Integral Equation Formalism Polarizable Continuum Research Articles

Spectroscopic Characterization, Hirshfeld Surface, DFT, and TD-DFT of tert-Butyl Phenethylcarbamate and 1,1-Dimethyl-3-Phenethylurea

Tert-butylphenethylcarbamate (1) and 1,1-dimethyl-3-phenethylurea (2) were synthesized, and their structures were confi rmed by NMR, FTIR, and mass spectrometry techniques. The experimental spectroscopic data of 1 and 2 were compared with the corresponding calculated ones obtained by density functional theory (DFT) and time-dependent DFT methods, for which the hybrid functionals B3LYP, B3P86, and PBE0 combined with the 6-311++G(d,p) basis set were tested. The solvent effect was considered using the implicit model — integral equation formalism-polarizable continuum model (IEFPCM). Relatively good correlation (R2 > 90%) was obtained between the experimental and predicted spectral data. The conformational effect on the absorption maximum λmax was negligible, that is, λmax of different conformers varied by less than 0.01 nm. Hirshfeld surface analysis and electrostatic potential calculations of the closest intermolecular contacts between active atoms of 1 and 2 revealed that the closest interactions were between hydrogen atoms of 39.6 and 46.3%, respectively.

Hydrogen bond interactions of hydrated aluminum nitrate with PVDF, PVDF‐TrFE, and PVDF‐HFP: A density functional theory‐based illustration

AbstractHydrogen bond (HB) interaction is the main driving factor for the nucleation of electroactive β phase within the nonpolar pristine polyvinylidene fluoride (PVDF) and its copolymers when the hydrated nitrate salts act as additives. The current work elaborates a density functional theory‐based analysis on the HB interactions within aluminum nitrate nonahydrate‐added polyvinylidene fluoride [PVDF/Al(NO3)3∙9H2O], polyvinylidene fluoride‐trifluoro ethylene [PVDF‐TrFE/Al(NO3)3∙9H2O], and polyvinylidene fluoride‐hexafluoro propylene [PVDF‐HFP/Al(NO3)3∙9H2O] composite systems. Polar properties of α (TGTG′) and β (TTTT) phases of the homopolymer and copolymer chains have been compared. Coordination chemistry and formation energies of two stable isomers of Al(NO3)3∙9H2O have been described. Interactions within the polymer/salt complexes have been simulated considering both the salt isomers added to α‐ and β‐tetramer chains of PVDF, PVDF‐TrFE, and PVDF‐HFP. An integral equation formalism polarizable continuum model has been used to replicate the effects of n,n‐dimethyl formamide solvent. HB interaction phenomenon has been described on the basis of electron density difference, interaction energy calculations, symmetry‐adapted perturbation theory, natural bond orbital, Bader's quantum theory of atoms in molecules, delocalization indices, and reduced density gradient analyses. Simulated infra red (IR) and Raman spectra identified the simultaneous presence of CH⋯O (mostly improper) and OH⋯F (mostly proper) HBs between the salt molecule and polymer chains. Correlations among different HB descriptors have been demonstrated to compare the proper and improper nature of the bonds. This research explored some ambiguities in the conventional HB properties, which may be attributed to very low hyperconjugation energies associated with the bonds.

Synthesis, crystal structure, Hirshfeld surface analysis, spectral characterization, and quantum computational evaluation of (E)-2-(((4-bromophenyl)imino)methyl)-6-methylphenol

A newly synthesized compound, (E)-2-(((4-bromophenyl)imino)methyl)-6-methylphenol (C14H12BrNO), is analyzed in detail for structural clarification by experimental X-ray, Fourier transform IR, 1H and 13C NMR, and UV–vis spectral data along with theoretical quantum chemical computations. For the theoretical computations, the density functional theory B3LYP functional and 6–311++G (d,p) basis set were used in the gas phase, and the harmonic vibrational wavenumbers were assigned with the help of the potential energy distribution. The theoretical NMR spectra were obtained with the gauge-including atomic orbital (GIAO) method and for the UV–vis spectrum time-dependent density functional theory based on the integral equation formalism polarizable continuum model (IEFPCM) was used. By Hirshfeld surface analysis, the most important contributions were obtained for the crystal packing, and the possible contact points were determined. In addition, frontier molecular orbital (highest occupied molecular orbital–lowest unoccupied molecular orbital), molecular electrostatic potential, and nonlinear optical analyses were performed for the calculated optimized structure. Finally, molecular docking between (E)-2-(((4-bromophenyl)imino)methyl)-6-methylphenol and two different receptors (ubiquinol-cytochrome c reductase [Protein Data Bank ID 1BE3] and glucan endo-1,6-β-glucosidase [Protein Data Bank ID 5NGL]) was studied. From the results, (E)-2-(((4-bromophenyl)imino)methyl)-6-methylphenol was determined to be a good ubiquinol-cytochrome c reductase inhibitor because of its binding energy and affinity for protein active sites.

Prediction of the half-lives of polychlorinated biphenyls based on the IEF-PCM calculations

Three-dimensional structures of 62 polychlorinated biphenyl (PCB) congeners were optimized with the integral equation formalism polarizable continuum model (IEF-PCM) in combination with the density functional theory (DFT) method at 6-31G(d) level. By applying support vector machine (SVM) algorithm, a nonlinear quantitative structure–property relationship (QSPR) model was built to predict half-lives (log [Formula: see text]) of 62 PCBs in juvenile rainbow trout. The optimal SVM model based on the parameters [Formula: see text] of 854.721 and [Formula: see text] of 0.0565 produces the root-mean-square (rms) errors of 0.0352 for the training set and 0.0446 for the test set, which are less than that of the previous models reported. The results suggest that it is feasible to build SVM models for the half-lives of PCBs with IEF-PCM and B3LYP/6-31G(d) for deriving structural descriptors.

DFT Quantum Chemical Studies on Structural, Nonlinear Optical, Reactivity and Thermodynamic Properties of 4‐Methoxy‐2‐{(E)‐[(thiophen‐2‐yl)ethylimino]methyl}phenol

AbstractThe molecular structure of 4‐Methoxy‐2‐{(E)‐[(thiophen‐2‐yl)methylimino]methyl}phenol was optimized using the PBEPBE, B3PW91 and B3LYP methods with the 6–311++G(d,p) basis set and compared to experimental X‐ray data. Density functional computations of the interaction energies, molecular electrostatic potential, and thermodynamic functions have been carried out using the B3LYP method with the 6–311++G(d,p) basis set for the title molecule. The chemical reactivity behaviors of the tautomeric forms of the compound were analyzed at the B3LYP/6‐311++G(d,p) level. Additionally, the solvent effects have been investigated with the integral equation formalism polarizable continuum model. The dipole moment, first hyperpolarizability and linear polarizability values of the tautomeric forms of the compound were computed using the B3LYP/6‐311++G(d,p) method. The changes of the entropy, enthalpy and Gibbs free energy for the formation reaction of the compound have been predicted in different temperature utilizing the statistical thermodynamical technique.

Prediction of Depuration Rate Constants for Polychlorinated Biphenyl Congeners.

The integral equation formalism polarizable continuum model (IEF-PCM) for solvent effects with the default solvent (water) and solvent parameters, together with the density functional theory method at 6-31G(d) level, was used to optimize molecular structures for polychlorinated biphenyl (PCB) congeners. Four molecular descriptors were selected to develop quantitative structure–activity relationship (QSAR) models for the depuration rate constants (kd) of 63 PCB congeners in a juvenile rainbow trout (Oncorhynchus mykiss). The optimal multiple linear regression (MLR) model has the correlation coefficient R of 0.933 and the root mean square (rms) error of 0.0681 for the total set of 63 PCB congeners. The support vector regression model has R of 0.953 and rms error of 0.0576 for the total set. Both the MLR and SVM QSAR models in this paper were accurate and acceptable compared with other QSAR models for the depuration rate of PCB congeners reported in references. Thus, applying IEF-PCM and B3LYP/6-31G(d) calculations for molecular descriptor derivation of PCB congeners is successful.

Nonbonding interaction analyses on PVDF/[BMIM][BF4] complex system in gas and solution phase.

The present study provides a detailed quantum chemical description of the physicochemical interactions between poly-vinylidene fluoride (PVDF) and 1-butyl-3-methyl-imidazolium tetrafluoro borate ([BMIM][BF4]) ionic liquid (IL). Geometry optimization and frequency calculations are carried out for four monomer units of α- and β-PVDF, [BMIM][BF4], and PVDF/[BMIM][BF4] using dispersion corrected density functional theory. The effects of solvation on the systems under study are demonstrated for three polar aprotic solvents, namely tetra-hydrofuran (THF), acetone, and n,n-dimethyl formamide (DMF) using the integral equation formalism polarizable continuum model (IEFPCM). Calculated negative solvation free energy values suggest solution phase stability of the systems under study. Binding and interaction energies for β-PVDF/IL are found higher in magnitude than those for α-PVDF/IL. The nonbonding interaction phenomenon of β-PVDF/[BMIM][BF4] is elucidated on the basis of natural bond orbital (NBO), Bader's quantum theory of atoms in molecules (QTAIM), delocalization indices, Hirshfeld surface, and reduced density gradient (RDG) analyses. Both anions and cations of ionic liquids are found to show weak van der Waals interaction with PVDF molecule but the anion ([BF4]-)/PVDF interaction is found to be stronger than cation ([BMIM]+)/PVDF interaction. Inter-unit C-H⋯F type hydrogen bonds are found to show improper (causing blue shifts in vibrational frequencies) nature. Frontier molecular orbital analysis is carried out, and different chemical parameters like electronegativity, chemical potential, chemical hardness and softness, and electrophilicity index are calculated using Koopmans' theorem. Thermochemical calculations are also performed, and the variation in different standard thermodynamic parameters with temperature is formulated. Graphical abstract (a) Hirshfeld surface mapped onto electron density and (b) NCI isosurfaces showing inter-unit interactions of β-PVDF/[BMIM][BF4].

New diorganotin(IV) complexes of Schiff base derived from 4‐amino‐3‐hydrazino‐5‐mercapto‐4H‐1,2,4‐triazole: Synthesis, structural characterization, density functional theory studies, atoms‐in‐molecules analysis and antifungal activity

New diorganotin(IV) complexes of a Schiff base (HL) having general formula R2Sn(L)Cl (where L is the monoanion of HL and R = n‐Bu or Ph) have been synthesized and characterized using elemental analysis, infrared, NMR (1H, 13C, 119Sn) and UV–visible spectroscopies and mass spectrometry. These investigations suggest that in these 1:1 monomeric derivatives the Schiff base ligand acts in a monoanionic bidentate manner coordinating through the Ophenolic and Nazomethine, with proposed distorted trigonal bipyramidal geometry around tin with Ophenolic and two organic groups in the equatorial plane and the Nazomethine and the third organic group in axial positions. The proposed structures have been validated by density functional theory (DFT)‐based quantum chemical calculations at the B3LYP/6‐31G(d,p)/Def2‐SVP (Sn) level of theory. The simulated UV–visible spectrum was obtained with the time‐dependent DFT method in the gas phase and in the solvent field with the integral equation formalism–polarizable continuum model. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates a good correlation between them. An insight into the intramolecular bonding and interactions among bonds in organotin(IV) complexes of HL was obtained by means of natural bond orbital analysis. The topological and energetic properties of the electron density distribution for the tin–ligand interaction in R2Sn(L)Cl have been theoretically calculated at the bonds around the central tin atom in terms of atoms‐in‐molecules theory. The R2Sn(L)Cl complexes were screened for their in vitro antifungal activity against chosen fungal strains.

Study of electronic and transport properties of melanin structure using Density Functional Theory

Organic semiconductors are a relatively new member of the semiconductor family and composed of molecules containing carbon, hydrogen, and another element. Melanin is a pigment that colours skin, eyes and hair and it could soon be facing a new generation of biologically friendly electronic devices in applications such as medical sensor and tissue stimulation treatment. The need to find the correct solvent for the melanin still remains challenged. In this work the electronic properties of eumelanin was studied under gas phase and solution, using Integral Equation Formalism Polarizable Continuum Model (IEFPCM) using different solvent. Total energy, Homo-Lumo energy gaps and density of states were reported. Gaussian09 code which uses density functional theory as the working principle was used to study the electronic and transport properties of melanin structure. Three exchange functional: HF (HF), GGA (PBE) and Hybrid (B3LYP) were used at different basis set of 3-21G, 6-31G, and 6-311G. It was found that at the 6-311G level for the three exchange functional, the total energy of -2981.03028, -2996.839821 and -3000.227297 eV respectively. However, HOMO-LUMO energy gap in gas phase was improved to be 2.65 eV and 2.79 eV, 2.65 eV in DMSO and Acetonitrile respectively. It was concluded that DMSO solvent is more efficient for melanin compound. However, it is recommended to increase the level of approximation.

New bis 1,3,4-oxadiazole derivatives: syntheses, characterizations, computational studies, and antioxidant activities

In this study, two new bis oxadiazole derivatives (2a and 2b) were synthesized. The new compounds were characterized by elemental analyses, IR, 1H NMR, 13C NMR, and mass spectral studies and were tested for their antioxidant activity. According to the results, it was observed that the synthesized compounds (2a and 2b) had a very high activity in both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing ability of plasma (FRAP) tests. The approximate geometries of the compounds 2a and 2b were prepared with GaussView5 visualization program. The optimized molecular geometric parameters, vibrational wavenumbers, UV–vis parameters, and HOMO–LUMO simulations were computed using Gaussian 09W program. The computations were performed at 6-311++G(d,p) basis set using the B3LYP functional in density functional theory (DFT) method. The harmonic vibrational wavenumbers computed in gas phase were scaled with 0.958 (1700–4000 cm−1) and 0.983 (0–1700 cm−1) for the B3LYP/6-311++G(d,p) level. To calculated the UV–vis spectroscopic parameters with TD-DFT method, the compounds 2a and 2b were optimized in DMF and DMSO solvents using the integral equation formalism polarizable continuum model (IEFPCM) method at the B3LYP/6-311++G(d,p) level. The HOMO, LUMO, and UV–vis analyses were studied to interpret intramolecular charge transfers.

DFT studies of camptothecin aggregation in solutions

The structures of camptothecin (CPT) lactone head-to-tail π-aggregates up to tetramers were optimized in DMSO and aqueous solutions using various DFT functionals with cc-pVDZ basis sets. Solvent effects were estimated using the Integral Equation Formalism Polarizable Continuum Model. The calculated reaction equilibria indicate that the higher π-aggregates formation is more preferred in DMSO than in aqueous solutions. TD-B3LYP calculated electron transitions ascribe two strong peaks over 300 nm in UV–Vis spectra to the CPT monomer (at lower wavelength) and to higher CPT head-to-tail π-aggregates (at higher wavelengths). Only B3LYP with D2 dispersion correction of Grimme and ωB97XD functionals are able to produce reliable results.

Molecular structure and absorption spectral properties of Corrole Isomers: DFT and TDDFT-IEFPCM investigations

Corrole has become one of the most important branches of porphyrin chemistry for the better optical properties than traditional porphyrin. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been utilized to simulate the molecular structures and electron absorption spectra of corrole and isomers. The molecular structure and charge distribution results revealed that the inner hydrogen atoms of the homologous isomers exhibit similar charge distribution. The corrole isomers show better absorption than corrole in Q band due to the carbon-nitrogen-swap structure, especially in isomers NCC1/NCC2. The diverse Q bands illuminate that the light absorption performance of corrole isomers vary in different polarity solvents based on the integral equation formalism polarizable continuum model (IEF-PCM) results. Obviously variations of NCC5 and NCC6 spectra in the three solvents indicated that both isomers are sensitive to the polarity of solvents and could be applied to regulate the light absorption ability of them by adjusting the polarity of the solvent. These theoretical researches would be conducive to the molecular design of novel multi-band photon absorption corrole isomers.

Spectroscopic (FT-IR, Laser-Raman and NMR) and conformational analysis on novel pyrazole β-keto ester compound

Our goal in this study is to submit a comprehensive theoretical study of novel compound. Therefore, we perused and analyzed the experimental (real form) and theoretical (gas form) vibrational frequencies for the most stable conformer of title compound. The crystallographic geometry was used for full geometry optimization, followed by a conformational analysis. The experimental FT-IR and Laser-Raman spectra of the studied molecule were taken in the region (4000-400 cm−1) and (4000-100 cm−1) in gas phase, respectively. For the most stable conformer, the vibrational modes and their assignments and optimized structure parameters (bond lengths, bond angles) were computed by using DFT/B3LYP functional and 6-311++G(d,p) basis set. Gaussian 09W software and GaussView5 interface programs were utilized for all computations. Theoretical mode assignments of the most stable conformer were obtained by using potential energy distribution (PED) with free VEDA 4 software program. The observed FT-IR and Laser-Raman spectra were compared with the calculated theoretical data. The computed vibrational frequencies of C1 conformer were also found in good agreement with the experimental results. The Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) analysis divulge the possibility of charge transfer within the molecule. The proton (1H) and carbon-13 (13C) nuclear magnetic resonance (NMR) chemical shifts were researched for the most stable conformer C1, both experimentally in DMSO-d6 and theoretically in DMSO with integral equation formalism polarizable continuum model (IEFPCM) method.

Revealing the Conformational Preferences of Proteinogenic Glutamic Acid Derivatives in Solution by 1H NMR Spectroscopy and Theoretical Calculations.

The conformational preferences of proteinogenic glutamic acid esterified (GluOMe) and N-acetylated (AcGluOMe) derivatives have been determined in solution for the first time. Theoretical calculations at the ωB97X-D/aug-cc-pVTZ made possible the assignment of six and eight stable conformers for GluOMe and AcGluOMe, respectively. The conformational equilibrium of the studied compounds was evaluated in different organic solvents using a combination of the integral equation formalism polarizable continuum model (IEF-PCM) and 1H NMR spectroscopy data. The results showed that the conformational equilibrium of both derivatives change in the presence of solvent. According to the quantum theory of atoms in molecules (QTAIM), non-covalent interactions (NCI), and natural bond orbitals (NBO) analyses, the conformational preferences observed for GluOMe and AcGluOMe are not dictated by the presence of a specific interaction but are due to a combination of hyperconjugative and steric effects.

Mono, di, tri and tetraethylene glycol: Spectroscopic characterization using density functional method and experiment

We report infrared and electronic absorption spectra of mono, di, tri and tetra ethylene glycol (EG) in gas phase, their cation and anion and in water solvent using density functional theory calculations at B3LYP/TZVP level. Structural paramaters, rotational and centrifugal distortional constants and dipole moments are also reported. A siginificant shifts in vibrational frequencies and peaks in electronic absorption spectra have been observed upon ionization of mono, di, tri and tetra ethylene glycols. We have also obtained experimental vibrational spectrum of monoethylene glycol. Vibrational frequencies of mono ethylene glycol from theory and experiment are compared. We have used integral equation formalism polarizable continuum model (IEFPCM) model to study the influence of water solvent on vibrational frequencies of neutral mono, di, tri and tetra ethylene glycol. Electronic absorption spectra for these molecules have been obtained using Time dependent density functional theory (TDDFT).

Prediction of the reduction potential in transition-metal containing complexes: How expensive? For what accuracy?

Accurate computationally derived reduction potentials are important for catalyst design. In this contribution, relatively inexpensive density functional theory methods are evaluated for computing reduction potentials of a wide variety of organic, inorganic, and organometallic complexes. Astonishingly, SCRF single points on B3LYP optimized geometries with a reasonably small basis set/ECP combination works quite well--B3LYP with the BS1 [modified-LANL2DZ basis set/ECP (effective core potential) for metals, LANL2DZ(d,p) basis set/LANL2DZ ECP for heavy nonmetals (Si, P, S, Cl, and Br), and 6-31G(d') for other elements (H, C, N, O, and F)] and implicit PCM solvation models, SMD (solvation model based on density) or IEFPCM (integral equation formalism polarizable continuum model with Bondi atomic radii and α = 1.1 reaction field correction factor). The IEFPCM-Bondi-B3LYP/BS1 methodology was found to be one of the least expensive and most accurate protocols, among six different density functionals tested (BP86, PBEPBE, B3LYP, B3P86, PBE0, and M06) with thirteen different basis sets (Pople split-valence basis sets, correlation consistent basis sets, or Los Alamos National Laboratory ECP/basis sets) and four solvation models (SMD, IEFPCM, IPCM, and CPCM). The MAD (mean absolute deviation) values of SCRF-B3LYP/BS1 of 49 studied species were 0.263 V for SMD and 0.233 V for IEFPCM-Bondi; and the linear correlations had respectable R2 values (R2 = 0.94 for SMD and R2 = 0.93 for IEFPCM-Bondi). These methodologies demonstrate relatively reliable, convenient, and time-saving functional/basis set/solvation model combinations in computing the reduction potentials of transition metal complexes with moderate accuracy. © 2017 Wiley Periodicals, Inc.

Synthesis, crystal structure, spectroscopic characterization and theoretical calculations of (Z)-N-(naphthalen-2-yl)-1-(5-nitrothiophen-2-yl)methanimine

The newly synthesized Schiff base compound, (Z)-N-(naphthalen-2-yl)-1-(5-nitrothiophen-2-yl)methanimine, C15H10N2O2S, was characterized by IR, UV–Vis and X-ray diffraction technique. All of the theoretical calculations have been calculated at the LSDA, BVP86, B3LYP and B3PW91 levels of the density functional method (DFT) with the 6–311++G(d,p) basis set by Gaussian software. UV–Visible absorption spectra of the title compound dissolved in ethanol were recorded and computed using the time dependent density functional theory (TD-DFT). The harmonic vibrational frequencies of the title compound were calculated using the same methods. So as to determine most favorable conformation as theoretically, molecular energy profile of the title compound were obtained as a function of the selected torsion angle by steps of 10° in the range of −180° to +180° rotation around the bond. The conformational analysis is a relationship between the energy of the title compound and its geometry. It is demonstrated that comparison between the calculated and experimental results provide a very good agreement. The energetic behavior such as the total energy, atomic charges, dipole moment of the title compound in solvent media were examined using the same methods by applying the Onsager and the integral equation formalism polarizable continuum model (IEF-PCM).

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and 3JHH coupling constant analyses.

The understanding of the conformational behavior of amino acids and their derivatives is a challenging task. Here, the conformational analysis of esterified and N-acetylated derivatives of L-methionine and L-cysteine using a combination of 1H NMR and electronic structure calculations is reported. The geometries and energies of the most stable conformers in isolated phase and taking into account the implicit solvent effects, according to the integral equation formalism polarizable continuum model (IEF−PCM), were obtained at the ωB97X-D/aug-cc-pVTZ level. The conformational preferences of the compounds in solution were also determined from experimental and theoretical 3JHH coupling constants analysis in different aprotic solvents. The results showed that the conformational stability of the esterified derivatives is not very sensitive to solvent effects, whereas the conformational equilibrium of the N-acetylated derivatives changes in the presence of solvent. According to the natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) and noncovalent interactions (NCI) methodologies, the conformational preferences for the compounds are not dictated by intramolecular hydrogen bonding, but by a joint contribution of hyperconjugative and steric effects.

Theoretical study of the Wittig, aza-Wittig and arsa-Wittig reactions of Me3P = XH ylide (X = CH, N and As) with cyclic ketones in the gas phase and solution phase

A computational study of the comparative reactivity of the Wittig, aza-Wittig and arsa-Wittig reactions of cyclopentanone and cyclobutanone with Me3P=XH ylide (X=CH, N and As) in the gas phase has been performed at B3LYP/6-31G∗∗ level of theory. Calculations have also been performed using integral equation formalism polarizable continuum model (IEFPCM), with THF solvent at B3LYP/6-31G∗∗ level of theory. In the gas phase as well as in solvent, these reactions were predicted to be two step processes with two complexes R and P (reactant complex and product complex), two transition states, one for addition (TS1) and the other for elimination (TS2) and two four-membered cyclic intermediates (INT1 and INT2), except that INT2 was not found in the aza-Wittig reaction. In our calculations, the Wittig reaction is found to be more favorable both thermodynamically and kinetically than aza- and arsa-Wittig reactions. The Wittig reaction is found to be more exothermic and to involve a lower activation barrier to formation of INT1 than the aza and arsa-Wittig reactions. The activation barriers in the reactions of cyclopentanone are higher as compared to the reaction of cyclobutanone in gas phase and solution phase. The addition activation barriers for each reaction are overestimated in the solvent model as compared to gas phase reactions.

Unusual Nonemissive Behavior of Rubrene J-Aggregates: A Rare Violation.

Structure-property correlations in rubrene (RB) colloidal J-aggregates were unravelled by steady state and time-resolved spectroscopy in conjunction with excited state density functional calculations. The RB J-aggregate with a slippage angle θ = 30.4°, estimated from the monomeric transition dipole moment directions, exhibited a broad fwhm of 1073 cm-1 and a 5 nm red-shifted absorption band carrying a transition dipole moment (M⃗λagg = 1.80 D) almost equivalent to the monomeric dye (M⃗λmon = 1.89 D). A significantly low magnitude of exciton coupling energy, ΔEexc = -358 cm-1 for the rhombic-RB colloidal J-aggregates resulted owing to the weaker electronic communication between the largely separated RB subunits (r = 7.2 Å) and a restricted exciton delocalization over the RB J-dimer (N = 2). The RB J-dimer exhibited a perfect balance between the computed singlet (2.53 eV) and the triplet (1.29 eV) exciton energies for singlet fission (SF). Supporting this, the PL decay profile of the J-aggregates revealed a delayed fluorescence, substantiating triplet pair formation via SF. The experimental evidence for the long-lived triplet formation was furthermore confirmed by its transient absorption (T1 → TN) at 530 nm. Consequently, a high probability for SF and a low probability for triplet-triplet recombination, leading to a dramatic lowering in photoluminescence quantum yield from 0.172 down to 0.035 was noted. The electronic structure calculations for the RB J-dimer followed TD-DFT-M062X/6-31G+(d,p) level of theory following integral equation formalism polarizable continuum model (IEFPCM) in water. S1 excited state for RB J-dimer was carefully analyzed using integral overlap of electron and hole density distribution (ϕ) and the defined t-indexes along all three spatial directions, and was found to be of locally excited in character.