Anion-π Interaction in a Diketopyrrolopyrrole Derivative.

In this work, an N-substituted diketopyrrolopyrrole (DPP) derivative Ph-DPP was synthesized, showing interaction toward Lewis alkaline anions such as F-. The typical electron-transfer-dominated anion-π interaction product Ph-DPP•- and unexpected isomer product i-Ph-DPP were both observed, and their formation mechanism was studied by density functional theory calculations, suggesting that a deprotonation initiation route is favored, which gives interesting insight for understanding the debatable role of F- in such non-covalent intermolecular interactions.

Triarylboron-Based High Photosensitive Probes for Apoptosis Detection, Tumor-Targeted Imaging, and Selectively Inducing Apoptosis of Tumor Cells by Photodynamics.

Herein, a series of triarylboron-based fluorescent probes were developed for distinguishing apoptosis from living cells and even necrosis. They also demonstrate high photosensitivity because they can produce detectable reactive oxygen species (ROS) under an ultra-low light power density (1.5 mW/cm2). By changing the peripheral groups to regulate the performance, we identified a multifunctional probe, TAB-6-amyl, which can be used not only for selectively imaging apoptosis but also for the targeted imaging of SKOV-3 cells in vitro and in vivo. It could further specifically induce the apoptosis of SKOV-3 cells under light irradiation. During the study, we also found that TAB-6-amyl can cross the blood-brain barrier (BBB). Therefore, another probe based on this kind of structure, TAB-5-M-1-cRGD, was constructed for the targeted imaging of brain glioma cells and inducing their apoptosis. This study offers some promising tools for apoptosis detection and tumor photodynamic therapy (PDT).

Ratiometric dual fluorescence tridurylboron thermometers with tunable measurement ranges and colors.

Noncontact ratiometric fluorescent thermometers have received great interests in recent years. Besides being a sensitive and easily observable detection signal, the ratiometric dual fluorescence are also highly accurate and resistable to interference. However, organic molecular thermometers with such fluorescence property are very rare, and their measurement ranges and colors are limited. In this work, a series of ratiometric dual fluorescent tridurylboron thermometers, with tunable measurement ranges and colors, are designed and synthesized. The measurement ranges of the thermometers are -20 °C-40 °C, -10 °C-50 °C and -25 °C-30 °C in solid polymeric systems, and -50 °C-100 °C and -30 °C-110 °C in liquid organic solvent. With decreasing temperature, the fluorescence colors of tridurylboron-MOE thermometers are from green yellow to yellow red, green to green yellow, blue to green. This study provides a novel strategy for developing tunable ratiometric dual fluoresence organic molecular thermometers.

Insights into the Luminescence Thermochromism of a Triarylboron Derivative: The Role of Intramolecular Group Interaction.

The organic fluorescent probes for temperature have received increasing interest due to their extremely high spatial and temporal resolution. A few of triarylboron derivatives, as almost the only molecular probes consisting of a single luminophore, have the ability to change their luminescent color at different temperatures. The mechanism of their luminescence thermochromism is controversial. Herein, several spectral experiments, along with time-dependent density functional theory (TDDFT) and coupled-cluster (CC) calculations, are carried out to elucidate the temperature-dependent luminescence. The CC rather than the TDDFT methods give a relatively reasonable explanation for the experimental results. Consequently, the thermochromism is now considered as the result of conformational thermal equilibria that occur in both the excited and ground states. Besides, an unusual conformer with intramolecular excimer characteristic plays a crucial role in the attractive luminescence behavior.

Ultrasensitive reversible chromophore reaction of BODIPY functions as high ratio double turn on probe.

Chromophore reactions with changes to conjugation degree, especially those between the conjugated and unconjugated state, will bring a large spectral variation. To realize such a process, a meso-naked BODIPY (MNBOD) with two electron-withdrawing groups around the core is designed and synthesized. The resulting system is extremely sensitive to bases. The red, highly fluorescent solution readily becomes colorless and non-fluorescent after base addition; however, the color and fluorescence can be totally and instantly restored by addition of acid or formaldehyde. Analyses show that two identical MNBODs are connected by a C-C single bond (sp3) at the meso-position through a radical reaction that results in an unconjugated, colorless dimer complexed with bases. When the bases are consumed, the dimer immediately dissociates into the red, highly fluorescent, conjugated MNBOD monomer. With 260 nm spectral change and over 120,000 turn-on ratio, this chromophore-reaction can be utilized as a sensitive reaction-based dual-signal probe.

High-speed near-field photolithography at 16.85 nm linewidth with linearly polarized illumination.

Plasmonic focusing was investigated in concentric rings with a central pillar under linearly polarized illumination with a specific incident angle. When changing the incident angle of linearly polarized beam between 6 and 15 degree away from the normal direction, the focal spot size can keep a steady value of 37 nm, smaller than the focal spot with the radially polarized beam at the same excited condition, 45 nm. Combining this with the high-speed near-field photolithography technology, we demonstrated a plasmonic lithography with 16.85 nm linewidth on both organic and inorganic photo-resists in large scale at scanning speeds up to 11.3 m/s. This inclined linearly polarized illumination is easy to realize in a prototype of near-field photolithography system, and it opens a new cost effective approach towards the next generation lithography for nano-manufacturing.

Poly(naphthalene diimide) vinylene: solid state red emission and semiconducting properties for transistors.

In this work, a conjugated polymer PNV is developed, linking naphthalene diimide with a vinyl linkage. Owing to the C-HO hydrogen bond between the carbonyl and the vinyl, PNV exhibits a high red emission with a quantum yield of 33.4% in the solid state while it shows n-type properties with an electron mobility up to 1.5 × 10-3 cm2 V-1 s-1 in organic field effect transistors, simultaneously.

Thermally populated "bright" states for wide-range and high temperature sensing in air.

A series of air-stable triarylphosphine oxide-based thermosensitive ratiometric sensors based on local excited (LE) and charge transfer (CT) emissions have been designed and synthesized. The fluorescence intensity of tri(pyren-1-yl)phosphine oxide exhibits a prominent temperature-dependent feature over a wide temperature range due to thermally populated emissive LE states. The wide ratiometric temperature sensing range and high stability/reversibility in an ambient atmosphere indicate their great potentials in facile and practical applications.

Axially substituted phthalocyanine/naphthalocyanine doped in glass matrix: an approach to the practical use for optical limiting material.

A novel glass matrix doped with phthalocyanine or naphthalocyanine is prepared by a modified sol-gel technique. The photophysical and optical limiting properties of the phthalocyanine compounds both in glass matrix and in THF solution were investigated. The obtained glass matrix is homogeneous and transparent, as well as mechanically and thermodynamically stable enough to withstand very high laser fluence; the optical limiting performances of these compound samples are better than that of benchmark materials like C60 in toluene, carbon black in water, and graphene oxide in water or ethanol under nanosecond pulsed laser at 532 nm. Two prototypes of optical limiters doped in the glass matrix have very good optical limiting performances, which may provide potential practical use for optical limiting materials in a near future.

The steady flying of a plasmonic flying head over a photoresist-coated surface in a near-field photolithography system.

The near-field photolithography technique (NFPT) offers a new approach of nanolithography for a dramatic increase in the resolution with high throughput and low cost. The NFPT utilizes the same flight principle as that of the magnetic head of hard-disk drives but replacing the magnetic head with a plasmonic flying head. The plasmonic flying head, which can focus the incident laser beam to a spot size of sub-20 nm with an enhanced field intensity by exciting surface plasmon polaritons, takes off and then flies steadily above the revolving disk coated by a photoresist film to be patterned with a narrow gap of tens of nanometers. As a key foundation of the NFPT, the take off and flight stability of the plasmonic flying head affects the pattern density and the fabrication efficiency. This work proposed and investigated a molecular glass photoresist, named FPT-8Boc, for the large-scale consistent fabrication with the NFPT. To overcome the take-off problem of the head over the soft photoresist film, a transition zone is intentionally formed by washing off the coated photoresist in the outer area of the disk using a solvent. The simulation results by COMSOL Multiphysics software and quasi-Newton iteration method review that the matched transition zone height with spreading length can guarantee the flight stability of the plasmonic flying head on the soft photoresist. Using this method, a preliminary photolithography result with a 31 nm line width has been achieved.

Molecular Engineering of Aqueous Soluble Triarylboron-Compound-Based Two-Photon Fluorescent Probe for Mitochondria H2S with Analyte-Induced Finite Aggregation and Excellent Membrane Permeability.

Hydrogen sulfide (H2S) is a multifunctional signaling molecule that participates in many important biological processes. Herein, by functionalizing triarylboron with cyclen and diphenylamine, we synthesized TAB-1, TAB-2, and TAB-3 for H2S recongnization by rational design of molecular structures. Among them, aqueous soluble TAB-2 possesses excellent properties, including large two-photon action cross section, membrane permeability and can effectively complex with Cu(2+). The complex of TAB-2-Cu(2+) can selectively detect H2S with an instant response and mitochondria targeted. Moreover, the H2S-induced finite aggregation of indicators enhances their photostability and causes variation of the fluorescence lifetime. TAB-2-Cu(2+) has also been successfully applied for the mitochondria H2S imaging in NIH/3T3 fibroblast cells by TPM and FLIM.

In vivo observation of the pH alternation in mitochondria for various external stimuli.

The pH of mitochondria (pHm) has a close relationship with many biological processes. Here we developed a new indicator Mito-pH-1 for the ratiometric fluorescence detection of the mitochondria pH value, which has excellent tolerance to environmental change. And Mito-pH-1 has been used for the first time to monitor the change of pHm under temperature and H2O2 stimuli in living cells.

Intramolecular aggregation and optical limiting properties of triazine-linked mono-, bis- and tris-phthalocyanines.

A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized, intramolecular aggregation is found in bis- and tris-phthalocyanines via π-π stacking interaction. Theoretical and experimental studies reveal the formation of the intramolecular aggregation. The spectrographic, photophysical and nonlinear optical properties of these compounds are adjusted for the formation of the intramolecular aggregation. The bis-phthalocyanine dimer presents smaller fluorescence quantum yield, lower triplet formation yield and the triplet-minus-ground state extinction coefficient, which causes poorer optical limiting performance. It is interesting that the tris-phthalocyanine is composed of a mono-phthalocyanine part and a bis-phthalocyanine part, the optical limiting property of the tris-phthalocyanine is similar to that of mono-phthalocyanine.

Sensing for intracellular thiols by water-insoluble two-photon fluorescent probe incorporating nanogel.

A novel "turn-on" two-photon fluorescent probe containing a π-conjugated triarylboron luminogen and a maleimide moiety DMDP-M based on the photo-induced electron transfer (PET) mechanism for biothiol detection was designed and synthesized. By simply loading the hydrophobic DMDP-M on a cross-linked Pluronic(®) F127 nanogel (CL-F127), a probing system DMDP-M/CL-F127 was established, which shows quick response, high selectivity and sensitivity to cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in aqueous phase. The DMDP-M/CL-F127 system presented the fastest response to Cys with a rate constant of 0.56 min(-1), and the detection limit to Cys was calculated to be as low as 0.18 µM. The DMDP-M/CL-F127 system has been successfully applied to the fluorescence imaging of biothiols in NIH/3T3 fibroblasts either with single-photon or two-photon excitation because of its high biocompatibility and cell-membrane permeability. The present work provides a general, simple and efficient strategy for the application of hydrophobic molecules to sensing biothiols in aqueous phase, and a novel sensing system for intracellular biothiols fitted for both single-photon and two-photon fluorescence imaging.

Intracellular fluorescent temperature probe based on triarylboron substituted poly N-isopropylacrylamide and energy transfer.

A novel hydrophilic fluorescence temperature probe (PNDP) based on polarity-sensitive triarylboron compound (DPTB) and PNIPAM is designed and synthesized. In order to overcome the shortcomings of the single-intensity-based sensing mechanism and obtain more robust signals, ratiometric readout is achieved by designing an efficient FRET system (PNDP-NR) between DPTB and Nile Red (NR). PNDP-NR possesses some excellent features, including wide temperature range, good linear relationship, high temperature resolution, excellent reversibility, and stability. Within a sensing temperature range of 30-55 °C, the fluorescence color of PNDP-NR experiences significant change from red to green-blue. PNDP-NR is also introduced into NIH/3T3 cells to sense the temperature at the single-cell level. It gave excellent photostability and low cytotoxicity in vivo.

The effect of amphiphilic polymers on the association, morphology and photophysical properties of hypocrellin coordination polymer/fullerene assemblies.

The yttrium coordination polymer of pyrene modified hypocrellin A (Y(3+)-PyrHA) is synthesized and characterized. The methoxydiglycol malonate modified fullerene can be included in the cavity of Y(3+)-PyrHA in organic solution and buffer solution containing amphiphilic polymers, such as polyvinyl pyrrolidone (PVP), pluronic F127 and P123. The interaction between an amphiphilic polymer and Y(3+)-PyrHA plays an important role in controlling the size and morphology of Y(3+)-PyrHA/fullerene. TEM images of Y(3+)-PyrHA/fullerene in 1% F127 and P123 show nanoparticles in the size range 10-60 nm, while TEM images of Y(3+)-PyrHA/fullerene in 1% PVP display large-scale aggregation. Singlet oxygen is generated by irradiation of the polymer solution of Y(3+)-PyrHA/fullerene in the presence of oxygen. The electron paramagnetic resonance (EPR) spin trapping and 9,10-dimethoxyanthracene-2-sulfonic acid sodium salt (MAS) photooxidation results suggest that in 1% P123 solution Y(3+)-PyrHA/fullerene exhibits a higher singlet oxygen quantum yield than Y(3+)-PyrHA and the corresponding fullerene.

Water-soluble triarylboron compound for ATP imaging in vivo using analyte-induced finite aggregation.

Adenosine 5'-triphosphate (ATP) is a multifunctional molecule that participates in many important biological processes. Currently, fluorescence indicators for ATP with high performance are in demand. Reported herein is a novel water-soluble triarylboron compound which displays an apparent ATP-dependent fluorescence enhancement when dispersed in water. It can selectively recognize ATP from other bioactive substances in vitro and in vivo. The ATP-induced finite aggregation endows the indicator with appreciable photostability and superior tolerance to environmental electrolytes. This indicator has been successfully applied to the ATP imaging in NIH/3T3 fibroblast cells. The difference in the ATP levels within the membrane and cytosol is clearly visible.

A novel nanogel-based fluorescent probe for ratiometric detection of intracellular pH values.

A new nanogel indicator (NGI) for ratiometric fluorescent detection of intracellular pH values has been reported. In aqueous solution, the NGI can be used for ratiometric sensing of pH changes with a large hypsochromic shift of 100 nm in the green-red region and reversible. Furthermore, the NGI has been used to calibrate the cytosol pH value in living cells.

Two photon absorption energy transfer in the light-harvesting complex of photosystem II (LHC-II) modified with organic boron dye.

The plant light-harvesting complexes of photosystem II (LHC-II) play important roles in collecting solar energy and transferring the energy to the reaction centers of photosystems I and II. A two photon absorption compound, 4-(bromomethyl)-N-(4-(dimesitylboryl)phenyl)-N-phenylaniline (DMDP-CH2Br), was synthesized and covalently linked to the LHC-II in formation of a LHC-II-dye complex, which still maintained the biological activity of LHC-II system. Under irradiation with femtosecond laser pulses at 754 nm, the LHC-II-dye complex can absorb two photons of the laser light effectively compared with the wild type LHC-II. The absorbed excitation energy is then transferred to chlorophyll a with an obvious fluorescence enhancement. The results may be interesting and give potentials for developing hybrid photosystems.

A triarylboron-based fluorescent temperature indicator: sensitive both in solid polymers and in liquid solvents.

A novel triarylboron compound, MPB, exhibiting reversible thermochromic dual-fluorescence in solid-state polymers and in liquid solvents was designed and synthesized. The fluorescent solid-state polymer with MPB can serve as a highly sensitive self-reference temperature indicator with a concentration independent feature.