Lewis Acid-Relayed Singlet Oxygen Reaction with Enamines: Selective Dimerization of Enamines to Pyrrolin-4-ones.

Singlet oxygen (1O2)-mediated oxidation represents an attractive strategy for incorporation of oxygen atoms from air under mild and environmentally benign conditions. However, the 1O2 reaction with enamine suffers from fragmentation, leading to very unsuccessful transformation. Here, Lewis acid is introduced to intercept [2 + 2] or "ene" reaction intermediates of the 1O2 reaction and enables oxidative dimerization of enamines to produce pyrrolin-4-ones in good to excellent yields. Mechanistic studies reveal the formation of the imino ketone intermediate from the interaction of 1O2 and enamine, which is able to interact with Lewis acid, relaying the 1O2 reaction in enamine chemistry. For the first time, selective cross-dimerization of two different enamines is achieved. Due to the advantages of mild conditions, high chemoselectivity, and up to 99% yield, a promising strategy has been developed for synthesizing aza-heterocycles under ambient conditions, which can be further applied for the synthesis of imidazolone, quinoxaline, and highly functionalized imine.

Surface-enhanced Raman scattering by the composite structure of Ag NP-multilayer Au films separated by Al2O3.

In the present study, a nanoparticle-multilayer metal film substrate was presented with silver nanoparticles (Ag NPs) assembled on a multilayer gold (Au) film by employing alumina (Al2O3) as a spacer. The SERS performance of the proposed structures was determined. It was suggested that the SERS effect was improved with the increase in the number of layers, which was saturated at four layers. The SERS performance of the structures resulted from the mutual coupling of multiple plasmon modes [localized surface plasmons (LSPs), surface plasmon polaritons (SPPs), as well as bulk plasmon polaritons (BPPs)] generated by the Ag NP-multilayer Au film structure. Furthermore, the electric field distribution of the hybrid system was studied with COMSOL Multiphysics software, which changed in almost consistency with the experimentally achieved results. For this substrate, the limit of detection (LOD) was down to 10-13 M for the rhodamine 6G (R6G), and the proposed SERS substrate was exhibited prominently quantitatively detected capability and high reproducibility. Moreover, a highly sensitive detection was conducted on toluidine blue (TB) molecules. As revealed from the present study, the Ag NP-multilayer Au film structure can act as a dependable SERS substrate for its sensitive molecular sensing applications in the medical field.

An Au Nanofilm-Graphene/D-Type Fiber Surface Plasmon Resonance Sensor for Highly Sensitive Specificity Bioanalysis.

A highly sensitive Au-graphene structure D-type fiber surface plasmon resonance biosensor is presented in this study to specifically detect biomolecules. The method of growing graphene is employed directly on the copper, and then a gold film of optimum thickness is sputtered, and the copper foil is etched to obtain the structure. This method makes the contact closer between the gold layer and the graphene layer to improve surface plasmon resonance performance. The performance of this type of surface plasmon resonance (SPR) sensor has been previously verified both theoretically and experimentally. With the proposed Au-graphene structure D-type fiber biosensor, the SPR behaviors are obtained and discussed. In the detection of ethanol solution, a red shift of 40 nm is found between the refractive index of 1.3330 and 1.3657. By calculation, the sensitivity of the sensor we designed is 1223 nm/RIU. Besides, the proposed sensor can detect the nucleotide bonding between the double-stranded DNA helix structures. Thus, our sensors can distinguish between mismatched DNA sequences.

Visible Light Irradiation of Acyl Oxime Esters and Styrenes Efficiently Constructs ß-Carbonyl Imides by a Scission and Four-Component Reassembly Process.

Acyl radical triggered difunctionalizations of aryl olefins have been realized using oxime ester as the acyl precursor for the first time. Irradiation of fac-Ir(ppy)3 and oxime ester by visible light caused scission into three components, which recombined with olefins to yield significant ß-carbonyl imides showing good functional group tolerance and high atom economy. Control experiments as well as spectroscopic and electrochemical studies revealed the efficient intermolecular reorganization of oxime ester into styrene with the aid of solvent exchange.

Direct Arylation of Unactivated Alkanes with Heteroarenes by Visible-Light Catalysis.

The functionalization of aliphatic C-H bonds is both a major challenge and a desirable goal in organic synthesis. Here, we describe the successful arylation of unactivated alkanes with heteroarenes by using iridium polypyridyl complexes as the photocatalyst and persulfate as the HAT catalyst precursor under visible-light irradiation. This reaction features good functional group tolerance and broad scope with regard to both alkane and heteroarene substrates (37 examples), which allows direct access to alkyl-substituted N-heteroarenes, a key structural motif in natural products and bioactive molecules.

Photocatalytic C-C Bond Activation of Oxime Ester for Acyl Radical Generation and Application.

A unified strategy to generate acyl radical from oxime ester via selective C-C bond activation is reported. Under visible-light irradiation, single-electron transfer from fac-Ir(ppy)3 to related oxime takes place followed by a fast ß-fragment of C-C bond to yield aryl and aliphatic acyl radicals, subsequently captured by diverse Michael acceptors. More interestingly, the single-electron transfer enables coupling with energy transfer of the excited fac-Ir(ppy)3 via enone intermediate formed in situ for cyclobutane formation.

1886-nm mode-locked and wavelength tunable Tm-doped CaF2 lasers.

A 3 at.% Tm-doped CaF2 crystal was grown successfully and used as a gain medium. A high-efficiency continuous-wave laser and wide tuning performance were demonstrated in this crystal, and passive mode-locking laser operation was realized for the first time, to the best of our knowledge. For continuous-wave operation, the maximum output power was 2.71 W with a high slope efficiency of 70.3%. Using a quartz birefringent filter, a continuous tuning range of approximately 190 nm was observed in the tuning mode. In addition, a passively mode-locked Tm3+:CaF2 laser emitting at 1886.8 nm was achieved with a semiconductor saturable absorber mirror. At an absorbed pump power of 2.65 W, a pulse duration with tens of picoseconds was obtained at a pulse repetition rate of 96.35 MHz.

Efficient continuous-wave and passive Q-switched mode-locked Er3+ : CaF2-SrF2 lasers in the mid-infrared region.

An Er3+-doped CaF2-SrF2 mixed crystal was grown using the temperature gradient technique, and its laser characteristics were studied. In a compact linear cavity, a continuous-wave output power of 712 mW was obtained with the highest slope efficiency of 41.4%. Using a semiconductor saturable absorber mirror, a passive Q-switched mode-locked Er3+:CaF2-SrF2 laser emitting at 2729.5 nm was demonstrated for the first time, to the best of our knowledge. The maximum average output power of 125 mW was obtained at an absorbed pump power of 1.81 W, and the repetition rate of the Q-switched envelope was 4.17 kHz. The mode-locked pulses in the Q-switched pulse envelope had a repetition rate of 136.3 MHz, and its duration was estimated to be approximately 1.78 ns. These results indicate that the Er3+-doped CaF2-SrF2 mixed crystal is promising for the development of an ultrafast laser in the mid-infrared regime.

Mid-infrared self-Q-switched Er, Pr:CaF2 diode-pumped laser.

A diode-end-pumped self-Q-switched mid-infrared laser was demonstrated with Er3+, Pr3+ co-doped CaF2 crystal for, to the best of our knowledge, the first time. Maximum average output power of 262 mW was achieved and the corresponding slope efficiency was 14.9%. Stable self-Q-switched laser pulses as short as 718 ns were obtained with a repetition rate of 52.63 kHz at the center wavelength of 2803.7 nm. This highly compact nanosecond laser using a 3 at. % Er3+ and 0.03 at. % Pr3+ co-doped CaF2 crystal is free from any active or passive modulators in cavity, potentially promising for a micro and integrated diode-pumped mid-infrared laser system.

Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF2 single crystals.

The spectral properties and laser performance of Er:SrF2 single crystals were investigated and compared with Er:CaF2. Er:SrF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er3+:4I11/2 level) than those of Er:CaF2 crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 µm were demonstrated in both 4at.% and 10at.% Er:SrF2 single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF2 with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.

Radical Addition of Hydrazones by α-Bromo Ketones To Prepare 1,3,5-Trisubstituted Pyrazoles via Visible Light Catalysis.

A novel efficient tandem reaction of hydrazones and α-bromo ketones is reported for the preparation of 1,3,5-trisubstituted pyrazoles by visible light catalysis. In this system, the monosubstituted hydrazones show wonderful reaction activity with alkyl radicals, generated from α-bromo ketones. A radical addition followed by intramolecular cyclization affords the important pyrazole skeleton in good to excellent yields. This efficient strategy under mild conditions with wide group tolerance provides a potential approach to the 1,3,5-trisubstituted pyrazoles.

A facile method to immobilize cucurbituril on surfaces through photocrosslinking with azido groups.

We develop a facile method to immobilize cucurbituril on silicon substrates through photochemical reaction with azido groups. Combining photolithography and the competitive molecular recognition between CB[7] and acridine orange base or 1-adamantanecarboxylic acid, a patterned surface with reversible fluorescence emission can be obtained.

Passively mode-locked Yb3+:Sc2SiO5 laser with reflection-type single-walled carbon nanotube absorber.

A reflection-type single-walled carbon nanotube saturable absorber fabricated by a vertical evaporation method was to our knowledge first used in a passively mode-locked Yb(3+):Sc(2)SiO(5)(Yb:SSO) laser. The laser operated at a repetition frequency of 94 MHz with a central wavelength of 1062.6 nm. A short pulse duration of 1.8 ps was produced with an average power of 349 mW; and the highest pulse energy of 3.7 nJ, corresponding to its maximum peak power, can reach 2.1 kW.

Continuous transform of transverse modes and transitional status analysis in solid-state laser.

With the agility of cavity control in solid-state-laser, we report abundant experimental phenomena of relatively complete Laguerre-Gaussian (LG) transverse multimodes transformation process including both stable and transitional status in a diode pumped Nd:YVO4 microcavity laser. Cavity structure, absorber, pump power, etc, synthetically have been found to contribute such abundant generation of patterns.