Hai-Yan Lu

Turn-On Fluorescent Sensor for Selective Detection of Zn2+, Cd2+, and Hg2+ in Water

A new fluorescent chemosensor based on a helical imide as fluorophore and a cyclen moiety as ionophore was synthesized, which not only showed enhanced fluorescent responses in the presence of Zn(2+), Cd(2+), and Hg(2+) but also could simultaneously and selectively distinguish the three cations in a simulated physiological condition with the help of cysteine as an auxiliary reagent.

Synthesis and Structures of Multifunctionalized Helicenes and Dehydrohelicenes: An Efficient Route to Construct Cyan Fluorescent Molecules

Helicenes, a class of molecules that consist of ortho-fused aromatic rings with helical chirality, have attracted great interest owing to their unique structural features and wide potential applications in chiral materials, biomolecular recognition, and asymmetric synthesis. Since Newman and Lednicer reported the first helicene in 1956, various methods for synthesis of helicenes including successive Diels– Alder reactions, cyclotrimerizations of acetylenes, carbenoid couplings, electrophilic aromatic cyclizations, radical cyclizations, olefin metathesis, cycloisomerization, and Friedel–Crafts-type cyclizations have been described. However, in most cases, complicated precursors, expensive and sensitive metallic catalysts or harsh reaction conditions were needed, and the products were usually prepared on a small scale. In particular, functionalized helicenes were obtained by multistep reactions, and the precursors were generally difficult to access. The direct functionalization of helicenes is undoubtedly the most effective way to prepare the multifunctionalized helicenes, but few of them have been reported to date, which to a certain extent restricts the practical applications of the helicene derivatives. Dehydrohelicenes are compounds in which the two heli ACHTUNGTRENNUNGcal termini of a helicene are connected by a s bond. As a special class of polycyclic aromatic hydrocarbon (PAH), they could have the wide potential applications in materials science. However, few reports on the cyclodehydrogenation of helicenes were known. Recently, Xue and Scott reported a thermal cyclodehydogenation of [5]heli ACHTUNGTRENNUNGcene by flash vacuum pyrolysis at 1000 8C, but under the same conditions, a significant portion of benzo[5]helicene stayed unchanged. Herein, we report 1) a convenient and efficient synthesis of a dimethoxy-substituted benzo[5]helicene and a benzo[7]helicene, 2) direct bromination of the benzo[5]helicene and synthesis of a series of multifunctionalized [5]helicenes by the Suzuki–Miyaura cross-coupling reactions, and 3) the further oxidative cyclodehydrogenation of the [5]helicene derivatives to afford a series of multifunctionalized dehydro[5]helicene (or naphthoperylene) derivatives with the cyan fluorescent properties and high quantum yields. Synthesis of the helicenes is depicted in Scheme 1. Starting from the commercially available 7-methoxy-3,4-dihydronaphthalen-1 ACHTUNGTRENNUNG(2H)-one 1, the diene 2 was obtained in 60 % yield for two steps. The Diels–Alder reaction between diene 2 and the benzyne from 2-carboxybenzenediazonium chloride gave the compound 3, which was then dehydronated by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to afford the benzo[5]helicene 4 in 97 % yield. According to a similar ap-

Tetrahydro[5]helicene-based full-color emission dyes in both solution and solid states: synthesis, structures, photophysical properties and optical waveguide applications

A series of tetrahydro[5]helicene-based dye molecules were efficiently synthesized and the helical structural features of their tetrahydro[5]helicene skeletons were confirmed by the crystal structures. The substituent effect of the dyes on their photophysical properties was then investigated. Consequently, it was found that compared with hydroxymethyl and ester groups, the introduction of imide to the tetrahydro[5]helicene skeleton could result in not only red shifts of their absorption and emission bands, but also higher quantum yields and larger Stokes shift. Especially, intense full-color fluorescence emissions in both solution and solid states could be achieved just by changing the substituents with different electron-donating abilities in the tetrahydro[5]helicene imide skeleton. Moreover, a significant solvent-effect on the emissions of the tetrahydro[5]helicene-based organic dyes was also found. The density functional theory calculations further demonstrated that with the increase of the electron-donating ability of the substituents, the energy gaps of the tetrahydro[5]helicene-based dyes gradually decreased, which theoretically elucidated the substituent effect of the dyes on their photophysical properties. Additionally, an optical waveguide application of the tetrahydro[5]helicene-based imide dye is shown as well.

A new fluorescence-switch based on supermolecular dyad with (tetraphenylporphyrinato)zinc(II) and tetrathiafulvalene units

A supermolecular dyad based on zinc porphyrin has been constructed by axial coordination to a pyridine-appended tetrathiafulvalene (TTF). This dyad has been characterized by optical absorption, fluorescent spectra, computational and electrochemical methods. The estimated binding constant (K), fluorescence quenching effect and the electrochemical behaviors not only revealed the stable complexation but also suggested the existence of the intra-supermolecular interactions between the porphyrin and TTF units. As the fluorescence of this dyad could be modulated by sequential oxidation and reduction of the TTF unit, a new redox fluorescence switch based on this supermolecular dyad has been constructed.

Simple, efficient and selective colorimetric sensors for naked eye detection of Hg2+, Cu2+ and Fe3+

Compounds 3 and 4 are all push–pull molecules containing both a donor 1,3-dithiole ring and an acceptor carbonyl group or thiocarboyl group, and their structures confer them with special spectroscopic properties. Their recognition behaviors towards metal ions were explored by UV-vis spectral analysis, and the results showed that combination of 3 and 4 could efficiently detect Hg2+, Cu2+ and Fe3+. The instant color changes induced by the addition of corresponding metal ions make them excellent naked eye sensors for the detection of heavy metal ions.

Complexation of a Pentiptycene-Based Tweezer-Like Receptor with Paraquat Derivatives: Ion-Controlled Binding and Release of the Guests

A new tweezer-like receptor containing a pentiptycene unit and a benzene ring linked by two crown ether chains has been synthesized. It could form stable complexes with paraquat derivatives with different functional groups in solution and in the solid state. It was found that the complexes dissociated upon two one-electron reduction of the bipyridinium ring. Moreover, binding and release of the guest molecules could also be easily controlled by the addition and removal of potassium ion.

Benzo[5]helicene-based conjugated polymers: synthesis, photophysical properties, and application for the detection of nitroaromatic explosives

A series of conjugated polymers based on benzo[5]helicene have been synthesized by employing Sonogashira cross coupling, Suzuki–Miyaura cross coupling and Yamamoto homocoupling reactions. The photophysical properties of these polymers and their fluorescence responses to the nitroaromatic compounds have then been investigated. Quantitative analysis of the fluorescence titration profiles of the polymers with nitroaromatics in solution exhibited that these electron-rich conjugated polymers could selectively detect the nitroaromatic explosives among the electron-deficient aromatic compounds, and the polymers displayed different responses to the nitroaromatics with similar structures. Moreover, the thin film of polymer P2 also sensed the saturated vapors of nitroaromatics sensitively and selectively at room temperature, and the sensing process of the film was reproducible. The fluorescence intensity of P2 revealed a reduction of 87% upon exposure to DNT vapor, and of 70% to TNT vapor in only 10 s. Thus, these new conjugated polymers can be excellent fluorescence sensory materials for detecting nitroaromatic explosives.

Click and Patterned Functionalization of Graphene by Diels–Alder Reaction

Chemical functionalization is a promising approach to controllably manipulate the characteristics of graphene. Here, we designed cis-dienes, featuring two dihydronaphthalene backbones, to decorate a graphene surface via Diels-Alder (DA) click reaction. The installation of a diene moiety into a nonplanar molecular structure to form cis-conformation enables a rapid (∼5 min) DA reaction between graphene and diene groups. Patterned graphene of sub-micrometer resolution can be obtained by easily soaking poly(methyl methacrylate)-masked graphene in solution of hydroxyl-substituted cis-diene at room temperature. The functionalization degree can be further controlled by carrying out the reaction at higher temperature. The present result gives important insight into the effect of molecular conformation on the graphene functionalization process, and provides an effective and facile method for graphene functionalization.

Dioxygen‐Triggered Transannular Dearomatization of Benzo[5]helicene Diols: Highly Efficient Synthesis of Chiral π‐Extended Diones

Oxidative dearomatization is a powerful strategy in organic synthesis. However, reports on using dioxygen as the oxidant, as it is environmentally friendly, readily available (air), and easy to handle, are rather limited. Helicene diols can undergo transannular dearomatization triggered by dioxygen to give diones in quantitative yields within several minutes. By virtue of this, the chirality is successfully transferred from helicity to central chirality to form distorted π-extended diones having two all-carbon quaternary stereocenters. The optical resolution was achieved by column chromatography, and the structures and the absolute configurations of the chiral diones were determined by X-ray analysis.

A concise synthesis of the (−)-allosamizoline aminocyclopentitol based on pyridinium salt photochemistry

Abstract The (−)-allosamizoline aminocyclopentitol was prepared by use of a route featuring pyridinium salt photochemical synthesis of the aminocyclopentene core, enzymatic desymmetrization, Wittig rearrangement to introduce the hydroxymethyl side chain, and regiocontrolled epoxide ring opening.