructing multi-responsive IOH sensors using a single recognition group through the facile colloidal templating route.

A high efficiency solar cell based on ZnO nanowire (NW) arrays of different morphology and crystalline quality has been assembled and investigated. According to the basic source of the hydrothermal growing solution, ZnO NW was prepared by using (a) ammonia solution (N method), (b) hexamethylene tetramine (H method) and (c) alternating of N and H (NH method), respectively. The morphology and crystalline quality of the ZnO NW array have been characterized by using scanning electron microscopy, Raman spectroscopy and transmission electron microscopy. The CdS and CdSe nanoparticles were deposited on ZnO NW array, which is applied as a ZnO/CdS/CdSe core/interlay/shell in solar cell with a polysulfide electrolyte and a CoS counter electrode. The results indicate that the photovoltaic behaviour strongly depends on the morphology and crystalline quality of the ZnO NW array. We observe an increasing short-circuit current density of N < NH < H by using ZnO NWs prepared with different methods. The best power conversion efficiency of 2.81% and a short-circuit current of 14.6 mA cm−2 were obtained. The results would open up new avenues towards the potential applications in designing high efficiency quantum dot sensitized solar cells.

We demonstrated an efficient and robust approach for the preparation of polymer/quantum dot (QD) nanocomposite thin films in nonpolar media. By employing photopolymerization based on the thiol-ene reaction, thiol-containing polymer with affinity groups for CdSe@CdS QDs was produced for the buildup of the polymer/CdSe@CdS QD nanocomposite thin films utilizing layer-by-layer assembly. The polymer/QD nanocomposite films were characterized by SEM, TEM, fluorescence spectrometry, thermogravimetric analysis, confocal laser scanning microscopy and time-resolved fluorescence spectrometry. The resulting free-standing polymer/QD nanocomposite films exhibit high fluorescent intensity, moderate transparency, good photostability and thermal stability. We further applied photolithographic patterning in conjunction with an LBL assembly method to fabricate a polymer/CdSe@CdS QD nanocomposite pattern on a flexible substrate. This versatile and facile method provides prospects for the design of novel photonic devices based on the polymer/QD nanocomposite thin films.

We demonstrate the lasing and amplified spontaneous emission in the polymeric inverse opal photonic crystal resonating cavity. The resonating cavity is constructed by sandwiching tert-butyl rhodamine B doped PMMA film with polymeric inverse opal photonic crystals, which work as feedback mirrors. Laser-induced emission experiments reveal lasing or amplified spontaneous emission of the dye molecules in the resonating cavity. Amplified spontaneous emission occurs at the edges of the photonic stop band of the polymeric inverse opal photonic crystal when it partially overlaps with the photoluminescence emission band of the dye molecules. In contrast, lasing action emerges in the resonating cavity when the photonic stop band matches well with the photoluminescence emission band of the dye molecules. Single-mode lasing emission is located at the photonic stop band, indicating the photonic lasing property. The lasing threshold is determined as 4.57 μJ/pulse, and the lasing line width is about 1.0 nm. The present work provides the prospect for constructing low-threshold organic solid-state dye lasers.

Hydrogen bonding compound (E)-2-benzamido-3-(pyridin-2-yl) acrylic acid (1a) was synthesized and characterized by 1H NMR, FT-IR, and X-ray diffraction analysis in comparison to its analog. These analyses show the existence of seven-membered ring intramolecular hydrogen bonding in 1a. The hydrogen bonding results in the increasing of pKa comparing to its analog. Further investigation on the photophysical properties of 1a in selected solvents reveals that strong absorption appears at about 340 nm and dual emission at around 420 and 490 nm. The excited-state intramolecular proton-transfer in 1a is very sensitive to solvent polarity and fluoride ion. Theoretical studies also give evidence of excited-state intramolecular proton-transfer with quite low energy barrier.Highlights► 2-Benzamido-3-(pyridin-2-yl)acrylic acid has 7-membered ring intramolecular H-bond. ► Dual emissions are observed both in solution and solid states. ► Absorption and emission spectra are sensitive to solvents polarity, F− and base. ► Theoretical calculation shows low excited-state intramolecular H transfer barrier.

A series of C2v symmetrical two-photon absorption compounds with anthracene core, 2,7-bis[2-(4-substituted phenyl)-vinyl]-9,10-dipentyloxyanthracenes designated as I, II and III (the substituted groups at the 4-position of phenyl of I, II and III were dimethylamino, methyl and cyano, respectively) were designed and synthesized as initiators in two-photon induced polymerization (TPIP). The anthracene ring was modified by linking vinylphenyl groups to the 2,7-position to extend conjugation system length and two pentyloxy groups to the 9,10-position to serve as electronic donors. Two-photon absorption cross section of I was around 300 GM, which was much larger than the 10 GM of II and 29 GM of III at 800 nm. I of 0.18% molar ratio in resin composed of methacrylic acid and dipentaerythritol hexaacrylate exhibited a dramatically low threshold of 0.64 mW compared with commercial photoinitiator benzil at a scanning speed 10 μm s−1. Moreover, the threshold of photoinitiator I was only increased to 2.53 mW at a scanning speed of 1000 μm s−1. The dependency of threshold on the concentration and exposure time was in accordance with theoretical calculation. Finally, a reasonable mechanism of the two-photon initiating process was proposed. This study provides good prospects for developing low threshold photoinitiator in TPIP.

The synthesis of hybrid nanostructures with controlled size, shape, composition and morphology has attracted increasing attention due to the fundamental and applicable interest. Here, we demonstrate the synthesis and optical properties of hierarchical CdSe–Au hybrid nanostructures with zinc blende (ZB) CdSe nanocrystals (NCs). For 3.5 nm ZB CdSe NCs, one Au cluster was deposited on each CdSe NC. Nevertheless, several Au clusters were selectively deposited on the apexes of 5 nm and 8 nm ZB CdSe NCs, resulting from the different reactivity of crystal facets. Furthermore, hierarchical CdSe–Au nanostructures with complex morphology were organized with the isolated CdSe–Au hybrid NCs by the coalescence of Au domains on the CdSe–Au hybrid NCs. UV-Vis spectra revealed a red tail upon the deposition of Au clusters. The chemical joint of Au on CdSe NCs was further confirmed by fluorescence quenching. The optical limiting performance of CdSe–Au hybrid NCs dispersed in toluene was investigated at 532 nm using a Nd:YAG laser with the pulse width of 8 ns.

Bright fluorescent hollow structural nanoparticles were prepared from 3,6-bis-[2-(4-carboxylic acid)phenylethynyl]-9-pentyl carbazole (I), an amphiphilic molecule with C2v symmetry, by supramolecular interaction including hydrogen bonding, van de Waals interaction and π–π stacking. The nanoparticles with the average diameter of 88 nm exhibited a fluorescence quantum yield of 0.79.

We designed and synthesized a novel two-photon induced photoinitiator with radical quenching moiety, 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-(4-methoxybenzyl)-carbazole (BNMBC), and successfully demonstrated its optical properties, high initiating efficiency in two-photon induced polymerization (TPIP) and capability to fabricate 3D structures with high resolution. The high resolution in TPIP using BNMBC was achieved as compared to the reported photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-benzylcarbazole (BNBC). BNMBC was confirmed to have a large two-photon absorption cross-section of 2367 GM by Z-scan measurement. We investigated the photopolymerization properties of resins R1–R3 in which BNBC, BNBC/phenyl methyl ether (PhOMe) and BNMBC were used as photoinitiators, respectively. The TPIP fabrication experiments exhibited that BNMBC possessed high TPIP initiating efficiency and an effective radical quenching effect. The volumes of polymer fibers fabricated by the TPIP of the photoresist using BNMBC as the photoinitiator were decreased to 20%–30% of those synthesised using BNBC as a photoinitiator. The introduction of a radical quenching group to the photoinitiator resulted in the effective confining effect of radical diffusion compared to the addition of the same molar ratio of radical quencher. This kind of photoinitiator with radical quenching group should benefit the fabrication of precise structures.

We propose an asymmetric three-dimensional (3D) multiphoton polymerization microfabrication method, and successfully demonstrate it through fabricating the size- and shape-controlled stimuli-responsive asymmetric hydrogel microcantilevers. The reversible ion-responsive hydrogel microcantilevers exhibit attractive and controllable bending behavior due to their asymmetric deformation to external ions. The reversible bending direction of microcantilevers completed within only 0.133 s when the surrounding environment was alternated from water to 1 M NaCl solution. Furthermore, the microcantilevers exhibited large total bending angles θT up to 32.9°. The bending behavior can be also strongly influenced by increasing the length of the microcantilevers. The 3D stimuli-responsive hydrogels were demonstrated to be promising for the application of microactuators and micromanipulators. This designable microfabrication technique and the stimuli-responsive behavior of asymmetric microstructure of hydrogel with versatility in the shape would be prospective for developing biomedical microdevices.

The ability of novel branched chromophores that contained a triphenylamine group as donor, naphthalene as π-bridge and pyridyl as acceptor group, to act as two-photon absorption and two-photon induced polymerization initiators were investigated. Linear and nonlinear optical spectra revealed that chromophores with large dipolar moment change gave strong intramolecular charge-transfer characteristics that exhibited enhanced two-photon absorption cross-section. A variety of micro-objects were fabricated, using an acrylate matrix, that contained the novel chromophores as two-photon induced polymerization initiator. Molecular energy levels, electrochemistry and linear absorption spectra, as well as one-photon fluorescence quenching measurements supported the hypothesis that two-photon induced polymerization proceeds via intermolecular charge-transfer from initiator to monomer and, that the chromophore firstly generates the exciton via two-photon absorption and then transfers charge to the acrylate monomer which then polymerises.

We propose and demonstrate a facile room-temperature synthetic method for obtaining water-soluble magnetic Fe3O4 nanoparticles (NPs) by combining the in situ synthesis and decomposition of a magnetic polymer hydrogel. The Fe3O4 NPs with average diameters of 6.3–8.3 nm were synthesized in a cross-linked polyacrylamide (PAAm) hydrogel by coprecipitating iron ions. The decomposition of the magnetic polymer hydrogel by an aqueous solution of sodium hydroxide led to the transfer of Fe3O4 NPs into the aqueous medium. The NPs can be dispersed stably in water for more than three months. The Fe3O4 NPs were characterized by X-ray photoelectron spectra (XPS), X-ray powder diffraction (XRD), transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FT-IR). The saturation magnetization of the Fe3O4 NPs was 44.6 and 54.7 emu g−1 at 300 K and 5 K, respectively. The dried magnetic Fe3O4 NPs were easily dispersed in alkaline aqueous media (pH > ∼8) and kept stable for a long time. This room-temperature synthetic method for water-soluble magnetic Fe3O4 NPs can be expected for wide applications in the preparation of functional water-soluble NPs, such as those used in metals and semiconductors.Graphical abstractHighlights► A facile room-temperature method for achieving water-soluble magnetic Fe3O4 nanoparticles (NPs) by combining in situ synthesis and decomposition of magnetic polymer hydrogel has been demonstrated. ► The Fe3O4 NPs with average diameters of 6.3–8.3 nm were synthesized in a crosslinked polyacrylamide hydrogel. ► The saturation magnetization was 44.6 and 54.7 emu g−1 at 300 K and 5 K, respectively. ► The dried magnetic Fe3O4 NPs were easily dispersed in alkaline aqueous media. ► This study would be prospect for preparing functional water-soluble NPs used in metals and semiconductors.

The nonlinear optical properties of the size-controlled trans-4-[4-(dimethylamino)-N-methylstilbazolium] p-tosylate (DAST) organic nanocrystals (ONCs) have been investigated. The size and monoclinic crystal structure have been demonstrated by the scanning electron microscope, transmission electron microscope, and X-ray diffraction measurement. The DAST ONCs exhibited 6-fold enhanced fluorescence quantum yield and prolonged fluorescence lifetime compared to DAST molecular solution. The evaluations of two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG) microscopes have been implemented for investigating the optical nonlinearities of DAST nanocrystals. The TPEF intensity of DAST ONCs was improved by a factor of 37.3 compared to DAST molecular solution. The extraordinary large two-photon absorption cross section up to 1.72 × 106 GM was observed. DAST ONC was demonstrated as a single crystal from the four-lobe polarization response in the SHG microscope. These results would provide DAST ONCs the opportunity for the potential application in photonics and bioimaging as nonlinear optical materials.

A new family of dendrimers with a naphthaline-core flanked on both sides by triphenylamine-branching was successfully synthesized and presented an increasing two-photon absorption (TPA) cross section from 959 to 9575 GM with the generation number from 1 to 3. These dendrimers can efficiently initiate the acrylate resins to polymerization to obtain very regular diamond structures and display higher two-photon polymerization (TPP) efficiency and sensitivity with the generation number. The overall TPP processes involved in two-photon excitation, intramolecular charge transfer, and intramolecular energy transfer as well as intermolecular electron transfer between initiator and monomer are described. Steady-state fluorescence and time-resolved decay dynamics revealed that the light energy was absorbed by peripheral triphenylamine unit and then transferred to generation 1, the energy funnel. Although strong interaction between dendritic initiator and monomer has been observed based on fluorescence quenching measurements, no intermolecular energy transfer but electron transfer is confirmed by the cyclic voltammograms and HOMO−LUMO measurements. That is, the dendritic initiator first produces the excited state via two-photon absorption, then transfers an electron to an acrylate monomer, and finally induces the later to polymerize.

A new low-bandgap π-conjugated D–A copolymer of squaraine and pyridopyrazine (P1) and a new small molecule squaraine–pyridopyrazine model compound (P2) were synthesized and compared. P1 and P2 exhibit strong NIR absorption and low bandgap (1–1.3 eV). P2 in solution shows an intense and sharp absorption peak at 764 nm, while P1 in solution exhibits a red-shifted and broad absorption peak at 808 nm. The HOMO and LUMO levels of P1 were estimated to be −5.02 and −4.15 eV, while the HOMO and LUMO levels of P2 were estimated to be −5.27 and −3.22 eV, respectively. Polymer P1 exhibits strong two-photon absorption (2PA) at telecommunication wavelengths with 2PA cross sections per repeat unit as high as 2300 GM, 3–5 times that for the small molecule P2. The higher HOMO, the lower LUMO levels, lower bandgap, red-shifted absorption, and stronger two-photon absorption of P1 are attributed to higher degree of conjugation and delocalization of π-electrons in the polymer.

Gold nanoparticles (AuNP’s) prepared through a controllable synthesis and aggregation process are attractive for their unique properties that arise from their surface plasmon resonances (SPRs). However, aggregation-controlled AuNP’s on amorphous surfaces have not been well explored. In this study, we present a simple in situ synthesis method for preparing AuNP’s in which the AuNP’s self-aggregate into microscale Candock-leaf-like structures on a polyelectrolyte film (PEF) surface. In this approach, the PEF plays an important role in adsorbing and storing AuCl4− as well as in controlling the release speed of AuCl4− in the preparation process. The mechanism for forming these Candock-leaf-like structures has been illustrated by both the growth process of gold nanoparticles and the Ostwald ripenning of the aggregations. AuNP’s with a unique structure exhibited significantly enhanced surface Raman scattering and strong superhydrophobicity.

We have prepared and characterized nickel–phosphorus (Ni–P)/polymer composite and demonstrated a method for fabricating three-dimensional (3D) micromachines by combining two-photon polymerization (TPP) of polymer and electroless plating of Ni–P alloy to achieve high mechanical performance and remotely controllable capability. Ni–P electroless plating process has been optimized. The mechanical performance of the Ni–P/polymer composite film, such as the hardness and modulus, was improved to 1.74 and 34.93 GPa with a Ni–P alloy layer, respectively. The Ni–P alloy layer deposited on the surface of the 3D micromachine provides good response capability in the magnetic field. Furthermore, we successfully demonstrate that the as-prepared magnetic 3D micromachine was able to be remotely manipulated expeditiously by the external magnetic field. This study would open up a broad prospect for developing remote manipulated 3D micro/nanomachine with excellent mechanical performance.

A Cu2+-specific colorimetric sensor 1, which is stabilized by an intramolecular hydrogen bonding, was designed and developed. The color of 1 changes from purple to blue on addition of 1.0 μM Cu2+ in aqueous buffer solution, which can be detected by the naked eye. The analytical detection limit for Cu2+ by the naked eye is as low as 1.0 μM. The stoichiometry for 1 and Cu2+ in complex is 2:1 in aqueous solution.

In this article, a carbosilane dendrimer functionalized in the periphery with fluorescein units was prepared, and the optical property of the fluorescent dendrimer as gain medium was investigated. It was found that the dendrimer consisted of a methylphenylsilane core with 16 fluorescein units in its periphery. The dendrimer exhibits high optical-gain enhancement in methanol solution and laser emission was observed, which is located at 527 nm above the lasing threshold of 0.9 mJ/pulse.

In this paper, platinum nanoparticles were prepared in the hydrosilylation reaction, in which carbosilane dendrimer was used as capping agent and stabilizer. UV–vis spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were employed to characterize the reaction system and the obtained Pt nanoparticles. The high SiH/Pt ratios could accelerate the formation of Pt nanoparticles in hydrosilylation reaction. When the hydrosilane was excess in the reaction, the formed Pt nanoparticles were first capped by hydrosilane molecules via Pt–Si bonds and then stabilized by dendrimers. While under the condition of excess olefin, the Pt nanoparticles were directly capped and stabilized by dendrimers via Pt–C bonds. The formed Pt nanoparticles had a good dispersibility with different size.

Two series of azobenzene derivatives were synthesized so as to investigate the effects of intermolecular hydrogen bonding on their photochemistry. Photoisomerization in polymer matrices was investigated under various irradiation conditions using UV pulsed laser light. Rate constants were calculated according to equations for reversible photoisomerization. Although aminoazobenzenes exhibited faster photoisomerization and larger integral rate constants than the corresponding acetylamino derivatives, the latter compounds displayed faster conversion from the trans to the cis form owing to potential intermolecular hydrogen bonding interaction between the acetylamino groups. Long alkyl chain azobenzenes possessed faster photoisomerization rates than those with short alkyl chains.

We propose a novel method for probing aggregation of dendrimers by investigating the isomerization equilibrium between pink zwitterionic form (Z-form) and colorless lactonic form (L-form) of rhodamine B (RhB) molecules in dilute solution. Investigation using carbosiloxane dendrimers (CSiO-D) with different generations as the model dendrimer molecules showed that the equilibrium constant of isomerization of RhB increased dramatically at the critical aggregation concentration (CAC) of dendrimers. The redox potential differences between isomers of RhB indicated that aggregation of CSiO-D accelerated the isomerization of RhB and stabilized the L-form of RhB. The data on Gibbs energy and electrolytic conductivity provided further evidence for confirming the CAC of dendrimers in dilute solution and showed good agreement with our other experimental results. The proposed method is effective in estimating the CAC of dendrimers in dilute solution.

Novel A–π–D–π–A V-shaped 3,6-bis(phenylethynyl)carbazole based chromophores were designed and synthesized as two-photon polymerization (TPP) initiators combining a large two-photon absorption cross-section with facilitated radical formation. 9-Benzyl-3,6-bis(4-nitrophenylethynyl)carbazole (4d) shows a strong two-photon absorption around 800 nm and exhibits very high two-photon polymerization initiating sensitivity with a threshold power of 0.8 mW at the concentration of 0.18 mol%, which is much lower than the threshold power of 6.37 mW found for benzil. The corresponding threshold of laser exposure intensity for TPP is 3.0 × 107 mJ cm−2. The lowest loading of 4d is up to 0.012 mol% with a threshold power of 3.2 mW.

Carbosilane dendrimers with terminal allyl groups were synthesized and used to encapsulate the allyl derivative of fluorescein (allyl-FL) doped in PMMA. The optical property of this system was investigated and the results showed that the concentration of allyl-FL in PMMA could be increased to 4.5 wt% without decrease of the luminescence efficiency by adding the dendrimer into the system. The allyl-FL/dendrimer/PMMA film was embedded into a resonance cavity composed of two pieces of photonic band gap (PBG) materials to form a new-type solid-state laser. A laser emission at 589 nm was obtained when excited with a third harmonic generation (THG) of a pulsed Nd:YAG laser (355 nm) and its full-width at half-maximum of the spectrum was 1.7 nm.

C2v symmetrical anthraquinone derivatives, 2,7-bis(2-(4-dimethylamino-phenyl)-vinyl)anthraquinone (1) and 2,7-bis(2-(4-methoxy-phenyl)-vinyl)anthraquinone (2) were synthesized by Wittig reaction. Their one-photon absorption and fluorescence, as well as two-photon absorption properties were investigated. These compounds showed strong intramolecular charge transfer bands as well as low fluorescence quantum yield. 1 showed a larger two-photon absorption cross-section of 1635 GM than that of 995 GM for 2 at the wavelength of 800 nm. Furthermore, the initiating properties of 1 and 2 were studied by two-photon induced polymerization. The resin with 1 as photoinitiator (R1) possessed higher sensitivity with a threshold energy 3.67 mW at the concentration of 0.02 wt% compared to that of 8.03 mW for 2. The resolution of polymer line, fabricated with R1 at the threshold with the linear scan speed of 50 μm/s, is 105 nm. This investigation on the relationship of resolution and sensitivity indicated higher sensitivity benefit to the improvement of microfabrication resolution.

We designed and synthesized a novel two-photon induced photoinitiator with radical quenching moiety, 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-(4-methoxybenzyl)-carbazole (BNMBC), and successfully demonstrated its optical properties, high initiating efficiency in two-photon induced polymerization (TPIP) and capability to fabricate 3D structures with high resolution. The high resolution in TPIP using BNMBC was achieved as compared to the reported photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-benzylcarbazole (BNBC). BNMBC was confirmed to have a large two-photon absorption cross-section of 2367 GM by Z-scan measurement. We investigated the photopolymerization properties of resins R1–R3 in which BNBC, BNBC/phenyl methyl ether (PhOMe) and BNMBC were used as photoinitiators, respectively. The TPIP fabrication experiments exhibited that BNMBC possessed high TPIP initiating efficiency and an effective radical quenching effect. The volumes of polymer fibers fabricated by the TPIP of the photoresist using BNMBC as the photoinitiator were decreased to 20%–30% of those synthesised using BNBC as a photoinitiator. The introduction of a radical quenching group to the photoinitiator resulted in the effective confining effect of radical diffusion compared to the addition of the same molar ratio of radical quencher. This kind of photoinitiator with radical quenching group should benefit the fabrication of precise structures.

Novel A–π–D–π–A V-shaped 3,6-bis(phenylethynyl)carbazole based chromophores were designed and synthesized as two-photon polymerization (TPP) initiators combining a large two-photon absorption cross-section with facilitated radical formation. 9-Benzyl-3,6-bis(4-nitrophenylethynyl)carbazole (4d) shows a strong two-photon absorption around 800 nm and exhibits very high two-photon polymerization initiating sensitivity with a threshold power of 0.8 mW at the concentration of 0.18 mol%, which is much lower than the threshold power of 6.37 mW found for benzil. The corresponding threshold of laser exposure intensity for TPP is 3.0 × 107 mJ cm−2. The lowest loading of 4d is up to 0.012 mol% with a threshold power of 3.2 mW.

3D printing technology has attracted much attention due to its high potential in scientific and industrial applications. As an outstanding 3D printing technology, two-photon polymerization (TPP) microfabrication has been applied in the fields of micro/nanophotonics, micro-electromechanical systems, microfluidics, biomedical implants and microdevices. In particular, TPP microfabrication is very useful in tissue engineering and drug delivery due to its powerful fabrication capability for precise microstructures with high spatial resolution on both the microscopic and the nanometric scale. The design and fabrication of 3D hydrogels widely used in tissue engineering and drug delivery has been an important research area of TPP microfabrication. The resolution is a key parameter for 3D hydrogels to simulate the native 3D environment in which the cells reside and the drug is controlled to release with optimal temporal and spatial distribution in vitro and in vivo. The resolution of 3D hydrogels largely depends on the efficiency of TPP initiators. In this paper, we will review the widely used photoresists, the development of TPP photoinitiators, the strategies for improving the resolution and the microfabrication of 3D hydrogels.

Hydrogels with a precise 3D configuration (3D hydrogels) are required for a number of biomedical applications such as tissue engineering and drug delivery. Two-photon polymerization (TPP) is an advanced method to fabricate 3D hydrogels. However, TPP of 3D hydrogels has been challenged by the lack of TPP initiators with high efficiency in aqueous medium. In this study, a water soluble TPP initiator (WI) with high fabrication efficiency was prepared by combining hydrophobic 2,7-bis(2-(4-pentaneoxy-phenyl)-vinyl)anthraquinone (N) with a C2v symmetrical structure and 2-hydroxypropyl-β-cyclodextrins through host–guest chemical interaction. Both one and two-photon optical properties of WI have been investigated. In aqueous medium, WI showed a two-photon absorption cross-section of around 200 GM at the wavelength of 780 nm which was much higher compared with those of commercial initiators. The threshold energy of TPP for the resin with WI as a photoinitiator (the molar ratio of N in resin is 0.03%) was 8.6 mW. 3D hydrogels with a woodpile microstructure were further fabricated by using an average power of 9.7 mW and a scanning speed of 30 μm s−1.

We demonstrate low threshold lasing oscillation in a photonic crystal (PhC) laser by using tert-butyl Rhodamine B (t-Bu-RhB) doped gain media. Lactonic t-Bu-RhB is synthesized to improve doping concentration in polymethylmethacrylate (PMMA) films, and then isomerized to the zwitterion form to achieve highly fluorescent gain medium. The t-Bu-RhB doped PMMA film is sandwiched by a pair of polystyrene colloidal crystals to construct a PhC resonating cavity. Single-mode laser oscillation at 592 nm is observed when the PhC resonating cavity is pumped by a Nd:YAG laser. The lasing threshold is 0.12 MW cm−2 utilizing 6.9 wt% t-Bu-RhB doped PMMA films, which is only 1/60 of that with 3 wt% t-Bu-RhB doped PMMA films. The concentration-dependent lasing action is attributed to different gain factors of the t-Bu-RhB doped PMMA films. Furthermore, a spatially and spectrally coherent laser beam from the PhC resonating cavity is verified by exploring the far-field image and angular dependence of the lasing emission. The approach provides a facile and efficient strategy to reduce the lasing threshold for fabricating low threshold PhC lasers.

Here, we have introduced a novel biscarbazolylmethane-based cyanine as a two-photon excited fluorescent probe, 6,6′-bis[2-(1-methylpyridinium)vinyl]-bis(9-methyl-carbazol-3-yl)methane diiodide, which has two vinylpyridinium carbazole moieties connected by a non-rigid methylene bridge. This molecule possesses a larger Stokes shift and enhanced two-photon absorption cross-section than the previously reported vinylpyridinium carbazole monocyanine, which is mainly attributed to the “through-space” type intramolecular charge transfer. The low fluorescence quantum yield and 30-fold fluorescence enhancement once binding with calf thymus DNA highlight this molecule as a promising fluorescence light-up probe for DNA. The obvious induced circular dichroism signals have proved that the molecule with soft-connected bis-cationic centers can specifically interact with various DNA structures. Cell viability study shows that the probe has very low cytotoxicity. The probe exhibits high staining selectivity for mitochondria in living HeLa cells. Its capability to stain nuclear DNA has been confirmed by fixed cell staining. Furthermore, the application for two-photon excited fluorescence imaging demonstrates high potential of the probe for nonlinear bioimaging with 3D resolution.

Hydrogels with precise 3D configuration (3D hydrogels) are crucial for biomedical applications such as tissue engineering and drug delivery, which require the improvement of the spatial resolution on both the microscopic and the nanometric scale. In this study, a water soluble two-photon polymerization (TPP) initiator (WI) with high initiating efficiency was prepared by using a poloxamer (PF127) to encapsulate 2,7-bis(2-(4-pentaneoxy-phenyl)-vinyl)anthraquinone via a hydrophilic–hydrophobic assembly. The threshold energy for WI was 6.29 mW at a linear scanning speed of 10 μm s−1, which was much lower than those reported previously. A lateral spatial resolution of 92 nm was achieved as the resolution breakthrough of 3D hydrogels. Finally, the microstructure with high accuracy simulating the morphology of adenovirus was fabricated at the laser power close to the threshold energy of TPP, further demonstrating the ultrahigh resolution of 3D hydrogels.

A series of C2v symmetrical two-photon absorption compounds with anthracene core, 2,7-bis[2-(4-substituted phenyl)-vinyl]-9,10-dipentyloxyanthracenes designated as I, II and III (the substituted groups at the 4-position of phenyl of I, II and III were dimethylamino, methyl and cyano, respectively) were designed and synthesized as initiators in two-photon induced polymerization (TPIP). The anthracene ring was modified by linking vinylphenyl groups to the 2,7-position to extend conjugation system length and two pentyloxy groups to the 9,10-position to serve as electronic donors. Two-photon absorption cross section of I was around 300 GM, which was much larger than the 10 GM of II and 29 GM of III at 800 nm. I of 0.18% molar ratio in resin composed of methacrylic acid and dipentaerythritol hexaacrylate exhibited a dramatically low threshold of 0.64 mW compared with commercial photoinitiator benzil at a scanning speed 10 μm s−1. Moreover, the threshold of photoinitiator I was only increased to 2.53 mW at a scanning speed of 1000 μm s−1. The dependency of threshold on the concentration and exposure time was in accordance with theoretical calculation. Finally, a reasonable mechanism of the two-photon initiating process was proposed. This study provides good prospects for developing low threshold photoinitiator in TPIP.

The synthesis of hybrid nanostructures with controlled size, shape, composition and morphology has attracted increasing attention due to the fundamental and applicable interest. Here, we demonstrate the synthesis and optical properties of hierarchical CdSe–Au hybrid nanostructures with zinc blende (ZB) CdSe nanocrystals (NCs). For 3.5 nm ZB CdSe NCs, one Au cluster was deposited on each CdSe NC. Nevertheless, several Au clusters were selectively deposited on the apexes of 5 nm and 8 nm ZB CdSe NCs, resulting from the different reactivity of crystal facets. Furthermore, hierarchical CdSe–Au nanostructures with complex morphology were organized with the isolated CdSe–Au hybrid NCs by the coalescence of Au domains on the CdSe–Au hybrid NCs. UV-Vis spectra revealed a red tail upon the deposition of Au clusters. The chemical joint of Au on CdSe NCs was further confirmed by fluorescence quenching. The optical limiting performance of CdSe–Au hybrid NCs dispersed in toluene was investigated at 532 nm using a Nd:YAG laser with the pulse width of 8 ns.