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The photochromic behavior of the fulgide molecule relies on ring-closure and ring-opening processes involving conical intersections during excited state transformation between isomers. The precise location and topography of these conical intersections significantly shape the decay process and fluorescence phenomena inherent to the molecule. This work combines electronic structure theory calculations using the density functional theory and wavefunction methods, as well as surface hopping simulation to analyze the photochemical behavior of an experimentally synthesized fulgide molecule, (E)-p-methylacetophenylisopropylidenesuccinic anhydride (1E). Our study reveals the conical intersection between the first excited state (S1) and the ground electronic state (S0), which emerges beyond the S1 minimum of 1E to the ring-closing side. The distinctive topography of this conical intersection appears to be sloped. These findings suggest a reduced quantum yield for the formation of the closed isomer, indicating a higher likelihood of reformation of the open isomer(s). The surface hopping simulation further supports this observation, revealing a mere ∼8% quantum yield for the formation of the closed isomer. In addition, the photoisomerization of the fulgide molecule initiates a cascade of conduction switching and holds great potential for applications in molecular electronics. Delving into the realm of molecular electronics, we have further examined the electron transport properties, disclosing the higher conductivity of the closed isomer. [ABSTRACT FROM AUTHOR]

The atmospheric oxidation of 1,1-dichloro-1,3,3,3-tetrafluoropropane, HCFC-234fb (DTP), leads to the formation of harmful radicals, contributing to stratospheric ozone depletion. Thus, a detailed study of the gas-phase oxidation of the first-generation chlorofluorocarbon alternative HCFC-234fb by a reaction with hydroxyl radicals and chlorine atoms is important to understand its harmful effects on the environment. In this work, we have performed quantum chemical calculations to investigate the thermodynamic and kinetic aspects of the titled reaction. The potential energy profile calculated at the CCSD(T)/aug-cc-pVTZ//MP2/cc-pVTZ level of theory shows that the major reaction pathway involves the abstraction of the H-atom from the central carbon atom, C2, giving rise to the product radical CF3C˙HCCl2F. The calculated rate-coefficients for the reaction with ˙OH and Cl-atoms are 3.89 × 10−15 and 2.54 × 10−17 cm3 molecule−1 s−1, respectively, at 298 K and are in accordance with the experimental rate coefficients. The results suggest that the rate-coefficient for the reaction of DTP with ˙OH is two orders of magnitude higher than that with Cl-atoms, indicating greater significance of the former reaction in the atmosphere. With the rate-coefficient values, the lifetime and the radiative efficiency were calculated to be 8.2 years and 0.246 W m−2 ppb−1, respectively. A 100-year global warming potential (GWP) of 712 was also estimated using the lifetime corrected radiative efficiency value. [ABSTRACT FROM AUTHOR]

In the ever-growing field of two-dimensional (2D) materials, the boron–sulfide (B2S2) monolayer is a promising new addition to MoS2-like 2D materials, with the boron (a lighter element) pair (B2 pair) having similar valence electrons to Mo. Herein, we have functionalized the h-phase boron sulfide monolayer by introducing oxygen atoms (Oh-B2S2) to widen its application scope as a gas sensor. The charge carrier mobilities of this system were found to be 790 × 102 cm2 V−1 s−1 and 32 × 102 cm2 V−1 s−1 for electrons and holes, respectively, which are much higher than the mobilities of the MoS2 monolayer. The potential application of the 2D Oh-B2S2 monolayer in the realm of gas sensing was evaluated using a combination of density functional theory (DFT), ab initio molecular dynamics (AIMD), and non-equilibrium Green's function (NEGF) based simulations. Our results imply that the Oh-B2S2 monolayer outperforms graphene and MoS2 in NO and NO2 selective sensing with higher adsorption energies (−0.56 and −0.16 eV) and charge transfer values (0.34 and 0.13e). Furthermore, the current–voltage characteristics show that the Oh-B2S2 monolayer may selectively detect NO and NO2 gases after bias 1.4 V, providing a greater possibility for the development of boron-based gas-sensing devices for future nanoelectronics. [ABSTRACT FROM AUTHOR]

We present an in-depth solution phase dynamics of rare seven coordinated pentagonal bipyramidal Mn(II) complexes, together with their binding affinity anticipated using ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT). Moreover, the simulations at different temperatures (25 °C and 90 °C) interpret the rigidity and stability of the ligands with Mn(II) ions. An intuitive approach for modulating the easy plane magnetic anisotropy of the mononuclear Mn(II) complex has been revealed by this work. In this regard, we have performed an extensive theoretical study based on the ab initio CASSCF/NEVPT2 method, exhibiting the presence of an easy plane magnetic anisotropy with a positive value of axial zero-field splitting (ZFS) parameter D. The complex's magnetic properties and electronic relaxation reveal that the rhombic ZFS term (E) can be modulated as the symmetry around the Mn(II) ion varies. The magnitude of the D-value increased with a more symmetrical equatorial ligand as found in the order of [Mn(pydpa)(H2O)] > [Mn(cbda)(H2O)]− > [Mn(dpaaa)(H2O)]− > [Mn(dpasam)(H2O)]−. Furthermore, we found that substituting the equatorial oxygen atom with heavier S and Se-donor atoms switches the sign of magnetic anisotropy for the Mn(II) complexes. The magnitude of the D-value increased when the energy levels of the ground state (GS) and the first excited state (ES) decreased. The observed magneto-structural correlation reveals that shortening the distance of the axial water molecule (Mn–O(w)) increases the D-value by an order of magnitude for the symmetrical [Mn(pydpa)(H2O)] complex. Overall, the combined analysis of solution phase dynamics of Mn(II) complexes and their magnetic characterization opens up new avenues in coordination chemistry, molecular magnetism, spin-crossover materials, and catalysis. [ABSTRACT FROM AUTHOR]

Single isolated molecules and supramolecular host–guest systems, which consist of π–π stacking interactions, are emerging as promising building blocks for creating molecular electronic devices. In this article, we have investigated the noncovalent π–π interaction and intermolecular electron charge transport involved in a series of host–guest complexes formed between a cage-like host (H6+) and polycyclic aromatic hydrocarbon (PAH) guests (G1–G7) using different quantum chemical approaches. The host (H6+) consists of two triscationic π-electron-deficient trispyridiniumtriazine (TPZ3+) units that are bridged face-to-face by three ethylene-triazole-ethylene. Our theoretical calculations show that the perylene and naphthalene inclusion complexes G7⊂H and G1⊂H have the highest and lowest interaction energies, respectively. In addition, energy decomposition analysis (EDA) indicated that the dispersion interaction term, ΔEdisp, significantly contributes to the host–guest interaction and is correlated with the existence of π–π van der Waals interaction. Using the nonequilibrium Greens function (NEGF) method in combination with density functional theory (DFT), the current–voltage (I–V) curves of the complexes were estimated. The conductance values increased when the guests were embedded inside the host cavity. Notably, the complex G7⊂H has the maximum conductance value. Overall, this study provided the electron transport of the PAH inclusion host–guest complex through π–π interaction and provided a direction for the fabrication of future supramolecular molecular devices. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopy in supersonic jet expansions is a powerful tool to assess molecular aggregates in close to ideal conditions for the benchmarking of quantum chemical approaches. The low temperatures achieved as well as the absence of environment effects allow for a direct comparison between computed and experimental spectra. This provides potential benchmarking data which can be revisited to hone different computational techniques, and it allows for the critical analysis of procedures under the setting of a blind challenge. In the latter case, the final result is unknown to modellers, providing an unbiased testing opportunity for quantum chemical models. In this work, we present the spectroscopic and computational results for the first HyDRA blind challenge. The latter deals with the prediction of water donor stretching vibrations in monohydrates of organic molecules. This edition features a test set of 10 systems. Experimental water donor OH vibrational wavenumbers for the vacuum-isolated monohydrates of formaldehyde, tetrahydrofuran, pyridine, tetrahydrothiophene, trifluoroethanol, methyl lactate, dimethylimidazolidinone, cyclooctanone, trifluoroacetophenone and 1-phenylcyclohexane-cis-1,2-diol are provided. The results of the challenge show promising predictive properties in both purely quantum mechanical approaches as well as regression and other machine learning strategies. [ABSTRACT FROM AUTHOR]

Interlayer charge transfer (CT) based on band alignment plays a vital role in various optoelectronic applications, such as photoluminescence modulation, superior photoconduction, etc. The layer-by-layer integration of atomically thin materials with different band alignments is an efficient approach to witness CT. To study interlayer CT, the stacking of ultrathin van der Waals (vdW) materials has been studied extensively, while the stacking of vdW materials with non-van der Waals (nvdW) materials is least explored. Herein, we present the stacking of an nvdW two-dimensional (2D) Bi2O2Se layer over a vdW 2D MoS2 (monolayer) and study the interlayer coupling and CT across the 2D interface. Studies through various spectroscopic and microscopic tools and density functional theory calculations reveal that significant interlayer CT occurs across the heterolayers due to the favorable band alignment of type-II across the junction. Interestingly, the CT from the 2D Bi2O2Se layer to the monolayer MoS2 results in photoluminescence (PL) quenching in the MoS2 layer and enhanced photoconduction in the HS. Low-temperature PL studies reveal that the robust interlayer coupling between the heterolayers enhances the CT process. The modified Varshni fit reveals that the electron–phonon coupling constant (Huang–Rhys factor) is higher for trions (1.13) than for neutral excitons (0.66) in the heterostructure. Upon photoexcitation, the trion–phonon coupling is stronger than the neutral exciton–phonon coupling in the heterostructure system. The additional doping caused by photogenerated CT was quantified by solving the coupled rate equations using a four-level model, and the results are fully consistent with the CT estimated from the density functional theory (DFT) calculation. These results are significant for understanding the interaction between vdW and nvdW 2D heterostructures and further exploration of such 2D heterostructures in future optoelectronic applications. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS), a very powerful tool for the identification of molecular species, has relied mostly on noble metal-based substrates to obtain a high enhancement factor. In this work, we demonstrate that self-driven intrinsic defects in 2D palladium di-selenide (PdSe2) dendrites grown at low temperature (280 °C) act as hotspots for high SERS enhancement. We grow 2D dendritic PdSe2 with ample intrinsic defects to exploit it for SERS application. X-ray electron spectroscopy (XPS) analysis reveals 9.3% outer layer and 4.7% interior Se vacancies. A detailed examination of atomic-scale defects revealed Se vacancy (VSe) coupled with Se–Pd–Se vacancy (VSe-Pd-Se) in monolayer PdSe2, and an array of line defects (Se vacancies) and nanopores in bilayer PdSe2 dendrites. Interestingly, our studies reveal that Se vacancy-rich PdSe2 gives rise to line defects that act like hotspots for SERS enhancement. Remarkably, the vacancy-rich dendritic PdSe2 shows a SERS enhancement factor >105 and can detect RhB at a concentration down to 10−8 M. We speculate that the topological line defects and the edge construction in PdSe2 dendrites act as metallic wire or edge, which is partly responsible for the high enhancement in the SERS signal. The high SERS sensitivity is explained on the basis of multiple charge transfer processes combined with the predicted metal-like behavior of the defected 2D PdSe2. Our conclusions are fully supported by the density functional theory calculation of the electronic density of states of the defective bilayer (2L) PdSe2, which remarkably exhibits metallic character. Being a defect-enabled SERS substrate, dendritic 2D PdSe2 fills the gap between conventional plasmonic SERS substrate and plasmon-free SERS substrate. [ABSTRACT FROM AUTHOR]

Three polycyclic chromeno[2,3-b]indolecontaining indole and naphthalene rings fused by a pyran ring were synthesized by metal-free C–H functionalization method and their photophysical studies were done. Steady state absorption spectra do not show solvent effect while fluorescence spectra exhibit solvatochromic shift. The molecules exhibit ultra-high Stokes shift of the order of 3.07 eV (24,696 cm−1) in acetonitrile and 2.12 eV (17,054 cm−1) in ethyl acetate. To corroborate experimental observation, we performed computational investigation both in gas and solvent phases. The computed results are in good agreement with the experimental observation. Analysis of the frontier molecular orbitals as well as natural transition orbitals depicts intramolecular charge transfer in the molecules. Further, gas phase as well as solvent phases optimized structures in the ground and excited states of all chosen molecules show increase in planarity in the excited state. An excited state intramolecular charge transfer accompanied by structural relaxation leading to planarity in the excited state has been suggested to cause large Stokes shifted fluorescence emission in these molecules. [ABSTRACT FROM AUTHOR]

Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2'-deoxycytidine-3'-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3' C-O bond cleavage from the lowest π * shape resonance in energy region < 1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the π * orbital of the base to the σ* orbital of the glycosidic N-C bond. In addition, the metastable state formed after impinging LEE (0-1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N-C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ~35-55 fs. Comparison of salient features of the two dissociation events, i.e., 3' C-O single strand break and glycosidic N-C bond cleavage in 3'-dCMPH molecule are also provided. [ABSTRACT FROM AUTHOR]

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2′-deoxycytidine-3′-monophosphate [3′-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π* to σ* resonance state which resembles a SN2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ5), which may have a substantial role during DNA damage. [ABSTRACT FROM AUTHOR]

Selective cleaving of both O–H and O–D bonds in HOD is achieved using reasonably simple UV pulses to excite the HOD molecule in its ground vibrational state to the repulsive first excited à (1B1) surface. Detailed theoretical analysis of population transfer and flux in theH+O–D/H–O+D channels reveals an important preparatory role for the cross-talk between the participating levels and a possible role for the beat structure of the population transfer oscillations in facilitating selective dissociation. Excitation using a 50 fs single color 67 169 cm-1 laserpulse achieves a branching ratio H+O–D/H–O+D=5.64 with 82% flux in theH+O–D channel and 15% in the H–O+D channel. A two color 50 fs laser pulse with frequencies of 54 920 and 52 303 cm-1 provides a branching ratio of H–O+D/H+O–D=2.83 and 52% flux in the H–O+D channel and 18% in the H+O–D channel. [ABSTRACT FROM AUTHOR]

Vibrational excitation (νf←νi) cross-sections σνf←νi(E) in resonant e-N2 and e-H2 scattering are calculated from transition matrix elements Tνf,νi(E) obtained using Fourier transform of the cross correlation function <[lowercase_phi_synonym]νf(R)|ψνi(R,t)>, where ψνi(R,t)≃e-iHA2-(R)t/h[lowercase_phi_synonym]νi(R) with time evolution under the influence of the resonance anionic Hamiltonian HA2-(A2-=N2-/H2-) implemented using Lanczos and fast Fourier transforms. The target (A2) vibrational eigenfunctions [lowercase_phi_synonym]νi(R) and [lowercase_phi_synonym]νf(R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curves of the neutral target. Application of this simple systematization to calculate vibrational structure in e-N2 and e-H2 scattering cross-sections provides mechanistic insights into features underlying presence/absence of structure in e-N2 and e-H2 scattering cross-sections. The results obtained with approximate PE curves are in reasonable agreement with experimental/calculated cross-section profiles, and cross correlation functions provide a simple demarcation between the boomerang and impulse models. [ABSTRACT FROM AUTHOR]

Quantum dynamical calculations are employed to study the significance of the photolysis frequency in enhancing the selectivity and yield for controlled bond breaking in HOD. The IR/UV pulse combinations are shown to provide extremely high selectivity and yield of the system.

Low energy electron (LEE) induced single strand break (SSB) has been studied for 2′-deoxycytidine-5′-monophosphate (5′-dCMPH) molecules in the gas phase by means of ab initio electronic structure methods and local complex potential based time-dependent wavepacket quantum mechanical calculations. We have found that the LEE attachment to this cytidine nucleotide results in the formation of a transient metastable anion. The results obtained here show that the electron attachment takes place at the cytosine nucleobase center and within 18–20 fs, the LEE transfers to the σ* orbital of the sugar-phosphate 5′ C–O bond. The characteristic electron attachment cross section spectrum is found at ∼1 eV, which is in good agreement with the available experimental observations. Quantum mechanical tunneling of the 5′ C–O bound vibrational energy levels may contribute to SSB only above 1.5 eV energy regimes. [ABSTRACT FROM AUTHOR]

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Quantum dynamical calculations on HOD subjected to different combinations of IR and UV pulses have been made to isolate field attributes which maximise selectivity and yield in the photodissociation of the desired O-H/O-D bond. Results from IR+UV pulse combinations which provide very high selectivity and/or yield are analysed in detail using population transfer, probability density flow, and flux variations to obtain microdynamic details favouring selectivity and yield. The expectation values for stretch and momentum in O-H and O-D bonds of the H-O-D molecule subjected to UV pulses effecting selective cleavage of these bonds have been analysed to decipher the mechanistic basis of selective dissociation. Fully quantum dynamical calculations using both the ground and excited potential energy surfaces with different initial states and UV pulses reveal that prior stretch in a bond before transferring it to the repulsive first excited state ensures preferential dissociation of this bond. The sampling of large stretch values and a quick downhill motion in the channel corresponding to dissociation of the prestretched bond on the upper surface are seen to underlie this preferential dissociation. [ABSTRACT FROM AUTHOR]

The structural features of vibrational excitation cross-sections in resonant e-H2 scattering have been investigated using a time dependent wave packet approach and a local complex potential to describe the 2Σu+ H2- anion. An analysis of the partial contributions to the vibrational excitation cross-sections reveals that all features of the excitation profile result from simple interference between bound vibrational levels of H2 and H2-. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Results from application of a new implementation of the time-dependent wave packet (TDWP) approach to the calculation of vibrational excitation cross-sections in resonant e-CO scattering are presented to examine its applicability in the treatment of e-molecule resonances. The results show that the SCF level local complex potential (LCP) in conjunction with the TDWP approach can reproduce experimental features quite satisfactorily. [ABSTRACT FROM AUTHOR]

Effect of quantum mechanical tunneling on single strand breaks induced by low energy electron (LEE) has been investigated in a modeled gas phase system, 2′-deoxycytidine-3′-monophosphate (3′-dCMPH). The potential energy curves for the sugar-phosphate C-O (3′ C-O) bond cleavage have been generated using second order Mo\ller-Plesset perturbation theory at the 6-31+G(d) accuracy level. Results from the electronic structure theory calculations in conjunction with our time dependent calculations for the 3′ C-O bond rupture in 3′-dCMPH using local complex potential based time dependent wave packet approach show significant quantum tunneling of the 3′ C-O bond from the bound vibrational states above 1 eV of the anionic potential energy curve. A comparison of the fragmentation profile with that of our earlier gas phase investigations based on Hartree-Fock and density functional theory - Becke, 3-parameter, Lee-Yang-Parr methods with 6-31+G(d) basis set is also provided. Further, inspection of the singly occupied molecular orbitals generated at different 3′ C-O bond lengths clearly indicates the electron transfer from the low lying base-π* shape resonance state to the phosphate P = O π* orbital of the DNA backbone during the strand breaks. The decisive step during LEE induced strand breaks follows via 'charge induced dissociation' (CID) for the metastable anion formed below 1 eV, whereas quantum mechanical tunnel-ing is out-weighted the CID mechanism for the LEE above 1 eV. [ABSTRACT FROM AUTHOR]

Exploring the electronic structure and dynamic behavior of Mn(II) complexes reveals fascinating magnetic properties and prospective biomedical applications. In this study, we investigate the solvent phase dynamics of heptacoordinated Mn(II) complexes through ab initio molecular dynamics simulations and density functional theory (DFT) calculations with effectively varying temperatures. We observed that the complex with high stability ([Mn(pmpa)(H 2 O) 2 ]) remains relatively rigid as the temperature increases to 90 °C, with only a minor change in its radial distribution functions (RDFs), compared to the RDF peaks at 25 °C. To elucidate the impact of halogens on the magnetic anisotropy of seven-coordinated Mn(II) complexes, we performed both DFT and multireference calculations. This shows that the zero-field splitting (ZFS) parameter D follows the order D (I)> D (Br)> D (Cl). We observed a significant increase in the D -value following the substitution of soft Se-donors in the equatorial position and heavier halogens in the axial position. The D -value of halogen derivatives of Se-analogues varies in the order of D (Cl) < D (I) < D (Br), deviating from the regular spectrochemical series with the discrepancy between the covalency of the Mn(II)-Se bond and the ligand field strength. We anticipate that this study will enhance our understanding of the solvent phase dynamics and structural aspects of ZFS in various Mn(II) complexes with different electronic environments.