Chun-Hu Xu

Porous Single‐Crystalline Palladium Nanoparticles with High Catalytic Activities

Palladiums pore cousin: a facile approach is described for the size-controlled preparation of porous single-crystalline Pd nanoparticles. These porous Pd nanoparticles exhibit size-independent catalytic activities for the Suzuki coupling and are more active than commercial Pd/C catalysts.

Luminescence Modulation of Ordered Upconversion Nanopatterns by a Photochromic Diarylethene: Rewritable Optical Storage with Nondestructive Readout

[*] Prof. C.-H. Yan, C. Zhang, H.-P. Zhou, L.-Y. Liao, Dr. W. Feng, Dr. W. Sun, Dr. Z.-X. Li, C.-H. Xu, Dr. C.-J. Fang, Prof. L.-D. Sun, Prof. Y.-W. Zhang Beijing National Laboratory for Molecular Sciences State Key Laboratory of Rare Earth Materials Chemistry and Applications PKU-HKU Joint Laboratory on Rare Earth Materials and Bioinorganic Chemistry Peking University Beijing 100871 (P. R. China) E-mail: yan@pku.edu.cn

A Fluorescent‐Switch‐Based Computing Platform in Defending Information Risk

A molecular computing platform to defend against illegal information theft and invasion is obtained by the rational control of chemical reaction sequences in a newly prepared multiswitchable fluorophore 2-(4-aminophenylethylyl)-5-methoxy-2-(2-pyridyl)thiazole. Some of the fluorescent states with distinct recognition features are only activated through input-sequence-sensitive conversions. Chemically encoded user identity information can then be transmitted from a sequential logic unit to a combinational logic circuit, and hence, result in user-specific digital functionalities. The users password entry is authorized prior to each computing step to check not only the users identity, but also to reconfigure the molecular platform from the standby state to the corresponding operational state. Illegal accesses to the molecular computing platform are unable to activate the operation of the trusted users due to the incorrect activation processes, thereby ensuring the information is secured against information invasions.

New TTF derivatives: several molecular logic gates based on their switchable fluorescent emissions

The new redox-fluorescence dependent molecules MTs were synthesized with tetrathiafulvalene (TTF) and 5-methoxy-2-pyridylthiazoles coupled directly and rigidly. The fluorescent emission of MTs can be reversibly switched on/off depending on the oxidation states of the TTF unit, due to the peculiar property of TTF being oxidized reversibly and selectively. The dicationic MTs display a strong emission in the visible region and can be quenched by various chemical inputs. Based on this switchable fluorescent property of MTs, several logic gates such as AND, OR, NOT, NOR, INHIBIT, XNOR and NAND were realized by purposely selecting the initial states and chemical inputs.

Logic circuits constructed with an ion-sensitive fluorescent molecule 1,2-di[5-methoxy-2-(2-pyridyl)thiazoyl]ethyne

The fluorescence behaviours of a chemical-sensitive fluorescent molecule 1,2-di[5-methoxy-2-(2-pyridiyl)thiazoyl]ethyne (DMPTE) at different protonation and coordination states were studied. Upon addition of protons, metal ions and other chemicals, the fluorescent states can be switched reversibly. On the basis of the changes of fluorescence output signals from particular wavelengths in response to different combination sets of two particular external stimuli, the entire set of 2-bit Boolean binary logic functions were realized at the molecular level, including PASS 0, PASS 1, YES, NOT, OR, NOR, INHIBIT, IMPLICATION, AND, NAND, XOR, XNOR, and different logic functions were integrated reconfigurably within DMPTE. Besides, starting from the same initial state, a series of three-input logic gates and circuits were also constructed. Furthermore, the stepwise recognition process of DMPTE to different chemical input signals can also be utilized to distinguish different input sequences, thus a molecular keypad lock that authenticates three-digit password entries is indicated.

An enhanced fluorescence in a tunable face-to-face π⋯π stacking assembly directed by the H-bonding

A simple anthryl derivative 1-((anthracen-10-yl)methylene)-4-ethylthiosemicarbazide (ANS) shows a methanol-tunable solid state fluorescence enhancement based on different molecular packing structure; the emission is stronger in crystal 2 than that in crystal 1 under the same condition. This is mainly due to the formation of face-to-face π⋯π stacking assembly in crystal 2 which is directed and enhanced by intermolecular H-bonding interactions. The observation of fluorescence decay corroborates the formation of an emissive excimer in the π⋯π stacking assembly.

Intramolecular Charge Transfer in 5-Methoxy-2-(2-pyridyl)thiazole-Derived Fluorescent Molecules with Different Acceptor or Donor Substituents

On the basis of the rational derivation of 5-methoxy-2-(2-pyridyl)thiazole (2-MPT), we synthesized a new series of charge-transfer-based fluorescent molecules bearing different electronic donors or acceptors. The substituents range from strong electronic donors (e.g., amino and hydroxyl groups) to weak donating groups (e.g., proton and methyl groups) and electronic acceptors (e.g., pyridine ring). Through systematic investigation on the substituent-/polarity-dependent spectra (including room-temperature absorption, room-/low-temperature steady-state fluorescence spectra, and transient fluorescence lifetime characterization) and theoretical calculations, the emission properties of MPT derivatives are found to be governed by the rotation of the substituent around the triple bond axis, which produces distinct intramolecular charge transfer processes in either the twisted or planar excited states. The interconversion of excited-state geometry triggered by local interactions in polar solvents may produce a bathochromic shift of approximately 100 nm in fluorescence spectra. The solution state may also affect the ground- and excited-state conformation and hence results in the solvent-frozen-point sensitive fluorescence for some of the as-prepared molecules.

Solvent-sensitive charge-transfer absorption behaviours and dual-emissive fluorescent properties of a thiazole-conjugated pyridinium complex

A new fluorophore, 1-(ethoxy-carbonyl-methyl)-4-[2-(5-methoxy)thiazolyl]pyridinium bromide (4-MeB), has been synthesized and its photophysical properties investigated. In solvents with a larger dielectric constant (e), 4-MeB is ionized into free ions, showing a characteristic thiazolyl-pyridinium cation-centered π→π* electronic transition absorption band in the UV region. In solvents with smaller e values, such as tetrahydrofuran (THF), 1,4-dioxane (dioxane) and ethyl acetate (EtOAc), 4-MeB exists in the form of a tight ion pair, and concomitantly displays characteristic bromide anion-dependent absorption in the visible and UV regions. Among several other anions, such as PF6−, I− and Cl−, and neutral electron donor Et3N, only I− shows a similar influence on the absorption spectrum of 4-Me++ to that of bromide anion, confirming the bromide-dependent spectral properties of 4-MeB. With the help of theoretical calculations, the absorption in visible region is attributed to the charge-transfer from bromide anion to thiazolyl-pyridinium cation, which is tuned by the distance between the bromide anion and the thiazolyl-pyridyl moiety. In all of the solvents employed, 4-MeB also exhibits a dual-emissive fluorescent property, and the position of its emission peak is influenced by the excitation wavelength.