Excited Electronic States Research Articles

Photodissociation of the CH2Cl radical: A high-level abinitio study.

Photodissociation of the CH2Cl radical is investigated by using high-level multireference configuration interaction abinitio methods, including the spin-orbit coupling. All possible fragmentation pathways, namely, CH2Cl + hν → CH2 + Cl, HCCl + H, and CCl + H2, have been analyzed. The potential-energy curves of the ground and several excited electronic states along the corresponding dissociating bond distance of each pathway have been calculated. Inclusion of the spin-orbit couplings is found to be crucial because it strongly determines the shape of the curves of the different excited states and, therefore, their photodissociation dynamics behavior. Analysis of the potential curves indicates that the pathways producing CH2 + Cl and HCCl + H can occur through a fast direct dissociation mechanism, while the pathway leading to CCl + H2 involves much slower dissociation mechanisms such as internal conversion between electronic states, predissociation, or tunneling through exit barriers. The main implications are that the two faster channels are predicted to be dominant, while the slower pathway is expected to be very unlikely and rather irrelevant. Appreciable actinic fluxes of solar irradiation are available at stratospheric altitudes where ozone is abundant, in the wavelength range where absorption of the first low-lying excited states of CH2Cl has been observed experimentally. Our results show that in this excitation energy range, the above-mentioned two dominant dissociation pathways are open and then could contribute to stratospheric ozone depletion.

Recent Advances in Understanding Triplet States in Metal Nanoclusters: Their Formation, Energy Transfer, and Applications in Photon Upconversion.

Recent experimental findings, rapidly accumulating over the past few years, has revealed that in the electronic excited states of metal nanoclusters (MNCs) composed of noble metal atoms (e.g., Cu, Ag, or Au), triplet states are generated with remarkably high efficiency, exerting a pivotal influence over the photophysical properties of the MNCs, notably their photoluminescence characteristics. As a result, MNCs are increasingly recognized as promising luminescent nanomaterials that exhibit room-temperature phosphorescence and thermally activated delayed fluorescence. Furthermore, the significance of triplet-state-mediated energy transfer and charge transfer in intermolecular photophysical processes is gaining increasing recognition, particularly in the applications of MNCs as photosensitizers for singlet oxygen and organic molecular triplets. This Perspective focuses on recent advances in understanding of the formation and photophysics of triplet states in MNCs. Additionally, a brief overview is provided of a series of studies exploring the use of MNCs as triplet sensitizers for photon upconversion via triplet-triplet annihilation, and future prospects for this emerging application are discussed.

Chiral Pd2L4 Capsules from Readily Accessible Tröger's Base Ligands Inducing Circular Dichroism on Fullerenes C60 and C70.

The induction of chirality on pristine fullerenes through non-covalent embedding in an asymmetric nano-confinement has only been rarely reported. Bringing molecules with such a unique electronic structure and broad application range into a chiral environment is particularly appealing for the development of chiroptical materials, enantioselective photoredox catalysts and systems showing chirality-induced spin selectivity (CISS). In this study, we report the formation of a chiral, configurationally stable Pd2L4capsule assembled from aC2-symmetric, 'ribbon-shaped' ligand with a Tröger's base naphthalimide (TbNaps) backbone, easily synthesized in three steps from commercially available compounds. Embedding chirality directly into the ligand backbone ensures a relatively lightweight receptor design whose aromatic panels create a strongly shielded inner cavity of about 700 Å3volume. Fullerenes C60and C70, as well as a pair of corannulenes, can be bound in acetonitrile (where unsubstituted fullerenes are insoluble) and X-ray structures of host-guest complexes were obtained. Tight interactions between the chiral host and the fullerene guests leads to the induction of a circular dichroism (CD) on the characteristic absorption bands of the forbidden π-π* transitions of the fullerenes, backed up by sTDA TD-DFT calculations and detailed investigation of the electronic excited states.

Anisotropic Dielectric Screened Range-Separated Hybrid Density Functional Theory Calculations of Charge Transfer States across an Anthracene-TCNQ Donor-Acceptor Interface.

A density functional theory framework is developed to study electronic excited states affected by an anisotropic dielectric environment. In particular, an anisotropic dielectric screened range-separated hybrid (SRSH[r]) functional is defined and combined with an anisotropic polarizable continuum model (PCM) implemented through a generalized Poisson equation solver. We develop the SRSH-PCM(r) approach and use it to quantify the effect of anisotropy on an excited charge transfer (CT) state energy. In particular, the dielectric interface effect on the CT state within a donor-acceptor molecular complex of antrancene and tetracyanoquinodimethane is studied. The donor-acceptor complex and the dielectric interface are used to represent the interface between thin films consisting of these materials. We report the effect of such a dielectric interface on the energy of a CT and follow its dependence on the donor-acceptor distance. We also benchmark the anisotropy-affected energy by comparing to homogeneous dielectric calculated energies. Due to the planar interface, the anisotropic energies are expected to to match with those obtained based on isotropic calculations of the larger dielectric constant at large enough distances. The approach is applicable, in general, to more complicated dielectric constant distributions as expected to be found in actual interfaces of such thin films or in other systems, for example, for CT processes within photosystems.

On the Ionization Tolerance of C20 Fullerene in Ground and Excited Electronic States in Planetary Nebulae

As the smallest member of the fullerene family, C20 is yet to be discovered in planetary nebulae. In this work, we present a quantum chemical study via density functional theory (DFT) and partially by the MP2 on the ionization tolerance of this molecule in the space environment. Considering that the ionization and excitation phenomena play key roles in demonstrating the lifetime of a molecule, we examined both ground and excited electronic-state potential energy surfaces (PES) of C20 and its cations C20q+. Our theoretical results indicate that the C20 cage tolerates a positive charge as high as 13+ by characterizing local minimum geometries on both the abovementioned electronic states. The results are backed by characterizing both C2012+ and C2013+ as local minimum geometries at the MP2 level of computations. We also explored, theoretically and systematically, scenarios in which the electronic structure of neutral C20 is excited to very high spin multiplicity (beyond triplet state), and local minimum molecular geometries with cage structures are well characterized. We anticipate that such structural resistance to excitation and ionization delivers a prolonged lifetime necessary for the spectroscopic detection of this interesting molecule and its cations in space and potentially in planetary nebulae (PN).

Comment on “Relativistic spinless energies and thermodynamic properties of sodium dimer molecule”

In this Comment we point out two incorrect results in a paper published recently in this journal. In the first place, the fact that the maximum number of vibrational energy levels is not a variable parameter of the model because it is determined by the potential-energy function and, in particular, by the dissociation energy. In the second place, we argue that the vibrational thermodynamic functions for an excited electronic state of a diatomic molecule are of no physical utility because any physical application requires the more relevant contribution of the lower electronic states to the canonical partition function. To illustrate this point we show the calculation of the equilibrium constant for the dimerization of sodium using only spectroscopic information about the ground electronic state. The theoretical expression agrees remarkably well with the available experimental data.

Ultrafast Mapping of Electronic and Nuclear Structure in the Photo Dissociation of Nitrogen Dioxide.

We investigate the photoinduced dissociation reaction of NO2 → NO + O upon electronic excitation of the X̃2A1 (D0) to the Ã2B2 (D1) state by femtosecond X-ray absorption spectroscopy at the nitrogen K-edge. We obtain key insight into the chemical bond breaking event and its associated electronic structural dynamics. Calculations of the photoinduced reaction allow to assign the transient absorption features at time scales of 10-50 fs to wave packet motions in the excited D1 and ground D0 states, followed by the formation of the NO photoproduct with a 255 ± 23 fs time constant. Our analysis shows that there is no direct correlation between the 1s core levels and the electronic ground and excited states transition energies and the bond elongation of NO2, while en route to dissociation toward the NO + O photoproducts, in the transient nitrogen K-edge spectra. However, simulations predict that for a sufficiently short UV pump pulse, the early wave packet dynamics in the D1 electronic excited state occurring within the first 35 fs along the bending and symmetric stretching modes can be directly mapped in the transient X-ray absorption spectra.

Spectroscopic signatures of the S0, S1, and D0 states of indan: An experimental and theoretical investigation

The electronic and vibrational spectra of indan were explored through the utilization of Fourier transform infrared (FT-IR) spectrum, one-color resonant two-photon ionization (1C-R2PI) spectrum, and two-color resonant two-photon ionization (2C-R2PI) slow electron velocity-map imaging (SEVI) techniques in combination with quantum chemical calculations. Experimental spectra are found to be in good overall accordance with the theoretical calculations. The vibrational modes of the S0 neutral ground state, S1 first electronic excited state, and D0 cationic ground state were assigned with the assistance of density functional theory (DFT) calculations. The S1 ← S0 electronic transition energy was determined to be 36909 ± 5 cm−1 from the one-color resonant two-photon ionization spectrum. Moreover, the adiabatic ionization energy was deduced as 68419 ± 6 cm−1 based on the SEVI spectra.

Measurements of the Rovibrationally Dependent Lifetimes of C2 in the 13Σg+ and f3Σg- States through the VUV-Pump-UV-Probe Scheme.

The dicarbon molecule, C2, is one of the most important diatomic species in various gaseous environments. Despite extensive spectroscopic studies in the last two centuries, the radiative and photodissociative properties of C2 in its highly excited electronic states are still largely unexplored, particularly in the short vacuum ultraviolet (VUV) region. In this study, the lifetimes of C2 for rotational levels in the recently identified 13Σg+ state up to the vibrational level ν' = 4 and in the f3Σg- state up to ν' = 2 are measured for the first time with a VUV-pump-UV-probe photoionization scheme. It is found that all rovibrational levels in the f3Σg- state have lifetimes shorter than the dynamical limit of ∼4.7 ns of the present method, and the lifetimes in the 13Σg+ state show obvious and complex dependence on the rotational and vibrational quantum levels. Generally, the lifetime in the 13Σg+ state becomes shorter at higher rotational and vibrational levels, i.e., the longest lifetime measured in the ν' = 0 level is ∼18 ns, while all rotational levels in the ν' = 4 level are found to have shorter lifetimes than ∼4.7 ns. This implies that predissociation might occur and become more prominent at the higher energy levels in the 13Σg+ state. The prominent dependence of the lifetime on the rotational, vibrational and electronic level indicates complex dynamical processes in the highly excited states of C2.

Anion Photoelectron Spectroscopy and Ab Initio Studies of the UF- Anion.

A synergistic anion photoelectron spectroscopic and ab initio computational study of photodetachment of UF- is reported. The measurement determined a vertical detachment energy of 0.63(03) eV, which is consistent with a spinor-based relativistic coupled-cluster CCSD(T) value of 0.61 eV. The complex spectral features due to excited electronic states and vibrational progressions of UF are analyzed and assigned with the help of spin-orbit-coupled multireference perturbation theory and spinor-based relativistic coupled-cluster calculations. UF and UF- are confirmed to be dominated by ionic bonding. The usefulness of the spinor CCSD(T) approach is demonstrated.

Helical-photon-dressed states determining unidirectional π-electron rotations in aromatic ring molecules.

We theoretically demonstrated that helical-photon-dressed states determine the rotational directions of the π-electrons of aromatic ring molecules formed by a circularly polarized or an elliptically polarized laser. This theory was verified using a minimal three-electronic-state model under the frozen nuclei condition. The model consists of the ground state and either a doubly degenerate electronic excited state or two quasi-degenerate excited states. Three helical-photon-dressed states were derived by solving the time-dependent Schrödinger equation within the semi-classical treatment of light-molecule interactions and rotating wave approximation. The angular momenta of the two helical-photon-dressed states represent the classical rotational direction, and that of the remaining state represents the opposite rotation, that is, non-classical rotation. Classical rotation means that π-electrons have the same rotational direction as that of a given helical electric field vector and obeys the classical equations of motion. Non-classical rotation indicates that the rotational direction is opposite to that of the helical electric field vector. Non-classical rotation is forbidden in an aromatic ring molecule with high symmetry formed by a circularly polarized laser but is allowed in a low symmetric aromatic ring molecule. The sum of the angular momenta of the three dressed states is zero. This is called the sum law for the angular momentum components in this paper. Benzene (D6h) and toluene (CS) were adopted as typical aromatic ring molecules of high and low symmetries, respectively. Finally, considering the effects of nuclear vibrations in the adiabatic approximation, an expression for the π-electron angular momentum was derived and applied to toluene.

Different Photodissociation Mechanisms in Fe(CO)5 and Cr(CO)6 Evidenced with Femtosecond Valence Photoelectron Spectroscopy and Excited-State Molecular Dynamics Simulations.

Measured and calculated time-resolved photoelectron spectra and excited-state molecular dynamics simulations of photoexcited gas-phase molecules Fe(CO)5 and Cr(CO)6 are presented. Samples were excited with 266 nm pump pulses and probed with 23 eV photons from a femtosecond high-order harmonic generation source. Photoelectron intensities are seen to blue-shift as a function of time from binding energies characteristic of bound electronic excited states via dissociated-state energies toward the energies of the dissociated species for both Fe(CO)5 and Cr(CO)6, but differences are apparent. The excited-state and dissociation dynamics are found to be faster in Cr(CO)6 because the repopulation from bound excited to dissociative excited states is faster. This may be due to stronger coupling between bound and dissociative states in Cr(CO)6, a notion supported by the observation that the manifolds of bound and dissociative states overlap in a narrow energy range in this system.

Importance of Electron Correlation on the Geometry and Electronic Structure of [2Fe-2S] Systems: A Benchmark Study of the [Fe2S2(SCH3)4]2-,3-,4-, [Fe2S2(SCys)4]2-, [Fe2S2(S-p-tol)4]2-, and [Fe2S2(S-o-xyl)4]2- Complexes.

Iron-sulfur clusters are crucial for biological electron transport and catalysis. Obtaining accurate geometries, energetics, manifolds of their excited electronic states, and reduction energies is important to understand their role in these processes. Using a [2Fe-2S] model complex with FeII and FeIII oxidation states, which leads to different charges, i.e., [Fe2S2(SMe)4]2-,3-,4-, we benchmarked a variety of computational methodologies ranging from density functional theory (DFT) to post-Hartree-Fock methods, including complete active space self-consistent field (CASSCF), multireference configuration interaction, the second-order N-electron valence state perturbation theory (NEVPT2), and the linearized integrand approximation of adiabatic connection (AC0) approaches. Additionally, we studied three experimentally well-characterized complexes, [Fe2S2(SCys)4]2-, [Fe2S2(S-o-tol)4]2-, and [Fe2S2(S-o-xyl)4]2-, via DFT methods. We conclude that the dynamic electron correlation is important for accurately predicting the geometry of these complexes. Broken symmetry (BS) DFT correctly predicts experimental geometries of low-spin multiplicity, while CASSCF does not. However, BS-DFT significantly overestimates the difference between the low- and high-spin electronic states for a given oxidation state. At the same time, CASSCF underestimates it but provides relative energies closer to the reference NEVPT2 results. Finally, AC0 provides energetics of NEVPT2 quality with the additional advantage of being able to use large CASSCF sizes. NEVPT2 gives the best estimates of the FeIII/FeIII → FeII/FeIII (4.27 eV) and FeII/FIII → FeII/FII (7.72 eV) reduction energies. The results provide insight into the electronic structure of these complexes and assist in the understanding of their physical properties.

Efficient Photocatalytic Hydrogen Production Using In-Situ Polymerized Gold Nanocluster Assemblies.

Gold nanoparticles (NPs) are widely recognized as co-catalysts in semiconductor photocatalysis for enhancing hydrogen production efficiency, but they are often overlooked as primary catalysts due to the rapid recombination of excited-state electrons. This study presents an innovative gold-based photocatalyst design utilizing an in situ dopamine polymerization-guided assembly approach for efficient H2 generation via water splitting. By employing gold superclusters (AuSCs; ≈100nm) instead of ultra-small gold nanoclusters (AuNCs; ≈2nm) before polymerization, unique nanodisk-like 3D superstructures consisting of agglomerated 2D polydopamine (PDA) nanosheets with a high percentage of uniformly embedded AuNCs are created that exhibit enhanced metallic character post-polymerization. The thin PDA layer between adjacent AuNCs functions as an efficient electron transport medium, directing excited-state electrons toward the surface and minimizing recombination. Notably, the AuSCs@PDA structure shows the largest potential difference (26.0mV) compared to AuSCs (≈18.4mV) and PDA NPs (≈14.6mV), indicating a higher population of accumulated photo-generated carriers. As a result, AuSCs@PDA achieves a higher photocurrent density, improved photostability, and lower charge transfer resistance than PDA NPs, AuSCs, or AuNCs@PDA, with the highest hydrogen evolution rate of 3.20mmol g-1h-1. This work highlights a promising in situ polymerization strategy for enhancing photocatalytic hydrogen generation with metal nanoclusters.

Acoustic cavitation assisted synthesis of PCDs@PVA composite film for UV shielding, intelligent pH detection, information encryption and food packing applications

Excessive exposure to UV and high-energy blue light (HEBL) can severely damage the skin and eyes. Therefore, it is essential to protect our bodies from UV and HEBL radiation. We created PEG-derived carbon dots (PCDs) using the acoustic cavitation approach in order to completely block UV and HEBL. The influence of different experimental parameters such as sonication time, amplitude, and temperature on the PCDs is examined. The optimized PCDs are found to have an average diameter ranging from 5 to 9 nm, contingent upon the preparation circumstances, and to have a quantum yield (QY) of 14–16 %. The PCDs vivid colour and simultaneous UV and HEBL absorption properties allowed the PVA film containing 0.120 wt% of PCDs to demonstrate outstanding blocking efficiency, with 99.9 % blocking in HEBL and 100 % blocking in UV-C, UV-B, and UV-A. The photoluminescence (PL) behaviour of PCDs is greatly reduced by Fe3+ ions because of strong excited state electron transfer. This fluorescent “turn-off” behaviour towards Fe3+ is highly selective and sensitive with a limit of detection (LoD) of 0.366 μM. Paper-based sensors incorporating PCDs are developed for the rapid and accurate detection of Fe3+ in surface water, wastewater treatment plant effluent, and tap water, leveraging their excellent sensitivity and selectivity towards Fe3+. The characteristics of ink-free patterned substrates are displayed by PCDs scattered across a PVA matrix, which makes them useful for the non-destructive acquisition and recognition of latent fingerprints (LFPs). A flexible, transparent film is produced when a LFP is exposed to a PCDs@PVA solution. In this film, a steady luminous fingerprint with specific ridge characteristics that aid in personal recognition is seen. This method shows promise for lifting and identifying long-exposed LFPs from various surfaces without causing damage. It is believed that the interfacial segregation of PCDs inside the PVA matrix during the film production process serves as a mechanism for LFP collection and visualization. The YOLOv8x program, which utilizes deep convolutional neural networks, is employed to analyze the discernible features present in fingerprints (FPs). Notably, their exceptional flexibility, foldability, and sustainability create new opportunities for use in the anti-counterfeiting (AC) field. Because of its remarkable fluorescence stability, it may be a viable substitute for conventional fluorescent inks. Fresh green apples are observed over time after being coated with 0.120 wt% PCDs@PVA and PVA. Virtual assessments indicated that the 0.120 wt% PCDs@PVA film coating significantly reduced weight and moisture loss, effectively inhibiting fungal growth and spoilage for over 25 days at room temperature (RT). Overall, the results clearly show that the PCDs@PVA film is easy to make, flexible, safe for the environment, and resistant to photodegradation. Hemolysis, and blood clotting exhibited favorable biocompatibility and nontoxicity.

On the valence shell spectroscopy of 1,2-dichlorobenzene

We report high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of 1,2-dichlorobenzene in the photon energy range 4.0–10.8 eV (310–115 nm). The electronic state spectroscopy of ortho-C6H4Cl2 has been investigated together with quantum chemical calculations at different levels of theory, also providing vertical excitation energies and oscillator strengths. The valence, mixed valence-Rydberg and Rydberg character of the electronic transitions is accompanied by fine structure which has been mainly assigned to in-plane breathing with C–Cl stretching, v7′a1, ring breathing and C–C stretching, v8′a1, in-plane ring breathing, v9′a1, C–Cl symmetric stretching, v10′a1, and in-plane C–Cl bending v11′a1 modes. The experimental absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of 1,2-dichlorobenzene in the Earth’s atmosphere (0–50 km), showing that solar photolysis is expected to be a weak sink at altitudes lower than 20 km relative to OH radical reactions. Potential energy curves for the lowest-lying excited electronic states, as a function of the C–Cl stretching and in-plane C–Cl bending coordinates, were also obtained employing the time dependent density functional theory (TD-DFT) method. The results show the importance of the complex quasi-degenerate nature of the lowest-lying electronic states which in the intricate nuclear dynamics of the reaction coordinates, yield relevant internal conversion from Rydberg to valence character and in the asymptotic limit bond excision.

Unusual Hydrophobic Property of Blue Fluorescent Amino Acid 4-Cyanotryptophan.

It is a common belief that the negative heat capacity change (ΔCp) associated with protein folding, which is a manifestation of the hydrophobic effect, results from a decrease in the solvent accessible hydrophobic surface area. Herein, we investigate the conformational energy landscape and dynamics of a tetrapeptide composed of two glycine and two 4-cyanotryptophan residues using time-resolved fluorescence spectroscopy, molecular dynamics simulations, and density functional theory calculations and find that, contrary to this expectation, the hydrophobic association of two 4-cyanotryptophan side chains leads to a positive ΔCp (approximately 543 J K-1 mol-1). Furthermore, we find that promoting one of the 4-cyanotryptophans to its excited electronic state strengthens this self-association. Taken together, our results provide not only insight into how modification of an aromatic amino acid can affect its hydrophobicity but also a potential strategy for designing protein sequences that can fold (unfold) at high (low) temperatures.

Proteolysis-regulated excited state electron transfer of Ag2S/In(OH)3@BSA nanocomposites for fluorescence-photoelectrochemistry dual-mode biosensing of heparin

Sharing the same photoexcitation process, fluorescence (FL) and photoelectrochemistry (PEC) accomplish optical-optical and optical-electrochemical switches respectively, and are both widely used in diverse fields. However, since FL and PEC are mutually exclusive in principle, it is difficult to obtain intense FL and PEC responses in a system, limiting FL-PEC dual-mode applications. In this study, Ag2S quantum dots (QDs) and In(OH)3 nanoblocks (NBs) are simultaneously synthesized by BSA-templated bio-mineralization, and the excited state electrons of Ag2S/In(OH)3@BSA nanocomposites (NCs) are further regulated by a proteolysis process. Owing to the coating of BSA, excited state electrons primarily return to ground state via radiation transition, resulting in a robust FL signal. When BSA is hydrolyzed by trypsin, the excited state electrons preferentially transfer to the electron acceptors, and the exposed Ag2S/In(OH)3@BSA NCs generate a strong PEC signal. Consequently, heparin, acting as an inhibitor of trypsin, can regulate the FL-PEC switch, allowing for the quantification of heparin by both the decrease in FL signals and the increase in PEC signals. Therefore, a dual-mode biosensor is established to detect heparin using FL and PEC signals, with linear ranges of 0.75–750 U mL−1 and 3.75 × 10−3 to 37.5 U mL−1, and limits of detection of 0.68 U mL−1 and 4.97 × 10−4 U mL−1, respectively. Additionally, the biosensor is used to monitor the rapid metabolism of heparin within 20 h in rats. Overall, this work demonstrates that manipulating excited state electrons of nanomaterials through a biological process offers an alternative perspective for designing FL-PEC dual-mode sensing systems.

Probing the Electronic Manifold of MgCl with Millimeter-Wave Spectroscopy and Theory: (3)2Σ+ and (4)2Σ+ States.

The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been observed in two new electronic excited states, (3)2Σ+ and (4)2Σ+, using direct absorption methods. The molecule was synthesized in a mixture of Cl2, argon, and magnesium vapor. For the (3)2Σ+ state, multiple rotational transitions were measured in the v = 0 level for all six isotopologues (24Mg35Cl, 24Mg37Cl, 25Mg35Cl, 25Mg37Cl, 26Mg35Cl, and 26Mg37Cl), as well as up to v = 13 for 24Mg35Cl. For the (4)2Σ+ state, less intense spectra were recorded for 24Mg35Cl (v = 0-2). Equilibrium rotational parameters were determined for both states for 24Mg35Cl, as well as rotational constants and 25Mg hyperfine parameters for the other isotopologues. A perturbation was observed between rotational levels of the two states due to an avoided crossing. Computations were also carried out at the CASPT2 and MRCISD+Q levels, and the resulting bond lengths for (3)2Σ+ and (4)2Σ+ states agree well with the experimental values of re = 2.536 and 2.361 Å. The computations show that the (3)2Σ+ state has a double-well potential; however, the state behaves as a single well with unperturbed vibrational levels up to v = 13 due to nonadiabatic interactions with the (4)2Σ+ state.

Nonadiabatic Excited-State Molecular Dynamics with an Explicit Solvent: NEXMD-SANDER Implementation.

In this article, the nonadiabatic excited-state Molecular dynamics (NEXMD) package is linked with the SANDER package, provided by AMBERTOOLS. The combination of these software packages enables the simulation of photoinduced dynamics of large multichromophoric conjugated molecules involving several coupled electronic excited states embedded in an explicit solvent by using the quantum/mechanics/molecular mechanics (QM/MM) methodology. The fewest switches surface hopping algorithm, as implemented in NEXMD, is used to account for quantum transitions among the adiabatic excited-state simulations of the photoexcitation and subsequent nonadiabatic electronic transitions, and vibrational energy relaxation of a substituted polyphenylenevinylene oligomer (PPV3-NO2) in vacuum and methanol as an explicit solvent has been used as a test case. The impact of including specific solvent molecules in the QM region is also analyzed. Our NEXMD-SANDER QM/MM implementation provides a useful computational tool to simulate qualitatively solvent-dependent effects, like electron transfer, stabilization of charge-separated excited states, and the role of solvent reorganization in the molecular optical properties, observed in solution-based spectroscopic experiments.