Amine‐Responsive Adaptable Nanospaces: Fluorescent Porous Coordination Polymer for Molecular Recognition

Flexible and dynamic porous coordination polymers (PCPs) with well‐defined nanospaces composed of chromophoric organic linkers provide a scaffold for encapsulation of versatile guest molecules through noncovalent interactions. PCPs thus provide a potential platform for molecular recognition. Herein, we report a flexible 3D supramolecular framework {[Zn(ndc)(o‐phen)]?DMF}_n (o‐phen=1,10‐phenanthroline, ndc=2,6‐napthalenedicarboxylate) with confined nanospaces that can accommodate different electron‐donating aromatic amine guests with selective turn‐on emission signaling. This system serves as a molecular recognition platform through an emission‐readout process. Such unprecedented tunable emission with different amines is attributed to its emissive charge‐transfer (CT) complexation with o‐phen linkers. In certain cases this CT emission is further amplified by energy transfer from the chromophoric linker unit ndc, as evidenced by single‐crystal X‐ray structural characterization.     

Efficient Solar Cells Sensitized by Porphyrins with an Extended Conjugation Framework and a Carbazole Donor: From Molecular Design to Cosensitization

Porphyrin dyes containing the carbazole electron donor have been designed and optimized by wrapping the porphyrin framework, introducing an additional ethynylene bridge to extend the wavelength range of light absorption, and further suppression of the dye aggregation by introducing additional alkoxy chains. Application of a cosensitization approach results in improved current density (J_sc) and open‐circuit voltage (V_oc) values, thus achieving the highest cell efficiency of 10.45 %. This work provides an effective combined strategy of molecular design and cosensitization for developing efficient dye‐sensitized solar cells (DSSCs). In addition, carbazole has been demonstrated to be a promising donor for porphyrin sensitizers.     

Reactions in Nitroimidazole Triggered by Low‐Energy (0–2 eV) Electrons: Methylation at N1‐H Completely Blocks Reactivity

Low‐energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4‐nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA. The remarkably rich chemistry of 4NI is completely blocked in 1‐methyl‐4‐nitroimidazole (Me4NI), that is, upon methylation of 4NI at the N1 site. These remarkable results have also implications for the development of nitroimidazole based radiosensitizers in tumor radiation therapy.     

Long‐Distance Electronic Energy Transfer in Light‐Harvesting Supramolecular Polymers

The efficient collection of solar energy relies on the design and construction of well‐organized light‐harvesting systems. Herein we report that supramolecular phenanthrene polymers doped with pyrene are effective collectors of light energy. The linear polymers are formed through the assembly of short amphiphilic oligomers in water. Absorption of light by phenanthrene residues is followed by electronic energy transfer along the polymer over long distances (>100 nm) to the accepting pyrene molecules. The high efficiency of the energy transfer, which is documented by large fluorescence quantum yields, suggests a quantum coherent process.     

Double‐Wall Carbon Nanotube–Porphyrin Supramolecular Hybrid: Synthesis and Photophysical Studies

Double‐wall carbon nanotubes (DWCNTs) with pyridyl units covalently attached to the external wall through isoxazolino linkers and carboxylic groups that have been esterified by pentyl chains are synthesized. The properties of these modified DWCNTs are then compared with an analogous sample based on single‐wall carbon nanotubes (SWCNTs). Raman spectroscopy shows the presence of characteristic radial breathing mode vibrations, confirming that the samples partly retain the integrity of the nanotubes in the case of DWCNTs, including the internal and external nanotubes. Quantification of the pyridyl content for both samples (DWCNT and SWCNT derivatives) is based on X‐ray photoelectron spectroscopy and thermogravimetric profiles, showing very similar substituent load. Both pyridyl‐containing nanotubes (DWCNTs and SWCNTs) form a complex with zinc porphyrin (ZnP), as evidenced by the presence of two isosbestic points in the absorption spectra of the porphyrin upon addition of the pyridyl‐functionalized nanotubes. Supramolecular complexes based on pyridyl‐substituted DWCNTs and SWCNTs quench the emission and the triplet excited state identically, through an energy‐transfer mechanism based on pre‐assembly of the ground state. Thus, the presence of the intact inner wall in DWCNTs does not influence the quenching behavior, with respect to SWCNTs, for energy‐transfer quenching with excited ZnP. These results sharply contrast with previous ones referring to electron‐transfer quenching, in which the double‐wall morphology of the nanotubes has been shown to considerably reduce the lifetime of charge separation, owing to faster electron mobility in DWCNTs compared to SWCNTs.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

The effects of ultrasound frequency and power on the activation energy in Si-KOH reaction system

The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz （interval by 20kHz） and 10-50W （interval by 10W）, respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate.     

X-Ray Crystallography and Free Energy Calculations Reveal the Binding Mechanism of A2A Adenosine Receptor Antagonists

We present a robust protocol based on iterations of free energy perturbation (FEP) calculations, chemical synthesis, biophysical mapping and X-ray crystallography to reveal the binding mode of an antagonist series to the A_2A adenosine receptor (AR). Eight A_2AAR binding site mutations from biophysical mapping experiments were initially analyzed with sidechain FEP simulations, performed on alternate binding modes. The results distinctively supported one binding mode, which was subsequently used to design new chromone derivatives. Their affinities for the A_2AAR were experimentally determined and investigated through a cycle of ligand-FEP calculations, validating the binding orientation of the different chemical substituents proposed. Subsequent X-ray crystallography of the A_2AAR with a low and a high affinity chromone derivative confirmed the predicted binding orientation. The new molecules and structures here reported were driven by free energy calculations, and provide new insights on antagonist binding to the A_2AAR, an emerging target in immuno-oncology.