Structure–Property Studies Toward the Stimuli-Responsive Behavior of Benzyl–Phospholium Acenes

A series of new phospholium acenes, quaternized with benzyl groups, was synthesized. Both different π-conjugated backbones and electron-donating/-withdrawing benzyl groups were systematically studied to reveal details on the nature of their structural dynamics. Extensive NMR studies (including variable concentration/temperature and 2D) suggested that the systems undergo <i>intramolecular</i> conformation changes in solution that are strongly affected by the electronic nature of the benzyl group, and thereby significantly affecting the phosphole-typical σ*−π* interaction. This class of “smart” phosphole system exhibits enhanced emission in the solid state and at low temperature in solution, due to aggregation-induced enhanced emission (AIEE). The dynamic features of these smart phospholes also endow the systems with external-stimuli (thermal and mechanical force) responsive photophysical properties. Crystallographic studies and theoretical calculations confirmed that the thermal response of the phospholium system is mainly due to the conformation changes in solution, while the mechanical response of the system can be attributed to both the <i>intramolecular</i> conformation and the <i>intermolecular</i> organization changes in the solid state

Computational Study on a HS^– Sensing Reaction Utilizing a Pyrylium Derivative

In this paper, we present a comprehensive computational study on the hydrogen sulfide sensing mechanism in aqueous solution using a pyrylium derivative. The possible sensing mechanisms were investigated under the neutral condition and acidic condition in the gas phase and in aqueous solution. The pyrylium–thiopyrylium transformation under the neutral condition is thermodynamically unfavorable, while it is greatly facilitated in the acidic condition catalyzed by a hydronium cation. In addition, the UV–vis absorption maxima of pyryliums and thiopyryliums were investigated at the TDDFT/B3LYP/6-31G+(d,p) level. The red shift of absorption maximum from unsubstituted pyrylium and thiopyrylium to dimethylamino-subisituted pyrylium and thiopyrylium as well as the red shift seen in the pyrylium–thiopyrylium transformation is interpreted in terms of the molecular orbital theory

Charge-Transfer Properties of Lateral Triphenylamine–Dithienophosphole Diads

Installation of an exocyclic triphenylamine group at the phosphorus center provides access to dithienophosphole materials with lateral charge-transfer (CT) ability. The degree of CT can be significantly manipulated not only via oxidation of the P-center but also surprisingly by alkylation of the 2,6-position of the scaffold

Molecular Engineering of the Physical Properties of Highly Luminescent π‑Conjugated Phospholes

The syntheses as well as detailed studies on the thermal, photophysical, and self-organization properties of a new series of phosphole-based ladder-type materials with exocyclic 5-alkylthienyl substituents are reported. The studies also include DFT calculations that provide support for the experimentally determined photophysics. In contrast to the related “phosphole-lipids” with fused conjugated head that exhibit low luminescence in solution but high luminescence in the solid state, the new system is highly luminescent in both solution and the solid state. The extensive structure–property study reported herein revealed that the physical properties of the new species can significantly be tuned via the size of the conjugated system of the head group, the functionalization of the phosphorus center, as well as the length of the thiophene-appended alkyl chain that impacts the intermolecular interactions via π–π stacking, ionic, and van der Waals interactions, respectively. This molecular engineering approach allows to access materials with intriguing properties that range from highly emissive oils to self-organized one-dimensional fibers

Structure–Property Studies of Bichromophoric, PAH-Functionalized Dithieno[3,2-<i>b</i>:2′,3′-<i>d</i>]phospholes

A series of dithienophospholes featuring polyaromatic hydrocarbon (PAH) substituents, with increasing number of fused rings ranging from 2 to 4 at the phosphorus center, have been synthesized and characterized. The installation of a large π-system in the vicinity of the dithienophosphole scaffold was found to induce unusual photophysics for this system that are based on the creation of two neighboring chromophores within the same molecular scaffold. Extensive photophysical studies revealed that significant energy transfer (ET) occurs from the PAH unit, which acts as a donor, to the dithienophosphole acceptor, showing ET efficiencies of almost 90%. TD-DFT calculations confirm the possibility for the two subunits to communicate with each other. Furthermore, due to the presence of the out-of-plane dithienophosphole unit, the PAH species do not show any significant tendency to form aggregates, such as excimers/exciplexes, even in colloidal suspensions

Charge-Transfer Properties of Lateral Triphenylamine–Dithienophosphole Diads

Installation of an exocyclic triphenylamine group at the phosphorus center provides access to dithienophosphole materials with lateral charge-transfer (CT) ability. The degree of CT can be significantly manipulated not only via oxidation of the P-center but also surprisingly by alkylation of the 2,6-position of the scaffold

Influence of pH on Ice Nucleation by Kaolinite: Experiments and Molecular Simulations

In mixed-phase or ice clouds, ice can be formed through heterogeneous nucleation. A major type of ice-nucleating particle (INP) in the atmosphere are mineral dust particles. For mixed-phase clouds, the pH of water droplets can vary widely and influence ice nucleation by altering the surface of some INPs, including mineral dust. Kaolinite is a commonly occurring clay mineral, and laboratory experiments, as well as molecular dynamics (MD) simulations, have demonstrated its ice-nucleating efficiency at neutral pH. We examine the influence of pH on the ice-nucleating efficiency of kaolinite, in the immersion freezing mode, through both droplet freezing experiments and MD simulations. Droplet freezing experiments using KGa-1b kaolinite samples are reported under both acidic (HNO3 solutions) and basic (NaOH solutions) conditions, covering the measured pH range 0.18–13.26. These experiments show that the ice-nucleating efficiency of kaolinite is not significantly influenced by the presence of acid but is reduced in extremely basic conditions. We report MD simulations aimed at gaining a microscopic understanding of the pH dependence of ice nucleation by kaolinite. The Al(001), Si(001), and three edge surfaces of kaolinite are considered, but ice nucleation was observed only for the Al(001) surface. The hydroxy groups exposed on the Al(001) surface can be deprotonated in a basic solution or dual-protonated in an acidic solution, which can influence ice nucleation efficiency. The protonation state of the Al(001) surface for a particular pH can be estimated using previously measured pKa values. We find that the monoprotonated Al(001) surface expected to be stable at near-neutral pH is the most effective ice-nucleating surface. In MD simulations, the ice nucleation efficiency persists for dual-protonation but decreases significantly with increasing deprotonation, qualitatively consistent with the experimental observations. Taken together, our experimental and MD results for a wide range of pH values support the suggestion that the Al(001) surface may be important for ice nucleation by kaolinite. Additionally, the deprotonation of hydroxy groups on INP surfaces can have a significant effect on their ice-nucleating ability

Origin of Enhanced Reactivity of a Microsolvated Nucleophile in Ion Pair S_N2 Reactions: The Cases of Sodium <i>p</i>‑Nitrophenoxide with Halomethanes in Acetone

In a kinetic experiment on the S_N2 reaction of sodium <i>p</i>-nitrophenoxide with iodomethane in acetone–water mixed solvent, Humeres et al. (<i>J. Org. Chem</i>. <b>2001</b>, <i>66</i>, 1163) found that the reaction depends strongly on the medium, and the fastest rate constant was observed in pure acetone. The present work tries to explore why acetone can enhance the reactivity of the title reactions. Accordingly, we make a mechanistic study on the reactions of sodium <i>p</i>-nitrophenoxide with halomethanes (CH₃X, X = Cl, Br, I) in acetone by using a supramolecular/continuum model at the PCM-MP2/6-311+G­(d,p)//B3LYP/6-311+G­(d,p) level, in which the ion pair nucleophile is microsolvated by one to three acetone molecules. We compared the reactivity of the microsolvated ion pair nucleophiles with solvent-free ion pair and anionic ones. Our results clearly reveal that the microsolvated ion pair nucleophile is favorable for the S_N2 reactions; meanwhile, the origin of the enhanced reactivity induced by microsolvation of the nucleophile is discussed in terms of the geometries of transition state (TS) structures and activation strain model, suggesting that lower deformation energies and stronger interaction energies between the deformed reactants in the TS lead to the lower overall reaction barriers for the S_N2 reaction of microsolvated sodium <i>p</i>-nitrophenoxide toward halomethanes in acetone

Molecular Engineering of Polyphosphazenes and SWNT Hybrids with Potential Applications as Electronic Materials

Polymer/single-walled carbon nanotube (SWNT) hybrids are promising candidates in applications such as flexible and stretchable electronics. In this contribution, we have examined structure–property relationships for constructing new polyphosphazene–SWNT hybrids. UV–vis and Raman spectroscopy studies revealed that the unique PN backbone enables strong intermolecular donor–acceptor interactions between the polymer and SNWTs. Furthermore, the polymeric backbone and the environment at the P-centers collectively play important roles in the formation of the hybrids. For polymers with shorter alkoxy substituents, the donor–acceptor interactions between the PN backbone and SWNTs play a crucial role in stabilizing the hybrid complexes, but for polymers with longer alkoxy substituents, the CH−π interactions and steric hindrance between the alkyl side chains and SWNTs counterbalance each other and control the stability of the hybrid complexes. Furthermore, the presence of fluorine and oxygen atoms is detrimental to the stability of the hybrid complexes. New cross-linkable polyphosphazenes with anthracene side units were also synthesized. When photo-cross-linked, these polyphosphazene/SWNT hybrids showed elastomeric characteristics and electronic properties that are promising for future applications

Removal of <i>p</i>‑Nitrophenol in Aqueous Solution by Mixed Fe⁰/(Passivated Fe⁰) Fixed Bed Filters

Fe⁰ particles were passivated by concentrated nitric acid, and a Fe⁰/(passivated Fe⁰) system was setup for <i>p</i>-nitrophenol (PNP) removal. First, the characteristics of passivated Fe⁰ particles were analyzed. The results suggest that the passivated Fe⁰ particles have an iron oxide passivation film on their surface with inertness and high electrode potential (0.57 V). Besides, the optimal conditions were obtained according to the significant parameters optimization. In addition, control experiments were set up to investigate the advantage of reactivity and operational life of the Fe⁰/(passivated Fe⁰) system, and the results confirmed that the new system had higher reactivity and longer operational life. Meanwhile, the reaction mechanism of Fe⁰/(passivated Fe⁰) system for PNP removal was proposed. Finally, with an analysis of preparation cost, the Fe⁰/(passivated Fe⁰) system could also be seemed as a cost-effective technology. Consequently, the developed Fe⁰/(passivated Fe⁰) system in this study is a promising technology for treatment of contaminated water