Haifeng Xiang

Tunable Fluorescent/Phosphorescent Platinum(II) Porphyrin–Fluorene Copolymers for Ratiometric Dual Emissive Oxygen Sensing

A series of new platinum(II) 5,15-bis(pentafluorophenyl)-10,20-bis(phenyl)porphyrin-9,9-dioctylfluorene copolymers, in which the relative intensities of the blue fluorescence and red phosphorescence can be easily tuned by the initial feed ratio of the two monomers or energy transfer between the fluorescent and phosphorescent units, have been designed and prepared for the application in ratiometric dual emissive oxygen sensing. To the best of our knowledge, this is the first example of a ratiometric oxygen sensor based on dual fluorescent/phosphorescent polymers or copolymers containing transition-metal complexes. It also provides an alternative and easy way to achieve dual emissive oxygen sensing.

A high-performance organic field-effect transistor based on platinum(II) porphyrin: peripheral substituents on porphyrin ligand significantly affect film structure and charge mobility.

Organic field-effect transistors incorporating planar pi-conjugated metal-free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H2(OX)] (H(2)OX=etioporphyrin-I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H2TBP=tetra-(n-butyl)porphyrin) as determined by single crystal X-ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field-effect transistors (FETs) made from thin films of all these metal-free macrocycles and their metal derivatives show a p-type semiconductor behavior with a charge mobility (mu) ranging from 10(-6) to 10(-1) cm(2) V(-1) s(-1). Annealing the as-deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2 x 10(-1) cm(2) V(-1) s(-1), which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field-effect transistors made from thin films of metal-free macrocycles (except tetra-(n-propyl)porphycene) have significantly lower mu values (3.0 x 10(-6)-3.7 x 10(-5) cm(2) V(-1) s(-1)).

Optical Chemosensors Based on Transmetalation of Salen-Based Schiff Base Complexes

We report our systematic studies of novel, simple, selective, and sensitive optical (both colorimetric and fluorescent) chemosensors for detecting Al(3+) based on transmetalation reactions (metal displacement or exchange reactions) of a series of K(I), Ca(II), Zn(II), Cu(II), and Pt(II) complexes containing different ligands of salen-based Schiff bases. Both the chemical structure of the salen ligand and the identity of the central metal ion have a tremendous impact on the sensing performance, which is mainly determined by the stability constant of the complex. Moreover, the selectivities of the salen-complex-based chemosensors are much better than those of the corresponding free salen ligands because of the shielding function of the filled-in metal ion in the complex. Therefore, the present work potentially provides a new and simple way to design optical probes via complex-based transmetalation reactions.

Improving efficiency of organic photovoltaic cells with pentacene-doped CuPc layer

We have fabricated efficient heterojunction organic photovoltaic (OPV) cells based on pentacene-doped copper(II) phthalocyanine (CuPc) layer as donor and fullerene (C60) layer as acceptor. The power conversion efficiency of 4% pentacene-doped CuPc∕C60 OPV cell (3.06%) is increased by 77% compared with that of the standard CuPc∕C60 OPV cell (1.73%). The efficiency improvement can be attributed to the higher carrier mobility instead of the stronger photon absorption of the pentacene-doped CuPc layer.

Ratiometric fluorescent pH probes based on aggregation-induced emission-active salicylaldehyde azines

A series of luminescent salicylaldehyde azines (SAs) containing different electron-accepting substituents (–NO2, –F, and –Cl), electron-donating substituents (–OMe and –NEt2), and a π-extended system (naphthalene ring) are prepared for the application of fluorescent pH probes. These SAs inheriting the aggregation-induced emission (AIE) features display strong blue, green, and red fluorescence with large Stokes shifts in water and solid medium. Combining the advantages of AIE and the chemical reactivity of phenol towards OH−/H+, most of the SAs can be used as ratiometric fluorescent pH probes with a broad pH range (2–14) in water and solid medium (test paper). Moreover, the inherent relationship between their chemical structures and AIE properties/pKa values (7.5–13.3) is studied, which provides unequivocal insights into the design of AIE-active dyes and their applications.

Synthesis and photophysical properties of water-soluble sulfonato-Salen-type Schiff bases and their applications of fluorescence sensors for Cu2+ in water and living cells

A series of water-soluble sulfonato-Salen-type ligands derived from different diamines including 1,2-ethylenediamine (Et-1-Et-4), 1,2-cyclohexanediamine (Cy-1 and Cy-2), 1,2-phenylenediamine (Ph-1-Ph-3 and PhMe-1-PhMe-4), and dicyano-1,2-ethenediamine (CN-1) has been designed and prepared. Sulfonate groups of ligands ensure good stability and solubility in water without affecting their excited state properties. These ligands exhibit strong UV/Vis-absorption and blue, green, or orange fluorescence. Time-dependent-density functional theory calculations have been undertaken to reveal the influence of ligand nature, especially sulfonate groups, on the frontier molecular orbitals. Since their fluorescence is selectively quenched by Cu(2+), the sulfonato-Salen-type ligands can be used as highly selective and sensitive turn-off fluorescence sensors for the detection of Cu(2+) in water and fluorescence imaging in living cells.

Efficient white and red light emission from GaN/tris-(8-hydroxyquinolato) aluminum/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin hybrid light-emitting diodes

We report efficient white and red light emission from GaN light-emitting diode (LED)/tris-(8-hydroxyquinolato) aluminum (Alq3)/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin (PtF20TPP) hybrid LEDs. Alq3 was employed to enhance the efficiency of red and white luminescence conversion (LC) LEDs through energy transfer from Alq3 to PtF20TPP. In the white LC-LED, an intense, highly pure white-light emission with CIE_1931 coordinates at x=0.32 and y=0.31 is obtained. The LC-LEDs in this work have relatively high efficiencies, 3.3% for white LC-LED and 4.0% for red LC-LED. The color temperature (Tc), color rendering index (Ra) and luminous efficiency (ηL) of the white LC-LED at 20 mA are 6800 K, 90.6 and 10 lm/W, respectively.

Highly Enantioselective Michael Addition of Malononitrile to Vinylogous Imine Intermediates Generated in situ from Arylsulfonyl Indoles

The conjugate addition of carbon-based nucleophiles to activated unsaturated systems represents one of the best established and most versatile carbon–carbon bond-forming reactions in organic chemistry. Malononitrile, a classic equivalent of a 1,3-dicarbonyl compound, might be a valuACHTUNGTRENNUNGable nucleophile, which can then be conveniently transformed into carboxylic acid, ester, amine, or amide groups. However, to the best of our knowledge, few studies of asymmetric Michael additions that use malononitrile as the nucleophile have been reported. Arylsulfonyl indoles 1, which bear a good leaving group, are an effective precursor for vinylogous imine intermedi-

Synthesis of 3-indole derivatives by copper sulfonato Salen catalyzed three-component reactions in water

An efficient three-component reaction of indole, aldehyde, and malononitrile in water catalyzed by a copper(II) sulfonato Salen complex afforded 3-indole derivatives in good to excellent yields up to 97%.

Palladium-Catalyzed CH ortho Arylation of Benzoic Acids with Diaryliodonium Salts in Water

Palladium-catalyzed C C bond-formation reactions between aryl halides or triflates and organometallic reagents are among the most useful methods to construct biaryls, which are usually structural motifs found in important nature products, pharmaceuticals, and organic materials. The corresponding organometallic nucleophilic starting materials, however, are often not commercially available and sometimes lead to the formation of undesired side products. Over the past decade, extensive efforts have been made to explore the transition-metal-catalyzed direct arylation of C H bonds as ecologically and economically friendly alternatives. Furthermore, owing to the requirement of site selectivity, directing groups such as pyridyl, acylamino, hydroxy, and phenolic ester groups have been broadly introduced into substrates. The majority of these directing groups cannot be easily removed from the products, and a few of them have to be deprotected by further transformations. In recent years, transition-metal-catalyzed decarboxylative coupling reactions have emerged as a powerful strategy to form carbon–carbon and carbon–heteroatom bonds from cheap, diverse, and readily available aryl carboxylic acids. The carboxylic acid group can efficiently be removed or converted into a variety of useful functional groups, which makes the directed ortho C H functionalization of carboxylic acids exceptionally practical for applications in organic synthesis. In 2007, the groups of Yu and Daugulis pioneered the direct ortho-arylation of benzoic acids with aryl halides by using palladium as a catalyst (Scheme 1 a). Also, Yu and co-workers demonstrated that phenylboronic acid esters and aryltrifluoroborates can be utilized as coupling partners for the ortho functionalization of benzoic acids (Scheme 1 b). 7] Recent work has identified that diaryliodonium salts, which are commercially available or easily synthesized, are important alternatives that can be used as arylation reagents in palladium-catalyzed C H arylation reactions. However, application of diaryliodonium salts in the catalytic ortho-arylation of benzoic acids has not yet been reported. The use of water as an environmentally benign, nonflammable, and nontoxic medium for organic transformations is strongly desired because of green chemistry. 10] As part of our continuous interest in aqueous catalysis, herein we report an efficient and practical protocol for the palladium-catalyzed C H ortho arylation of benzoic acids with diaryliodonium salts by using water as the solvent (Scheme 1 c). In our initial optimization study, m-toluic acid and phenyl(2,4,6-trimethylphenyl)iodonium triflate (2 a) were chosen as model substrates. As illustrated in Table 1, no desired product was found in the absence of catalyst by using water as the solvent (Table 1, entry 1). Gratifyingly, the substrates could be transformed into desired ortho-arylated product 3 a in 85 % yield by using a catalytic amount of Pd(OAc)2 (Table 1, entry 2). Next, a variety of organic solvents were tested; nevertheless, only a trace amount of the product was formed (Table 1, entries 3–10). The results suggest strongly that the choice of water as the solvent is crucial for this reaction. Replacing Pd(OAc)2 by PdCl2 resulted in a slightly lower yield of the product (78 %; Table 1, entry 11). Furthermore, low temperatures decelerated the reaction rate; product 3 a was obtained in 54 % yield if the reaction was performed at 80 8C (Table 1, entry 12). A symmetrical iodonium salt was also compatible with the reaction, and it provided a similar result (Table 1, entry 13). Scheme 1. Palladium-catalyzed C H ortho arylation of benzoic acids. Ac = acetyl, BQ = 1,4-benzoquinone, Mes = 2,4,6-trimethylphenyl, Tf = trifluoromethanesulfonyl.