Femtosecond dynamics of the ring closing process of diarylethene: a case study of electrocyclic reactions in photochromic single crystals

The cyclization reaction of the photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene was studied in its single crystal phase with femtosecond transient absorption spectroscopy. The transient absorption measurements were performed with a robust acquisition scheme that explicitly exploits the photoreversibility of the molecular system and monitors the reversibility conditions. The crystalline system demonstrated 3 × 10(4) repeatable cycles before significant degradation was observed. Immediately following photoexcitation, the excited state absorption associated with the open-ring conformation undergoes a large spectral shift with a time constant of approximately 200 fs. Following this evolution on the excited state potential energy surface, the ring closure occurs with a time constant of 5.3 ps, which is significantly slower than previously reported measurements for similar derivatives in the solution phase. Time resolved electron diffraction studies were used to further demonstrate the assignment of the transient absorption dynamics to the ring closing reaction. The mechanistic details of the ring closing are discussed in the context of prior computational work along with a vibrational mode analysis using density functional theory to give some insight into the primary motions involved in the ring closing reaction.     

DFT/TDDFT study on the electronic structures and optoelectronic properties of several red-emitting osmium(II) complexes with different P^P ancillary ligands

The ground and excited state geometries of several red-emitting phosphors (N^N)(2)Os(P^P) [where N^N = 5-(1-isoquinolyl)-1,2,4-triazoles, P^P = bis(dimethylphosphino)methylene(dmpm) (1); P^P = cis-1,2-bis-(dimethylphosphino)ethene(dmpe) (2); P^P = 1,2-bis(dimethylphosphino)benzene(dmpb) (3); P^P = 1,2-bis(dimethylphosphino)naphthalene(dmpn) (4); P^P = 1,2-bis(dimethylphosphino)-4-cyano-benzene(dmpcb) (5)] have been investigated by using the density functional theory (DFT) methods. The calculated results indicate that, for the studied complexes, the electron-transporting performance is better than the hole-transporting performance. The alteration of cis-P^P ancillary ligands with different conjugation lengths and substituents has an impact on the optoelectronic properties of these complexes, especially the electron-withdrawing group -CN in 5. The calculated energy gaps are nearly the same for complexes 1 to 4 (3.34 eV), while for 5, the HOMO and LUMO energies are lowered and the energy gap increases (3.42 eV). The absorption of 1 is red shifted, while that of 5 is blue shifted compared with the absorptions of 2, 3, and 4, which have similar absorptions. Complexes 2, 3, and 4 have almost identical emission wavelength 699 nm, while 1 (715 nm) and 5 (735 nm) are red shifted. The calculated electron affinities and reorganization energies indicate that complex 5 is the easiest for electron injection and has the best electron-transporting performance.     

One-pot microwave synthesis of water-dispersible, ultraphoto- and pH-stable, and highly fluorescent silicon quantum dots

Fluorescent silicon quantum dots (SiQDs) are facilely prepared via one-pot microwave-assisted synthesis. The as-prepared SiQDs feature excellent aqueous dispersibility, robust photo- and pH-stability, strong fluorescence, and favorable biocompatibility. Experiments show the SiQDs are superbly suitable for long-term immunofluorescent cellular imaging. Our results provide a new and invaluable methodology for large-scale synthesis of high-quality SiQDs, which are promising for various optoelectronic and biological applications.     

Novel electrochemical biosensor based on functional composite nanofibers for sensitive detection of p53 tumor suppressor gene

A novel electrochemical biosensor based on functional composite nanofibers for sensitive hybridization detection of p53 tumor suppressor using methylene blue (MB) as an electrochemical indicator is developed. The carboxylated multi-walled carbon nanotubes (MWNTs) doped nylon 6 (PA6) composite nanofibers (MWNTs–PA6) was prepared using electrospinning, which served as the nanosized backbone for pyrrole (Py) electropolymerization. The functional composite nanofibers (MWNTs–PA6–PPy) used as supporting scaffolds for ssDNA immobilization can dramatically increase the amount of DNA attachment and the hybridization sensitivity. The biosensor displayed good sensitivity and specificity. The target wild type p53 sequence (wtp53) can be detected as low as 50 fM and the discrimination is up to 57.5% between the wtp53 and the mutant type p53 sequence (mtp53). It holds promise for the early diagnosis of cancer development and monitoring of patient therapy.     

Mechanism of Ketone Allylation with Allylboronates as Catalyzed by Zinc Compounds: A DFT Study

The mechanism of the allylation reaction between 4‐chloroacetophenone and pinacol allylboronates catalyzed by ZnEt₂ with alcohols was investigated using density functional theory (DFT) at the M05‐2X/6‐311++G(d,p) level. The calculations reveal that the reaction prefers to proceed through a double γ‐addition stepwise reaction mechanism rather than a Lewis acid‐catalyzed concerted one. The intermediate with a four‐coordinated boron center, which is formed through proton transfer from EtOH to the ethyl group of ZnEt₂ mediated by the boron center, is the active species and an entrance for the catalytic cycle. The latter is composed of three elementary steps: 1) boron to zinc transmetalation leading to the formation of allylzincate species, 2) electrophilic addition of ketone to allylzincate species, and 3) generation of the final product with recovery of the catalyst. The boron to zinc transmetalation step has the largest energy barrier of 61.0 kJ mol^?1 and is predicted to be the rate‐determining step. The calculations indicate that the additive EtOH plays important roles both in lowering the activation free energy for the formation of the four‐coordinated boron active intermediate and in transforming the low catalytic activity ZnEt₂ into high activity zinc alkoxide species. The alcohols with a less sterically encumbering R group might be the effective additives. The substituted groups on the allylboronates might primarily affect the boron to zinc transmetalation, and the allylboronates with substituents on the C_γ atom is poor in reactivity. The comparison of the catalytic effect between the zinc compounds investigated suggest that Zn(OEt)₂, Zn(OH)₂, and ZnF₂ exhibit higher catalytic efficiency for the boron to zinc transmetalation due to the activation of the B? C_α bond through orbital interactions between the p orbitals of the EtO, OH, F groups and the empty p orbital of the boron center.     

Fluorescent Protein Capped Mesoporous Nanoparticles for Intracellular Drug Delivery and Imaging

A multifunctional system for intracellular drug delivery and simultaneous fluorescent imaging was constructed by using histidine‐tagged, cyan fluorescent protein (CFP)‐capped magnetic mesoporous silica nanoparticles (MMSNs). This protein‐capped multifunctional nanostructure is highly biocompatible and does not affect cell viability or proliferation. The CFP acts not only as a capping agent, but also as a fluorescent imaging agent. The nanoassembly was activated by histidine‐based replacement, leading to release of drug molecules encapsulated in the nanopores into the bulk solution. The fluorescent imaging functionality would allow noninvasive tracking of the nanoparticles in the body. By combining the drug delivery with cell‐imaging capability, these nanoparticles may provide valuable multifunctional nanoplatforms for biomedical applications.     

A novel technology for the detection, enrichment, and separation of trace amounts of target DNA based on amino-modified fluorescent magnetic composite nanoparticles

A novel, highly sensitive technology for the detection, enrichment, and separation of trace amounts of target DNA was developed on the basis of amino-modified fluorescent magnetic composite nanoparticles (AFMN). In this study, the positively charged amino-modified composite nanoparticles conjugate with the negatively charged capture DNA through electrostatic binding. The optimal combination of AFMN and capture DNA was measured by dynamic light scattering (DLS) and UV–vis absorption spectroscopy. The highly sensitive detection of trace amounts of target DNA was achieved through enrichment by means of AFMN. The detection limit for target DNA is 0.4 pM, which could be further improved by using a more powerful magnet. Because of their different melting temperatures, single-base mismatched target DNA could be separated from perfectly complementary target DNA. In addition, the photoluminescence (PL) signals of perfectly complementary target DNA and single-base mismatched DNA as well as the hybridization kinetics of different concentrations of target DNA at different reaction times have also been studied. Most importantly, the detection, enrichment, and separation ability of AFMN was further verified with milk. Simple and satisfactory results were obtained, which show the great potential in the fields of mutation identification and clinical diagnosis.     

A novel method to prepare polymer-ionic liquid gel under high pressure and its electrochemical properties

Sol–gel transition behavior of ionic liquid gel based on poly (ethylene glycol) (PEG) and ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO₄] has been investigated under the pressure up to 250 MPa. The Temperature versus Pressure phase diagram of PEG/[EMIM][EtSO₄] gel is constructed, and it indicates that the melting point is an increasing function of pressure. Based on the phase diagram, the PEG/[EMIM][EtSO₄] gels are prepared by cooling under the pressure of 300 MPa and atmospheric pressure, respectively. From the differential scanning calorimetry result of the recovered samples, it is found that PEG/[EMIM][EtSO₄] gel prepared under high pressure has a higher crystallinity and smaller crystal size polymer network, comparing with under atmospheric pressure. The cyclic voltammograms and impedance spectra tests indicate that the PEG/[EMIM][EtSO₄] gel prepared under high pressure exhibit higher ionic conductivity comparing with atmospheric pressure. It could be speculated these excellent properties might be attributed to the loose gel structure and high ionic density induced by high pressure.