Syntheses of Dihydropyrene–Cyclophanediene Negative Photochromes Containing Internal Alkenyl and Alkynyl Groups and Comparison of Their Photochemical and Thermochemical Properties

Synthesis of a variety of 8,16-disubstituted-<i>anti</i>-[2.2]­metacyclophanedienes (CPD) with alkenyl and alkynyl internal (8,16) groups is described together with their analogous dihydropyrenes (DHP). Eyring and Arrhenius parameters were determined for the thermal closing reaction, CPD to DHP, and half-lives at 20 °C were found to range from 11 days (X = CHO) to 36 years (X = CN), with alkenyl functions being from 56 days to 10 years. The visible light opening reaction, DHP to CPD, showed relative rates of 1 (X = CN) to 240 (X = CHCMe₂)

Density Functional Theory Study of Poly(<i>o</i>‑phenylenediamine) Oligomers

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed to gain insight into the structure of poly­(<i>o</i>-phenylenediamine) (POPD). Both reported structures of POPD, ladder (L)- and polyaniline (P)-like, are investigated theoretically through the oligomers approach. The simulated vibrational properties of 5POPD­(L) and 5POPD­(P) at B3LYP/6-31G (d) along with their assignments are correlated with experimental frequencies. Vibrational spectra show characteristic peaks for both POPD­(L) and POPD­(P) structures and do not provide any conclusive evidence. Excited-state properties such as band gap, ionization potential, electron affinities, and HOMO–LUMO gaps of POPD­(L) and POPD­(P) from monomers to five repeating units are simulated. UV–vis spectra are simulated at the TD-B3LYP/6-31+G (d, p) level of theory, supportive to the ladder-like structure as the major contributor. Comparison of the calculated data with the experimental one strongly suggests that the ladder-like structure is the predominant contributor to the molecular structure of POPD; however, a small amount of POPD­(P) is also believed to be present

DFT Study of Polyaniline NH₃, CO₂, and CO Gas Sensors: Comparison with Recent Experimental Data

Density functional theory studies (DFT) have been carried out to evaluate the ability of polyaniline emeraldine salt (PANI ES) from 2 to 8 phenyl rings as sensor for NH₃, CO₂, and CO. The sensitivity and selectivity of <i>n</i>PANI ES among NH₃, CO₂, and CO are studied at UB3LYP/6-31G­(d) level of theory. Interaction of <i>n</i>PANI ES with CO is studied from both O (CO(1)) and C (CO(2)) sides of CO. Interaction energy, NBO, and Mulliken charge analysis were used to evaluate the sensing ability of PANI ES for different analytes. Interaction energies are calculated and corrected for BSSE. Large forces of attraction in <i>n</i>PANI ES-NH₃ complexes are observed compared to <i>n</i>PANI ES–CO₂, <i>n</i>PANI ES-CO(1), and <i>n</i>PANI ES-CO(2) complexes. The inertness of ⁺CO^– in <i>n</i>PANI ES-CO(1) and <i>n</i>PANI ES-CO(2) complexes are also discussed. Frontier molecular orbitals and energies indicate that NH₃ changes the orbital energy of <i>n</i>PANI ES to a greater extent compared to CO₂, CO(1), and CO(2). Peaks in UV–vis and UV–vis–near-IR spectra of <i>n</i>PANI ES are blue-shifted upon doping with NH₃, CO₂, CO(1), and CO(2) which illustrates dedoping of PANI ES to PANI emeraldine base (PANI EB). Finally, it is concluded that PANI ES has greater response selectivity toward NH₃ compared to CO₂ and CO and it is consistent with the experimental observations

Doping and Dedoping Processes of Polypyrrole: DFT Study with Hybrid Functionals

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the UB3LYP/6-31G­(d) level have been performed to investigate the tunable nature, i.e., doping and dedoping processes, of polypyrrole (PPy). The calculated theoretical data show strong correlation with the recent experimental reports, which validates our computational protocol. The calculated properties are extrapolated to the polymer (PPy) through a second-order polynomial fit. Changes in band gap, conductivity, and resistance of <i>n</i>Py and <i>n</i>Py-X (where <i>n</i> = 1–9 and X = +, NH₃, and Cl) were studied and correlated with the calculated vibrational spectra (IR) and electronic properties. Upon doping, bridging bond distance and internal bond angles decrease (decrease in resistance over polymer backbone), whereas dedoping results in increases in these geometric parameters. In the vibrational spectrum, doping is characterized by an increase in the band peaks in the fingerprint region and/or red shifting of the spectral bands. Dedoping (9Py⁺ with NH₃), on the other hand, results in decreases in the number of vibrational spectral bands. In the UV–vis and UV–vis–near-IR spectra, the addition of different analytes (dopant) to 9Py results in the disappearance of certain bands and gives rise to some new absorbances corresponding to localized and delocalized polaron bands. Specifically, the peaks in the near-IR region at 1907 nm for Py⁺ and 1242 nm for 9Py-Cl are due to delocalized and localized polaron structures, respectively. Upon p-doping, the band gaps and resistance of <i>n</i>Py decrease, while its conductivity and π-electron density of conjugation increase over the polymeric backbone. However, a reversal of properties is obtained in n-doping or reduction of <i>n</i>Py⁺. In the case of oxidation and Cl dopant, the IP and EA increase, and consequently, there is a decrease in the band gap. NBO and Mulliken charges analyses indicate charge transferring from the polymer in the case of p-type dopants, while this phenomenon is reversed with n-type dopants

Internal B ← O Bond Facilitated Photo/Thermal Isomerization of Tetra-Coordinated Boranes

A new series of O∧C-chelate tetra-coordinated boranes with naphtha-aldehyde as the chelate backbone have been synthesized. Their photophysical and photochemical properties have been examined, which show that all of the compounds can undergo both photo and thermal transformations, generating aryl-migrated [1,2]oxaborinine derivatives as the major products. 1,3-Sigmatropic shifts and an intramolecular nucleophilic addition mechanism are proposed for the photochemical and thermal conversion pathways, respectively

A new rosane-type diterpenoid from <i>Stachys parviflora</i> and its density functional theory studies

<div><p>A new rosane-type diterpenoid (<b>1</b>) has been isolated from the chloroform fraction of <i>Stachys parviflora</i>. Structure of <b>1</b> was proposed based on 1D and 2D NMR techniques including correlation spectroscopy, heteronuclear multiple quantum coherence, heteronuclear multiple bond correlation and nuclear Overhauser effect spectroscopy. A theoretical model for the electronic and spectroscopic properties of compound <b>1</b> is also developed. The geometries and electronic properties were modelled at B3LYP/6-31G^* and the theoretical scaled spectroscopic data correlate nicely with the experimental data.</p></div

Molecular and Electronic Structure Elucidation of Polypyrrole Gas Sensors

Sensitivity and selectivity of polypyrrole (PPy) toward NH₃, CO₂, and CO have been studied at density functional theory (DFT). PPy oligomers are used both in the doped (PPy⁺) and neutral (PPy) form for their sensing abilities to realize the best state for gas sensing. DFT calculations are performed at the hybrid functional, B3LYP/6-31G­(d), level of theory. Detection/interaction of CO is investigated from carbon [CO(1)] and oxygen termini of CO [CO(2)]. Interaction energies and charge transfer are simulated which reveal the sensing ability of PPy toward these gases. Furthermore, these results are supported by frontier molecular orbital energies and band gap calculations. PPy, in both the doped and neutral state, is more sensitive to NH₃ compared to CO₂ and CO. More interestingly, NH₃ causes doping of PPy and dedoping of PPy⁺, providing evidence that PPy/PPy⁺ is an excellent sensor for NH₃ gas. UV–vis and UV–vis–near-IR spectra of <i>n</i>Py, <i>n</i>Py⁺, and <i>n</i>Py/<i>n</i>Py⁺–X complexes demonstrate strong interaction of PPy/PPy⁺ with these atmospheric gases. The better response of PPy/PPy⁺ toward NH₃ is also consistent with the experimental observations

NMR data

NMR data can be viewed in Bruker TopSpin Softwar

Decorating Mg₁₂O₁₂ Nanocage with Late First-Row Transition Metals To Act as Single-Atom Catalysts for the Hydrogen Evolution Reaction

In the pursuit of sustainable clean energy sources, the hydrogen evolution reaction (HER) has attained significant interest from the scientific community. Single-atom catalysts (SACs) are among the most promising candidates for future electrocatalysis because they possess high thermal stability, effective electrical conductivity, and excellent percentage atom utilization. In the present study, the applicability of late first-row transition metals (Fe-Zn) decorated on the magnesium oxide nanocage (TM@Mg12O12) as SACs for the HER has been studied, via density functional theory. The late first-row transition metals have been chosen as they have high abundance and are relatively low-cost. Among the studied systems, results show that the Fe@Mg12O12 SAC is the best candidate for catalyzing the HER reaction as it exhibits the lowest activation barrier for HER. Moreover, Fe@Mg12O12 shows high stability (Eint = −1.64 eV), which is essential in designing SACs to prevent aggregation of the metal. Furthermore, the results of the electronic properties’ analysis showed that the HOMO–LUMO gap of the nanocage is decreased significantly upon doping of Fe (from 4.81 to 2.28 eV), indicating an increase in the conductivity of the system. This study highlights the potential application of the TM@nanocage SAC systems as effective HER catalysts

Revised-Acridine-Thiosemicarbazones _NMR spectra and other from Novel acridine-based thiosemicarbazones as ‘turn-on' chemosensors for selective recognition of fluoride anion: aspectroscopic and theoretical study

DOI: https://doi.org/10.5061/dryad.9nq2kc4/