13 research outputs found
Syntheses of DihydropyreneâCyclophanediene 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]Âmetacyclophanedienes
(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
= CHî»CMe<sub>2</sub>)
Density Functional Theory Study of Poly(<i>o</i>âphenylenediamine) Oligomers
Density functional theory (DFT) and time-dependent DFT
(TD-DFT)
calculations have been performed to gain insight into the structure
of polyÂ(<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 5POPDÂ(L) and 5POPDÂ(P) at B3LYP/6-31G (d) along with
their assignments are correlated with experimental frequencies. Vibrational
spectra show characteristic peaks for both POPDÂ(L) and POPDÂ(P) structures
and do not provide any conclusive evidence. Excited-state properties
such as band gap, ionization potential, electron affinities, and HOMOâLUMO
gaps of POPDÂ(L) and POPDÂ(P) from monomers to five repeating units
are simulated. UVâvis 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 POPDÂ(P) is also believed to be present
DFT Study of Polyaniline NH<sub>3</sub>, CO<sub>2</sub>, 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 NH<sub>3</sub>, CO<sub>2</sub>,
and CO. The sensitivity and selectivity of <i>n</i>PANI
ES among NH<sub>3</sub>, CO<sub>2</sub>, and CO are studied at UB3LYP/6-31GÂ(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-NH<sub>3</sub> complexes are observed
compared to <i>n</i>PANI ESâCO<sub>2</sub>, <i>n</i>PANI ES-CO(1), and <i>n</i>PANI ES-CO(2) complexes.
The inertness of <sup>+</sup>CîŒO<sup>â</sup> 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 NH<sub>3</sub> changes the orbital energy of <i>n</i>PANI ES to a greater extent compared to CO<sub>2</sub>, CO(1), and
CO(2). Peaks in UVâvis and UVâvisânear-IR spectra
of <i>n</i>PANI ES are blue-shifted upon doping with NH<sub>3</sub>, CO<sub>2</sub>, 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 NH<sub>3</sub> compared to CO<sub>2</sub> 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/6-31GÂ(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> = 1â9 and X = +, NH<sub>3</sub>, 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<sup>+</sup> with
NH<sub>3</sub>), on the other hand, results in decreases in the number
of vibrational spectral bands. In the UVâvis and UVâvisânear-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<sup>+</sup> 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 Ï-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<sup>+</sup>. 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 â O Bond Facilitated Photo/Thermal Isomerization of Tetra-Coordinated Boranes
A new
series of Oâ§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<sup>*</sup> 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 NH<sub>3</sub>, CO<sub>2</sub>, and CO have been studied at density functional
theory (DFT). PPy oligomers are used both in the doped (PPy<sup>+</sup>) 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/6-31GÂ(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 NH<sub>3</sub> compared to CO<sub>2</sub> and
CO. More interestingly, NH<sub>3</sub> causes doping of PPy and dedoping
of PPy<sup>+</sup>, providing evidence that PPy/PPy<sup>+</sup> is
an excellent sensor for NH<sub>3</sub> gas. UVâvis and UVâvisânear-IR
spectra of <i>n</i>Py, <i>n</i>Py<sup>+</sup>,
and <i>n</i>Py/<i>n</i>Py<sup>+</sup>âX
complexes demonstrate strong interaction of PPy/PPy<sup>+</sup> with
these atmospheric gases. The better response of PPy/PPy<sup>+</sup> toward NH<sub>3</sub> is also consistent with the experimental observations
NMR data
NMR data can be viewed in Bruker TopSpin Softwar
Decorating Mg<sub>12</sub>O<sub>12</sub> 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 = â1.64 eV), which is essential
in designing SACs to prevent aggregation of the metal. Furthermore,
the results of the electronic propertiesâ analysis showed that
the HOMOâLUMO 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 âturn-on' chemosensors for selective recognition of fluoride anion: aspectroscopic and theoretical study
DOI: https://doi.org/10.5061/dryad.9nq2kc4/