A Molecular Cage Accessed by Threefold Click Reaction of a C3v-Symmetric Triazido-Functionalized Tribenzotriquinacene.

The hitherto unknown hexakis(halomethyl)-functionalized tribenzotriquinacenes (TBTQs) 9 and 10 were synthesized from the key 4b,8b,12b-tribromo-TBTQ derivative 6 by an improved route in 67% overall yield. Extension of the bowl-shaped framework of 9 or 10 by threefold condensation with propargylamine or 2-azidoethylamine afforded the corresponding TBTQ-trialkyne 11 and TBTQ-triazide 12, respectively. While attempts to construct bis-TBTQ cages, including homodimerization of 11 and heterocoupling of 11 with 12, were unsuccessful, triazide 12 was found to undergo threefold [3 + 2]-cycloaddition with 3-ethynylaniline and phloroglucinol tripropargyl ether under click chemistry conditions. The latter reaction enabled facile capping of the TBTQ bowl to give the novel cage compound 5 in 22% yield.

A Paternò-Büchi Reaction of Aromatics with Quinones under Visible Light Irradiation.

Reported herein is a Paternò-Büchi reaction of aromatic double bonds with quinones under visible light irradiation. The reactions of aromatics with quinones exposed to blue LED irradiation yielded oxetanes at -78 °C, which was attributed to both the activation of double bonds in aromatics and the stabilization of oxetanes by thiadiazole, oxadiazole, or selenadiazole groups. The addition of Cu(OTf)2 to the reaction system at room temperature resulted in the formation of diaryl ethers via the copper-catalyzed ring opening of oxetanes in situ. Notably, the substrate scope was extended to general aromatics.

Broadband and efficient multi-mode fiber-chip edge coupler on a silicon platform assisted with a nano-slot waveguide.

Mode-division multiplexing (MDM) has been extensively utilized to expand the capacity of chip-scale or fiber-based optical communication, whereas it is still challenging to implement the MDM for fiber-chip optical interconnects due to the huge mode mismatch between few-mode fiber (FMF) and multi-mode waveguide. In this work, we propose and design a silicon integrated six-mode edge coupler assisted with a slot waveguide, which achieves the efficient direct conversion of multiple modes between the waveguide and fiber in a broad bandwidth. Based on the principle of mode conversion, this edge coupler enables the mode conversion between six linear polarization (LP) modes (i.e. LPx/y01, LPx/y11a, LPx/y11b) in FMF and six on-chip waveguide modes (i.e. TE0, TE1, TE2, TM0, TM1, TM2) with low insertion loss, low mode crosstalk and broad bandwidth. The obtained results show that over the whole C-band the efficiency of mode conversion is higher than 98% and the mode crosstalk is low than -19 dB, while the total coupling loss is higher than 85%. The favorable results offer an important reference for designing related broadband photonic devices, and the presented scheme could be potentially exploited to further increase the transmission capability for prospective fiber-chip optical interconnections and communications.

Efficient mode coupling between a few-mode fiber and multi-mode photonic chip with low crosstalk.

The mode-division multiplexing technology has been developing slowly in the field of fiber-chip-fiber optical interconnects, mainly limited by the inefficient mode coupling between few-mode fiber and multi-mode photonic chip. Here we propose and design a multi-mode coupler composed of tapered few-mode fiber and silicon integrated multistage waveguide tapers, which allows the direct coupling between high-order fiber modes and high-order waveguide modes with high coupling efficiency and low crosstalk. Based on the edge coupling scheme, the six linear polarization modes (LP01x/y, LP11a x/y, LP11bx/y) in few-mode fiber are firstly coupled into the integrated waveguide with low insertion loss, then the input modes are converted to the desired waveguide modes (TE0, TE1, TE2, TM0, TM1, TM2) with low mode crosstalk relying on the mode evolution principle. The obtained results show that the coupling efficiency is higher than 87%, while for the mode conversion process, the efficiency is higher than 99% and the mode crosstalk is lower than -25 dB. The favorable performance achieved may open new perspectives for diverse mode-division multiplexing applications, enabling efficient capacity scaling in fiber-chip-fiber optical interconnects and optical communication systems.

Fundamental analyses of fabrication-tolerant high-performance silicon mode (de)multiplexer.

Mode-division multiplexing (MDM) has been extensively exploited to expand the capacity of chip-scale optical interconnects, whereas high-volume manufacturing of on-chip mode (de)multiplexers is still full of challenges. In this paper, we analyze the fabrication errors (sidewall, width, height) of silicon mode (de)multiplexer and present two cases of fabrication-tolerant high-performance silicon mode (de)multiplexer. The presented mode (de)multiplexer could eliminate the mode mismatch and mode hybridization caused by the fabrication errors. When sidewall errors are 0°, 5°, width errors are 0, ± 20, ± 30 nm, and height errors are 0, ± 10 nm, the designed fabrication-tolerant high-performance silicon mode (de)multiplexer can achieve low excess loss less than 2.5 dB and low inter-mode crosstalk less than -15 dB over a broad bandwidth from 1500 to 1600 nm. The obtained results provide an important guideline for designing fabrication-tolerant photonic integrated circuits on silicon platform, which could be applied to the prospective high-volume manufacturing and large-scale integration.

LEAF TIP RUMPLED 1 Regulates Leaf Morphology and Salt Tolerance in Rice.

Leaf morphology is one of the important traits related to ideal plant architecture and is an important factor determining rice stress resistance, which directly affects yield. Wax layers form a barrier to protect plants from different environmental stresses. However, the regulatory effect of wax synthesis genes on leaf morphology and salt tolerance is not well-understood. In this study, we identified a rice mutant, leaf tip rumpled 1 (ltr1), in a mutant library of the classic japonica variety Nipponbare. Phenotypic investigation of NPB and ltr1 suggested that ltr1 showed rumpled leaf with uneven distribution of bulliform cells and sclerenchyma cells, and disordered vascular bundles. A decrease in seed-setting rate in ltr1 led to decreased per-plant grain yield. Moreover, ltr1 was sensitive to salt stress, and LTR1 was strongly induced by salt stress. Map-based cloning of LTR1 showed that there was a 2-bp deletion in the eighth exon of LOC_Os02g40784 in ltr1, resulting in a frameshift mutation and early termination of transcription. Subsequently, the candidate gene was confirmed using complementation, overexpression, and knockout analysis of LOC_Os02g40784. Functional analysis of LTR1 showed that it was a wax synthesis gene and constitutively expressed in entire tissues with higher relative expression level in leaves and panicles. Moreover, overexpression of LTR1 enhanced yield in rice and LTR1 positively regulates salt stress by affecting water and ion homeostasis. These results lay a theoretical foundation for exploring the molecular mechanism of leaf morphogenesis and stress response, providing a new potential strategy for stress-tolerance breeding.

Organochlorine Pesticide Ban Facilitated Reproductive Recovery of Chinese Striped Hamsters.

Organochlorine pesticides (OCPs) have been used worldwide on an enormous scale over the last century but are banned globally due to environmental persistence and ecotoxicity in recent decades. The long-term effects of OCP ban for agricultural use in China since 1983 on the reproductive health of small terrestrial mammals have never been evaluated in the field. We examined the residue dynamics of OCPs and the reproductive performance of Chinese striped hamsters (Cricetulus barabensis) in North China Plain during 1983-2010 and concluded that the exposure levels of OCPs in hamsters drastically decreased from 2900 ± 740 to 25.2 ± 6.88 ng/g with an average half-life of 5.08 yrs, coinciding with the observed reproductive recovery of hamsters. The population-based reproductive performance of hamsters was significantly and negatively associated with OCP exposure levels after adjusting the contributions from climate and population density factors, indicating that the ban of OCPs has facilitated the reproductive recovery of hamsters by up to 81% contribution. Our findings suggest that the OCP ban is effective to restore reproduction of small terrestrial mammals. Integration of population biology and environmental science is essential to assess the impacts of persistent organic pollutants on ecological safety and biodiversity loss under accelerated global change.

Multimode Fano resonances for low-power mode switching.

Intensive research in photonics has discovered many original and fascinating optical phenomena associated with the physics of Fano resonances. Here we extend the research of Fano resonance to on-chip multiple modes and high-order mode, which can be called multimode Fano resonance. By exploiting both wavelength and mode degrees of freedom, we demonstrate a compact structure to engineer wavelength- and shape-controlled multimode Fano resonances on an integrated photonic platform. Both simulated and experimental results indicate that the unambiguous asymmetric spectra line shapes for both transverse electric modes (${{\rm TE}_0}$TE0 and ${{\rm TE}_1}$TE1) can be further applied to low-power mode switching. The demonstrated on-chip multimode Fano resonances scheme may provide a new perspective for exploring the advantages and applications of multimode Fano resonances in integrated photonics.

Chiral Derivatives of 2-Aminotribenzotriquinacene: Synthesis and Optical Resolution.

Starting from a hitherto unknown 2-aminotribenzotriquinacene, several 2-amino-3-X-substituted TBTQ derivatives, all bearing a single ortho-difunctionalized indane wing, were synthesized as rigid and chiral building blocks for the potential construction of complex supramolecular architectures. Efficient access to two pairs of enantiomeric TBTQ derivatives, namely, the peripheral ortho-nitroaniline (X = NO2) and the related anthranilic acid (X = CO2H), was developed using chiral auxiliaries as the resolving reagents. The structure of the intermediate diastereomers was confirmed by 1H and 13C NMR spectroscopy, high-resolution mass spectroscopy (HRMS), and polarimetry. The absolute configuration of the optically active derivatives was confirmed by quantum chemical time-dependent density functional theory (TD-DFT) calculations of the theoretical electronic circular dichroism (ECD) spectra and by single-crystal X-ray structure analysis of a synthesis intermediate.

Feedback-enabled adaptive underwater twisted light transmission link utilizing the reflection at the air-water interface.

Line-of-sight link is widely used in common free-space optical (FSO) laser communications between two fixed locations. While in practical underwater wireless optical communications (UWOC), the environment is relatively complicated. In some scenarios there exist irremovable obstacles, which block the line-of-sight optical link. Fortunately, the air-water interface can function as a natural mirror to enable non-line-of-sight optical link using the total internal reflection. Very recently, twisted light beams carrying orbital angular momentum (OAM) have attracted researchers' great attention to improve the transmission capacity in UWOC. Here, we propose and experimentally demonstrate a non-line-of-sight underwater twisted light transmission link utilizing the total internal reflection at the air-water interface. To overcome the beam fluctuation and drift caused by the change of interface states, we develop a proof-of-concept adaptive feedback system to provide a stable output. Moreover, we study the degrading effects of the slight wind effect, the salinity (turbidity) effect, and the vertical thermal gradient-induced turbulence effect. The results show that the water wave caused by the slight wind causes the most beam drift, the thermal gradient causes the most distortions, and the salinity causes the most power loss.

Generating and synthesizing ultrabroadband twisted light using a compact silicon chip.

Compact and broadband manipulation of spatial modes is important in applications exploiting the space domain of light waves. Here, we demonstrate chip-scale generation and synthesization of ultrabroadband orbital angular momentum (OAM) modes (twisted light) on a silicon platform. By introducing a subwavelength holographic fork grating on top of a silicon waveguide, the in-plane guided mode is converted to the free-space OAM mode. Inputs from both sides of the waveguide enable the synthesization of OAM modes. We also characterize wavelength-dependent emission efficiency, offset angle, and purity with favorable performance. The chip-scale ultrabroadband OAM generator and synthesizer may find potential applications in multidimensional optical communications and quantum key distribution.

Biconcave and Convex-Concave Tribenzotriquinacene Dimers.

A new chiral tribenzotriquinacene bearing an ortho-bromoaniline nucleus was synthesized and optically resolved. The individual enantiomers, the absolute configuration of which was confirmed by single-crystal X-ray structure analysis, were stereoselectively converted into the same pyrazine-fused syn-bis-TBTQ derivative by chirality-assisted Buchwald-Hartwig amination. The corresponding diastereomeric anti-dimer was obtained alongside the syn-dimer from the racemic sample under similar reaction conditions. X-ray structure analysis of the dimers confirmed the mutual biconcave and convex-concave configuration of their TBTQ moieties and the preservation of the orthogonal orientation of the indane wings within each of them.

Construction of the tetracyclic core of (±)-cycloclavine and 4-amino Uhle's ketone.

A rapid construction of the tetracyclic core (±)-2 of (±)-cycloclavine (1) was accomplished in seven steps and 24% overall yield from commercially available aldehyde 7. Key features include a domino Friedel-Crafts/nitro-Michael reaction to construct the C ring and an intramolecular ammonolysis of a diester to close the D ring. In addition, a versatile 4-amino Uhle's ketone (±)-3 was afforded rapidly in five steps and 43% overall yield.

Tribenzotriquinacene-Based Crown Ethers: Synthesis and Selective Complexation with Ammonium Salts.

Two tribenzotriquinacene-based crown ethers, TBTQ-dibenzo-24-crown-8 5 and TBTQ-benzo-21-crown-7 6, were prepared from the key TBTQ intermediate, 2,3-dihydroxy-4b,8b,12b,12d-tetramethyltribenzotriquinacene (13), which in turn was synthesized in six steps using two variants of our cyclodehydration method on a multigram scale. The host-guest complexation properties of the TBTQ-based crown ethers 5 and 6 with a paraquat derivative, 16, and two secondary ammonium salts, 17 and 18, were studied by 1H NMR spectroscopy and mass spectrometry. It was found that host 5 binds to the paraquat derivative 16 as a 1:1 complex in CDCl3/CD3CN solution with an association constant of Ka = (9.2 ± 1.8) × 102 M-1, whereas no complexation was found for 17 and 18. In contrast, the TBTQ-crown ether 6 assembles selectively with dibutylammonium hexafluorophosphate 18 as a 1:1 complex in CDCl3/CD3COCD3 [Ka = (5.0 ± 1.4) × 102 M-1], for which a threaded [2]pseudorotaxane structure is assumed.

Total Synthesis of (-)-Chanoclavine I and an Oxygen-Substituted Ergoline Derivative.

An efficient and direct route to ergot alkaloid (-)-chanoclavine I (3) is described using the inexpensive compound (2R)-(+)-phenyloxirane (15) as a chiral pool in 13 steps with 17% overall yield. Key features of the synthesis include a palladium-catalyzed intramolecular aminoalkynylation of terminal olefin and a rhodium-catalyzed intramolecular [3 + 2] annulation. An oxygen-substituted ergoline derivative (-)-25 was also achieved by using the same strategy.

A ratiometric mitochondria-targeting two-photon fluorescent probe for imaging of nitric oxide in vivo.

A two-photon ratiometric fluorescent probe (Mito-N) has been developed for monitoring mitochondrial nitric oxide (NO) in vivo. Mito-N exhibited excellent selectivity and sensitivity toward NO among various ROS/RNS. The successful two-photon imaging of mitochondrial NO proved that Mito-N is a powerful noninvasive imaging tool in living systems.

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible-Light Photoredox Catalysis.

We have developed a highly efficient aryl migration from an aryl ether to a carboxylic acid group through retro-Smiles rearrangement by visible-light photoredox catalysis at ambient temperature. Transition metals and a stoichiometric oxidant and base are avoided in the transformation. Inspired by the high efficiency of this transformation and the fundamental importance of C-O bond cleavage, we developed a novel approach to the C-O cleavage of a biaryl ether to form two phenolic compounds, as demonstrated by a one-pot, two-step gram-scale reaction under mild conditions. The aryl migration exhibits broad scope and can be applied to the synthesis of pharmaceutical compounds, such as guacetisal. Primary mechanistic studies indicate that the catalytic cycle occurs by a reductive quenching pathway.

o-Quinones Derived from Tribenzotriquinacenes: Functionalization of Inner Bay Positions and Use for Single-Wing Extensions.

Through a surprisingly nonregioselective oxidation process, the reaction of two analogous 2-hydroxy-substituted tribenzotriquinacenes (TBTQs) 8a/8b by o-iodoxybenzoic acid was found to afford the corresponding Cs- and C1-symmetrical TBTQ-o-quinones 6a/6b and 7a/7b, respectively, in 1:1 ratio and excellent combined yields. This finding represents the first example of direct introduction of a functional group into a sterically hindered, inner bay-positions of a parent TBTQ skeleton. In contrast, the analogous reaction with 1-hydroxy-TBTQ 15 failed to produce the desired o-quinone 7a. After reduction of the quinones 6a and 7a to the corresponding catechols 17 and 23, electrophilic aromatic substitution could also be realized at the activated inner bay-position(s) to afford several tri- and tetrafunctionalized TBTQ compounds 18, 21, and 25. The Cs-symmetrical o-quinone 6a was converted into further single-wing extended derivatives such as TBTQ-based phenazines 27a-f, through condensation reactions, and to benzodioxine derivative 32 by Diels-Alder reaction with tetracyclone. The novel TBTQ-quinones and the corresponding TBTQ-catechols offer a variety of new accesses to single-wing-extended and -functionalized TBTQ derivatives.

Indolo-quinoline boron difluoride dyes: synthesis and spectroscopic properties.

Novel indolo-quinoline compounds were efficiently prepared via a Povarov-type reaction, and the structures were further modified by a Suzuki coupling reaction. The corresponding BF2-rigidified complexes were prepared and their spectroscopic properties were characterized with large Stokes shifts (up to 211 nm) and up to near-infrared (NIR) wavelength (667 nm). The synthetic complexes could be used as new fluorescent dyes.

Facile Assembly of Chiral Metallosquares by Using Enantiopure Tribenzotriquinacene Corner Motifs.

Invited for the cover of this issue are Wen-Rong Wu, Guang-Jie Xia, and Hak-Fun Chow of The Chinese University of Hong Kong, Xiao-Ping Cao of Lanzhou University and Dietmar Kuck of Bielefeld University. The image depicts how different routes can lead to the same goal. Read the full text of the article at 10.1002/chem.201501556.