Naphthalene Dimer Research Articles

Improving second-order Møller-Plesset perturbation theory for noncovalent interactions with the machine learning-corrected abinitio dispersion potential.

In this work, we utilize our recently developed machine learning (ML)-corrected abinitio dispersion (aiD) potential, known as D3-ML, which is based on the comprehensive SAPT10K dataset and relies solely on Cartesian coordinates as input, to address the dispersion deficiencies in second-order Møller-Plesset perturbation theory (MP2) by replacing its problematic dispersion and exchange-dispersion terms with D3-ML. This leads to the development of a new dispersion-corrected MP2 method, MP2+aiD(CCD), which outperforms other spin-component-scaled and dispersion-corrected MP2 methods as well as popular ML models for predicting noncovalent interactions across various datasets, including S66 × 8, NAP6 (containing 6 naphthalene dimers), L7, S12L, DNA-ellipticine, the C60 dimer, and C60[6]CPPA. In addition, MP2+aiD(CCD) exhibits comparable or even superior performance compared to the contemporary ωB97M-V functional. The limited performance of pure ML models for systems outside the training set or larger than those in the training set highlights their instability and unpredictability. Conversely, the outstanding performance and transferability of the hybrid MP2+aiD(CCD) method can be attributed to the fusion of the physical electronic structure method and a data-driven ML model, combining the strengths of both sides. This investigation firmly establishes MP2+aiD(CCD) as one of the most accurate and reliable fifth-order scaling correlated wave function methods currently available for modeling noncovalent interactions, even for large complexes. MP2+aiD(CCD) is expected to be reliably applicable in investigating real-life complexes at the hundred-atom scale.

Near-infrared absorption and radiative cooling of naphthalene dimers (C10H8)2.

The radiative cooling of naphthalene dimer cations, (C10H8)2+ was studied experimentally through action spectroscopy using two different electrostatic ion-beam storage rings, DESIREE in Stockholm and Mini-Ring in Lyon. The spectral characteristics of the charge resonance (CR) band were observed to vary significantly with a storage time of up to 30 seconds in DESIREE. In particular, the position of the CR band shifts to the blue, with specific times (inverse of rates) of 0.64 s and 8.0 s in the 0-5 s and 5-30 s storage time ranges, respectively. These long-time scales indicate that the internal energy distribution of the stored ions evolves by vibrational radiative cooling, which is consistent with the absence of fast radiative cooling via recurrent fluorescence for (C10H8)2+. Density functional based tight binding calculations with local excitations and configuration interactions (DFTB-EXCI) were used to simulate the absorption spectrum for ion temperatures between 10 and 500 K. The evolution of the bandwidth and position with temperature is in qualitative agreement with the experimental findings. Furthermore, these calculations yielded linear temperature dependencies for both the shift and the broadening. Combining the relationship between the CR band position and the ion temperature with the results of the statistical model, we demonstrate that the observed blue shift can be used to determine the radiative cooling rate of (C10H8)2+.

Modulating molecular plasmons in naphthalene via intermolecular interactions and strong light-matter coupling.

We conducted a theoretical investigation on the modulation of plasmon-like resonances in naphthalene - the so-called molecular plasmons - through intermolecular interactions and strong light-matter coupling. The configuration interaction with single excitations (CIS) approach and its quantum electrodynamics extension (QED-CIS-1) are used to describe the molecular plasmon states under these interactions. We detail the effects of changing intermolecular distances of the naphthalene dimer and incorporating the naphthalene molecule into optical cavities, both allowing for precise control of naphthalene's plasmonic responses. Our results show significant shifts of the plasmon peak in the absorption spectra of naphthalene, depending on the spatial configuration of the dimer and cavity parameters such as polarization, frequency, and coupling strength. Further investigation of the naphthalene dimer in a cavity reveals a synergistic effect on the plasmon peak when the two types of interactions are combined. This research provides insights into the plasmonic behavior of simple polyacenes like naphthalene and opens up possibilities for plasmon modulation in more complex systems.

Machine-learned dynamic disorder of electron transfer coupling.

Electron transfer (ET) is a fundamental process in chemistry and biochemistry, and electronic coupling is an important determinant of the rate of ET. However, the electronic coupling is sensitive to many nuclear degrees of freedom, particularly those involved in intermolecular movements, making its characterization challenging. As a result, dynamic disorder in electron transfer coupling has rarely been investigated, hindering our understanding of charge transport dynamics in complex chemical and biological systems. In this work, we employed molecular dynamic simulations and machine-learning models to study dynamic disorder in the coupling of hole transfer between neighboring ethylene and naphthalene dimer. Our results reveal that low-frequency modes dominate these dynamics, resulting primarily from intermolecular movements such as rotation and translation. Interestingly, we observed an increasing contribution of translational motion as temperature increased. Moreover, we found that coupling is sub-Ohmic in its spectral density character, with cut-off frequencies in the range of 102 cm-1. Machine-learning models allow direct study of dynamics of electronic coupling in charge transport with sufficient ensemble trajectories, providing further new insights into charge transporting dynamics.

π-Stacking Isomerism in Polycyclic Aromatic Hydrocarbons: The 2-Naphthalenethiol Dimer.

π-Stacking is a common descriptor for face-to-face attractive forces between aromatic hydrocarbons. However, the physical origin of this interaction remains debatable. Here we examined π-stacking in a model homodimer formed by two thiol-substituted naphthalene rings. Two isomers of the 2-naphthalenethiol dimer were discovered using rotational spectroscopy, sharing a parallel-displaced crossed orientation and absence of thiol-thiol hydrogen bonds. One of the isomers presents C2 symmetry, structurally analogous to the global minimum of the naphthalene dimer. The experimental data were rationalized with molecular orbital calculations, revealing a shallow potential energy surface. Noncovalent interactions are dominated by dispersion forces according to SAPT energy decomposition. In addition, the reduced electronic density shows a diffuse and extended region of inter-ring interactions, compatible with the description of π-stacking as a competition between dispersion and Pauli repulsion forces.

Intermolecular Interactions and Charge Resonance Contributions to Triplet and Singlet Exciton States of Oligoacene Aggregates

Intermolecular interactions modulate the electro-optical properties of molecular materials and the nature of low-lying exciton states. Molecular materials composed by oligoacenes are extensively investigated for their semiconducting and optoelectronic properties. Here, we analyze the exciton states derived from time-dependent density functional theory (TDDFT) calculations for two oligoacene model aggregates: naphthalene and anthracene dimers. To unravel the role of inter-molecular interactions, a set of diabatic states is selected, chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space including two occupied and two unoccupied orbitals for each molecular monomer. We study energy profiles and disentangle inter-state couplings to disclose the (CT) character of singlet and triplet exciton states and assess the influence of inter-molecular orientation by displacing one molecule with respect to the other along the longitudinal translation coordinate. The analysis shows that (CT) contributions are relevant, although comparably less effective for triplet excitons, and induce a non-negligible mixed character to the low-lying exciton states for eclipsed monomers and for small translational displacements. Such (CT) contributions govern the La/Lb state inversion occurring for the low-lying singlet exciton states of naphthalene dimer and contribute to the switch from H- to J-aggregate type of the strongly allowed Bb transition of both oligoacene aggregates.

Cover Feature: Triplet‐triplet Annihilation Dynamics of Naphthalene (Chem. Eur. J. 40/2022)

Triplet–triplet annihilation (TTA)-based photon upconversion involves the fusion of two non-emissive triplet excited states into one singlet excited state. The TTA process in naphthalene is found to be mediated by conical intersection between the T1T1 and S1S0 states. The coupling of an optical cavity to a naphthalene dimer results in an increase in the efficiency of TTA-assisted photon upconversion process. More information can be found in the Research Article by M. Gudem and M. Kowalewski (DOI: 10.1002/chem.202200781).

State-specific solvation for restricted active space spin-flip (RAS-SF) wave functions based on the polarizable continuum formalism.

The restricted active space spin-flip (RAS-SF) formalism is a particular form of single-reference configuration interaction that can describe some forms of strong correlation at a relatively low cost and which has recently been formulated for the description of charge-transfer excited states. Here, we introduce both equilibrium and nonequilibrium versions of a state-specific solvation correction for vertical transition energies computed using RAS-SF wave functions, based on the framework of a polarizable continuum model (PCM). Ground-state polarization is described using the solvent's static dielectric constant and in the nonequilibrium solvation approach that polarization is modified upon vertical excitation using the solvent's optical dielectric constant. Benchmark calculations are reported for well-studied models of photo-induced charge transfer, including naphthalene dimer, C2H4⋯C2F4, pentacene dimer, and perylene diimide (PDI) dimer, several of which are important in organic photovoltaic applications. For the PDI dimer, we demonstrate that the charge-transfer character of the excited states is enhanced in the presence of a low-dielectric medium (static dielectric constant ɛ0 = 3) as compared to a gas-phase calculation (ɛ0 = 1). This stabilizes mechanistic traps for singlet fission and helps to explain experimental singlet fission rates. We also examine the effects of nonequilibrium solvation on charge-separated states in an intramolecular singlet fission chromophore, where we demonstrate that the energetic ordering of the states changes as a function of solvent polarity. The RAS-SF + PCM methodology that is reported here provides a framework to study charge-separated states in solution and in photovoltaic materials.

Surface Reactivity of Carbonaceous Nanoparticles: The Importance of Surface Pocket

The surface reactivity of carbonaceous nanoparticles is revealed from the barrier height and reaction enthalpy of hydrogen abstraction reaction by H radicals computed at the M06-2X/6–311g(d,p)//B3LYP/6-311G(d,p) level of theory. Small polycyclic aromatic hydrocarbon (PAH) clusters are selected as the model system of carbonaceous nanoparticles. The PAHs considered are naphthalene, pyrene, coronene, ovalene and circumcoronene. Cluster sizes range from dimer to tetramer with a parallel or crossed configuration. All results show similar values as that of monomers, but naphthalene dimers with a crossed configuration yield a lower barrier height and reaction enthalpy by ∼2 kcal/mol. A minor size dependence is noticed in the series of naphthalene clusters where a larger cluster exhibits a smaller barrier height. Larger homogeneous PAH clusters in a size range of 1.1–1.9 nm are later generated to mimic nascent soot surface. It is found that the barrier height decreases with the increase in particle size, and the averaged values are ∼2 kcal/mol lower than that of monomers. More importantly, a larger particle shows a wider spread in barrier heights, and low barrier heights are seen in the surface shallow regions (e.g., surface pockets). The lowest barrier height of ∼8.5 kcal/mol is observed at a C-H site locating in a surface pocket. A set of model systems are built to reveal the underlying mechanism of reduction in barrier height. It is shown that the reduction is caused by local interactions between the neighboring atoms and the local curvature. Further analysis on the average localized ionization potential shows that larger particles have higher reactivity, further supporting our findings from the barrier height of hydrogen abstraction reactions. Therefore, it is concluded that the surface reactivity depends on the particle size and the most reactive sites always locate at the surface pockets.

(Invited) Ultrafast Excited State Dynamics of Twisted Aromatics

Self-assembling of organic chromophoric systems into elegant supramolecular architectures with emergent properties has received prodigious attention in recent years.1 The notion of ‘emergence upon assembly’ is evidenced in the unusual photoexcited state dynamics exhibited by chromophoric assemblies. In the first example, a naphthalene-naphthalimide donor-acceptor (D-A) dyad assembled into segregated D-A stacks in the crystalline state. The photo-induced charge separated state in the aggregate state lasts 10,000 times longer than the monomeric dyad. The femtosecond transient absorption spectra depicted the spectroscopic signature for naphthalene dimer radical cation indicating the migration of charges through the stacks.2 In the second example, we report the crystalline evidence for Greek cross‐dipole (α=90°) stacking of 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxylic tetrabutylester (PTE‐Br2) displaying null excitonic coupling and thereby monomeric optical behavior. Additionally, the semi‐classical Marcus theory of charge‐transfer rates predicted a selective hole transport phenomenon in the orthogonally stacked PTE‐Br2.3 In the third example, we showcase a radial assembly of 1,8-dibromonaphthalene(2,6-diisopropylphenyl)imide (NIBr2) in crystalline phase driven by hexabromine synthon.4 NIBr2 exhibits ultrafast intersystem crossing5 and solid-state room temperature phosphorescence. We believe the fundamental understanding of noncovalent interactions dictating the unorthodox assembly of chromophores6-7 and probing of emergent properties are paramount for the rational design and construction of robust functional materials.8-9

High-resolution infrared spectroscopy of naphthalene and acenaphthene dimers

Non-covalent interactions are rapidly gaining interest as they are often crucial in determining the properties of materials, and key to supramolecular chemistry and to biochemistry. Non-covalent Polycyclic Aromatic Hydrocarbon (PAH) complexes are in particular relevant to astrochemistry and combustion chemistry where they are involved in the initial steps of condensation and soot formation, respectively. Here, we investigated non-covalent π-π stacking and CH-π interactions in naphthalene and acenaphthene clusters using high-resolution IR-UV spectroscopy in combination with quantum chemical calculations. We identified spectral shifts that occur upon complexation and thereby evaluated predicted potential energy surfaces. Although theory predicts a blueshift, a redshift is observed for the aliphatic CH-π interactions in the experimental spectrum of acenaphthene upon dimerization, indicating that CH-π interaction indeed affects the aliphatic bonds, while a blueshift is predicted, consequently theory deserves attention here. The results provide strong indications for a prevalent parallel naphthalene dimer, showing that π-π stacking interactions become significant for bicyclic and larger PAHs.

Plumbing Potentials for Molecules with Up To Tens of Atoms: How to Find Saddle Points and Fix Leaky Holes.

Potential energy surfaces (PESs) play an indispensable role in molecular dynamics but are notoriously difficult to flesh out properly in large-dimensional spaces. In particular, the undetected presence of PES holes, i.e., unphysical saddle points beyond which the potential energy drops arbitrarily, can have devastating effects on both classical and quantum dynamics calculations. In this study, the Crystal algorithm is developed as a tool for efficiently and accurately finding PES holes, as well as legitimate saddle points, even in very large-dimensional configuration spaces. The approach is applied to three large-dimensional PESs for molecular systems of current interest: uracil, naphthalene, and formic acid dimer. Low-lying PES holes are discovered and located for the first two systems-including naphthalene, for which no holes were previously suspected, to the best of our knowledge. Likewise, the double-well, double-proton-transfer isomerization saddle point for formic acid dimer is also located.

Photo-dissociation of naphthalene dimer cations stored in a compact electrostatic ion storage ring.

Naphthalene dimer cations [C10H8]2 + have been produced by using an electron cyclotron resonance plasma ion source and stored in a compact electrostatic ion storage ring. We show that the radiative cooling of these cations is much slower than the isolated monomer naphthalene cations. We also report on photo-dissociation studies in the gas phase of naphthalene dimer cations at high internal energy. The dissociation energy is estimated to 0.5 eV in close agreement with previous measurements but a factor of 2 smaller than recent (density functional theory (DFT) and ab initio) theoretical studies. As uncertainties on theory as well as on the experiment cannot be as large as this difference, we conclude that this discrepancy may be due to temperature effects with possible isomerization. As an interpretation of the photo-dissociation spectrum of naphthalene dimer cations, we propose a tentative simple analytical model based on effective Morse potentials. These effective potentials are expected to "average" temperature effects that would apparently result in a smaller energy difference between the fundamental and dissociation states due to the twisting vibration modes of the naphthalene dimer cations.

Stability of dimer and trimer of Naphthalene studied in electrostatic storage Mini-Ring.

SynopsisWe report studies on stabilities of dimer and trimer of polycyclic aromatic hydrocarbon PAH in a small electrostatic storage device. Different nslaser energies were used at different time delays as the probe to determine the dissociation energy. The effect of dehydrogenation on the stability is also studied.

Accurate calculations of the noncovalent systems with flat potential energy surfaces: Naphthalene dimer and azulene dimer

It is very challenging to construct the potential energy surfaces for the medium and large noncovalent systems employing the coupled clusters with singles, doubles, and perturbative triples, CCSD(T), at the complete basis set (CBS) limit. The main obstacle lies in the time-consuming and expensive CCSD(T) optimizations of the geometries. One method to overcome the obstacle is to use the cheap density functional theory with the D3 dispersion correction (DFT-D3) instead of the CCSD(T) method to optimize the geometries of the noncovalent systems. In the present study, the potential energy surfaces of the naphthalene dimer and azulene dimer were investigated using a combined DFT-D3 optimization and single-point CCSD(T)/CBS energy calculation scheme. The results clearly show that this scheme can give highly accurate CCSD(T)/CBS potential energy surfaces for the naphthalene dimer and the azulene dimer.

The photophysics of naphthalene dimers controlled by sulfur bridge oxidation.

In this study we investigate in detail the photophysics of naphthalene dimers covalently linked by a sulfur atom. We explore and rationalize how the oxidation state of the sulfur-bridging atom directly influences the photoluminescence of the dimer by enhancing or depriving its radiative and non-radiative relaxation pathways. In particular, we discuss how oxidation controls the amount of electronic transfer between the naphthalene moieties and the participation of the SO n bridge in the low-lying electronic transitions. We identify the sulfur electron lone-pairs as crucial actors in the non-radiative decay of the excited sulfide and sulfoxide dimers, which are predicted to proceed via a conical intersection (CI). Concretely, two types of CI have been identified for these dimers, which are associated with the photo-induced pyramidal inversion and reverse fragmentation mechanisms found in aryl sulfoxide dimers. The obtained results and conclusions are general enough to be extrapolated to other sulfur-bridged conjugated dimers, therefore proportionating novel strategies in the design of strongly photoluminescent organic molecules with controlled charge transfer.

A Theoretical Investigation of the Structure and Optical Properties of a Silver Cluster in Solid Form and in Solution.

Using density functional theory (DFT) and linear and quadratic response time-dependent DFT, we investigated the structure and optical properties of a silver sulfide cluster with the interesting property of dual emission that was observed when in crystal form but not in solution. Since the dual fluorescence is observed only in the crystal, a supposition of stabilization of a higher-energy excited state by an excimer-like complex was analyzed by calculations for a cluster dimer, formed through π-stacking of aromatic groups bonded to the sulfur atoms. However, because of the complexity of the system, a simple one-dimensional method for dimer optimization, which works moderately well in predicting the red-shifted fluorescence compared to its absorption in a naphthalene dimer, predicts only partially the red shift for the emission energy. Interestingly, calculations of the two-photon absorption (TPA) cross-section on the optimized isolated cluster as well as the crystal structure geometry indicate significant off-resonance TPA. While some materials have significantly larger TPA cross-sections, such a TPA cross-section off-resonance could be useful. The high density of states in the dimer system results in a higher probability for significant resonance enhancement and thus much larger TPA cross-sections.

Stability and partial oligomerization of naphthalene under high pressure at room temperature

The stability and pressure-induced chemical reactions of naphthalene were investigated at room temperature at pressures up to 23GPa. In-situ X-ray diffraction (XRD) measurements indicated that naphthalene retained its crystal structure up to ∼20GPa, whereas a solid amorphous phase was observed in the recovered samples. Based on microanalysis of the recovered samples using Gas Chromatograph Mass Spectrometer (GC/MS), naphthalene dimer and trimer isomers were observed at pressures exceeding 15GPa. The dimers were classified as products of simple dimerization, naphthylation, and condensation, similar to the case of the pressure-induced dimerization of benzene, indicating a similar dimerization mechanism for naphthalene.

Structures and Binding Energies of the Naphthalene Dimer in Its Ground and Excited States.

Possible structures of the naphthalene dimer corresponding to local energy minima in the ground and excited (excimer) electronic states are comprehensively investigated using DFT-D and TDDFT-D methods with a special accent on the excimer structures. The corresponding binding and electronic transition energies are calculated, and the nature of the electronic states in different structures is analyzed. Several parallel (stacked) and T-shaped structures were found in both the ground and excited (excimer) states in a rather narrow energy range. The T-shaped structure with the lowest energy in the excited state exhibits a marked charge transfer from the upright molecule to the base one.

Defining the contributions of permanent electrostatics, Pauli repulsion, and dispersion in density functional theory calculations of intermolecular interaction energies.

In energy decomposition analysis of Kohn-Sham density functional theory calculations, the so-called frozen (or pre-polarization) interaction energy contains contributions from permanent electrostatics, dispersion, and Pauli repulsion. The standard classical approach to separate them suffers from several well-known limitations. We introduce an alternative scheme that employs valid antisymmetric electronic wavefunctions throughout and is based on the identification of individual fragment contributions to the initial supersystem wavefunction as determined by an energetic optimality criterion. The density deformations identified with individual fragments upon formation of the initial supersystem wavefunction are analyzed along with the distance dependence of the new and classical terms for test cases that include the neon dimer, ammonia borane, water-Na(+), water-Cl(-), and the naphthalene dimer.