The separation of ethane from its analogous ethylene is of great importance in the petrochemical industry, but very challenging and energy intensive. Adsorptive separation using CH-selective porous materials can directly produce high-purity CH in a single operation but suffers from poor selectivity. Here, we report an approach to boost the separation of CH over CH, involving the control of pore structures in two isoreticular ultramicroporous metal-organic framework (MOF) materials with weakly polar pore surface for strengthened binding affinity toward CH over CH. Under ambient conditions, the prototypical compound shows a very small uptake difference and selectivity for CH/CH, whereas its smaller-pore isoreticular analogue exhibits a quite large uptake ratio of 237% (60.0/25.3 cm cm), remarkably increasing the CH/CH selectivity. Neutron powder diffraction studies clearly reveal that the latter material shows self-adaptive sorption behavior for CH, which enables it to continuously maintain close van der Waals contacts with CH molecules in its optimized pore structure, thus preferentially binds CH over CH. Gas sorption isotherms, crystallographic analyses, molecular modeling, selectivity calculation, and breakthrough experiment comprehensively demonstrate this unique MOF material as an efficient CH-selective adsorbent for CH purification.

Theoretical approaches addressing the mechanism of polymer crystallization remain the great challenge in polymer science. Numerous different, or even conflicting, models/theories have been proposed during the past several decades. However, none of them can fully satisfy the whole community. In this Perspective, we first trace the roots of these models/ theories back to the classical and nonclassical nucleation theories. The correlation between these theories and milestone theoretical works in polymer crystallization is elucidated together with their intrinsic drawbacks. Then the newly proposed two-step nucleation scenarios, with either bondorientational order or density fluctuation as precursors, are introduced, which, in our view, may stimulate the development of polymer crystallization theory. Afterward, the peculiarities of polymer crystallization due to chain flexibility and connectivity are discussed. A personal outlook on the ultimate polymer crystallization theory is given at last, which is suggested to address the following three questions: (i) How do flexible chains transform into rigid conformational ordered segments? (ii) How do interlamellar amorphous layers form? (iii) Are polymer chains dragged by force to the growth front? Answering these questions may eventually end the tough journey for the establishment of polymer crystallization theory, though polymer crystallization never completes fully.

Two rhodamine-based chemosensors (1 and 2) were designed, and their sensing behavior toward metal ions was investigated by fluorescence spectroscopies. 1 and 2 achieved tuning the selectivity to Fe(III) and Cr(III) in 100% aqueous solution, whereas other ions including Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I) induced basically no spectral change, which constituted a Fe(III)-selective and a Cr(III)-selective fluorescent chemosensor, respectively.

Based on our previous Monte Carlo simulation model of electron interactions with solids, including cascade secondary electron production, in which an optical dielectric function was used to describe electron energy loss and the associated secondary electron excitation, we have systematically investigated secondary electron generation and emission for 19 metals. The calculated secondary yield curve for primary beam energy ranging from 100 eV to 2 keV was found to correspond with the experimental universal curve. The dependence of the secondary yield on the work function was studied numerically, leading to a remarkable scattered deviation from Baroody’s relationship. This deviation shows that the secondary yield relates to different aspects of behavior by electrons in a metal, such as the cascade production process, the stopping power and specific energy loss mechanism for a sample, and the dependence on the electron density of states. The results provide an explanation for the scattered data on the experimental yield versus the work function. The calculations indicate that the characteristic energy loss of primaries may result in a corresponding feature in the energy distribution of secondaries.

A fluorescent sensor, N-(quinolin-8-yl)-2-(quinolin-8-yloxy)acetamide (HL), based on 8-aminoquinoline and 8-hydroxyquinoline platforms has been synthesized. This sensor displays high selectivity and sensitive fluorescence enhancement to Cd(2+) in ethanol. Moreover, sensor HL can distinguish Cd(2+) from Zn(2+) via two different sensing mechanisms (photoinduced electron transfer for Cd(2+); internal charge transfer for Zn(2+)). The composition of the complex Cd(2+)/HL or Zn(2+)/L(-) has been found to be 1:1, based on the fluorescence/absorption titration and further confirmed by X-ray crystallography.

The synthesis and evaluation of a novel Schiff-base fluorescent probe L for detection of Al(3+) are described. The structure of L was determined by X-ray and other spectroscopic data. The fluorescent spectra changes and microscopy images show that indicator L is highly selective for Al(3+) not only in abiotic systems but also in living cells. Other metal ions failed to respond. The new probe could be used as an efficient tool for Al(3+) monitoring in the environment and biological systems.

In a study of the spectroscopic behavior of two Schiff base derivatives, salicylaldehyde salicylhydrazone (1) and salicylaldehyde benzoylhydrazone (2), Schiff base 1 has high selectivity for Zn(2+) ion not only in abiotic systems but also in living cells. The ion selectivity of 1 for Zn(2+) can be switched for Mg(2+) by swapping the solvent from ethanol-water to DMF (N,N-dimethylformamide)-water mixtures. Imine 2 is a good fluorescent probe for Zn(2+) in ethanol-water media. Many other ions tested, such as Li(+), Na(+), Al(3+), K(+), Ca(2+), Cr(3+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Cd(2+), Sn(2+), Ba(2+), Hg(2+), and Pb(2+), failed to induce any spectral change in various solvents. The selectivity mechanism of 1 and 2 for metal ions is based on a combinational effect of proton transfer (ESPT), C═N isomerization, and chelation-enhanced fluorescence (CHEF). The coordination modes of the complexes were investigated.

Six conformationally restricted BODIPY dyes with fused carbocycles were synthesized to study the effect of conformational mobility on their visible electronic absorption and fluorescence properties. The symmetrically disubstituted compounds (2, 6) have bathochromically shifted absorption and fluorescence spectral maxima compared to those of the respective asymmetrically monosubstituted dyes (1, 5). Fusion of conjugation extending rings to the α,β-positions of the BODIPY core is an especially effective method for the construction of boron dipyrromethene dyes absorbing and emitting at longer wavelengths. The fluorescence quantum yields Φ of dyes 1-6 are high (0.7 ≤ Φ ≤ 1.0). The experimental results are backed up by quantum chemical calculations of the lowest electronic excitations in 1, 2, 5, 6, and corresponding dyes of related chemical structure but without conformational restriction. The effect of the molecular structure on the visible absorption and fluorescence emission properties of 1-6 has been examined as a function of solvent by means of the recent, generalized treatment of the solvent effect, proposed by Catalán (J. Phys. Chem. B 2009, 113, 5951-5960). Solvent polarizability is the primary factor responsible for the small solvent-dependent shifts of the visible absorption and fluorescence emission bands of these dyes.