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The photophysical properties of a series of recently synthesized single benzene fluorophores were investigated using ensemble density functional theory calculations. The energetic stability of the ground and excited state species were counterposed against the aromaticity index derived from local vibrational modes. It was found that the large Stokes shift of the fluorophores (up to ca. 5800 cm −1) originates from the effect of electron donating and electron withdrawing substituents rather than π‐delocalization and related (anti‐)aromaticity. On the basis of nonadiabatic molecular dynamics simulations, the absence of fluorescence from one of the regioisomers was explained by the occurrence of easily accessible S 1/S 0 conical intersections below the vertical excitation energy level. It is demonstrated in the manuscript that the analysis of local mode force constants and the related aromaticity index represent a useful tool for the characterization of π‐delocalization effects in π‐conjugated compounds. [ABSTRACT FROM AUTHOR]

Molecular emitters simultaneously generating light at different wavelengths have wide applications. With a small molecule, however, it is challenging to realize two independent radiative pathways. We invented the first examples of dual‐emissive single‐benzene fluorophores (SBFs). Two emissive tautomers are generated by synthetic modulation of the hydrogen bond acidity, which opens up pathways for excited‐state proton transfer. White light is produced by a delicate balance between the energy and intensity of the emission from each tautomer. We show that the excited‐state antiaromaticity of the benzene core itself dictates the proton movements driving the tautomer equilibrium. Using this simple benzene platform, a fluorinated SBF was synthesized with a record high solubility in perfluorocarbon solvents. White light‐emitting devices and multicolor imaging of perfluorocarbon nanodroplets in live cells demonstrate the practical utility of these molecules. [ABSTRACT FROM AUTHOR]

The formulations and performances of spin‐restricted ensemble‐referenced KS and mixed‐reference spin‐flip time‐dependent density functional theory incorporating strong correlations into density functional theories are documented. As a result of balanced dynamic and nondynamic correlation, they are capable of describing strongly correlated challenging systems including diradicals, bond dissociation, conical intersections, doubly excited states, and so on, overcoming the limitations of current density functional theories. [ABSTRACT FROM AUTHOR]

The utility of the QTAIM/stress tensor analysis method for characterizing the photoisomerization of light driven molecular rotary machines is investigated on the example of the torsion path in fluorene molecular motor. The scalar and vector descriptors of QTAIM/stress tensor reveal additional information on the bonding interactions between the rotating units of the motor, which cannot be obtained from the analysis of the ground and excited state potential energy surfaces. The topological features of the fluorene motor molecular graph display that, upon the photoexcitation a certain increase in the torsional stiffness of the rotating bond can be attributed to the increasing topological stability of the rotor carbon atom attached to the rotation axle. The established variations in the torsional stiffness of the rotating bond may cause transfer of certain fraction of the torsional energy to other internal degrees of freedom, such as the pyramidalization distortion. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Ensemble density functional theory ( DFT) is a novel theoretical approach that is capable of exact treatment of non-dynamic electron correlation in the ground and excited states of many-body fermionic systems. In contrast to ordinary DFT, ensemble DFT has not found so far a way to the repertoire of methods of modern computational chemistry, probably owing to the lack of practically affordable implementations of the theory. The spin-restricted ensemble-referenced Kohn-Sham ( REKS) method represents perhaps the first computational scheme that makes ensemble DFT calculations feasible. The REKS method is based on the rigorous ensemble representation of the energy and the density of a strongly correlated system and provides for an accurate and consistent description of molecular systems the electronic structure of which is dominated by the non-dynamic correlation. This includes the ground and excited states of molecules undergoing bond breaking/bond formation, the low-spin states of biradicals and polyradicals, symmetry forbidden chemical reactions and avoided crossings of potential energy surfaces, real intersections between the energy surfaces of the ground and excited states (conical intersections), and many more. The REKS method can be employed in connection with any local, semi-local and hybrid (global and range-separated) functional and affords calculations of large and very large molecular systems at a moderate mean-field cost. WIREs Comput Mol Sci 2015, 5:146-167. doi: 10.1002/wcms.1209 Conflict of interest: The author has declared no conflicts of interest for this article. For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

Dirac-exact relativistic methods, i.e., 2- or 1-component methods which exactly reproduce the one-electron energies of the original 4-component Dirac method, have established a standard for reliable relativistic quantum chemical calculations targeting medium- and large-sized molecules. Their development was initiated and facilitated in the late 1990s by Dyall's development of the normalized elimination of the small component ( NESC). Dyall's work has fostered the conversion of NESC and related (later developed) methods into routinely used, multipurpose Dirac-exact methods by which energies, first-order, and second-order properties can be calculated at computational costs, which are only slightly higher than those of nonrelativistic methods. This review summarizes the development of a generally applicable 1-component NESC algorithm leading to the calculation of reliable energies, geometries, electron density distributions, electric moments, electric field gradients, hyperfine structure constants, contact densities and Mössbauer isomer shifts, nuclear quadrupole coupling constants, vibrational frequencies, infrared intensities, and static electric dipole polarizabilities. In addition, the derivation and computational possibilities of 2-component NESC methods are discussed and their use for the calculation of spin-orbit coupling ( SOC) effects in connection with spin-orbit splittings and SOC-corrected energies are demonstrated. The impact of scalar relativistic and spin-orbit effects on molecular properties is presented. WIREs Comput Mol Sci 2014, 4:436-467. Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

The normalized elimination of the small component method is a first principles two-component relativistic approach that leads to the Dirac-exact description of one-electron systems. Therefore, it is an ideal starting point for developing procedures, by which first- and second-order response properties can be routinely calculated. We present algorithms and methods for the calculation of molecular response properties such as geometries, dipole moments, hyperfine structure constants, vibrational frequencies and force constants, electric polarizabilities, infrared intensities and so forth. The described formalisms are applied to molecules containing mercury and other heavy elements, which require a relativistic treatment. Perspectives for the future development and application of Dirac-exact methods are outlined. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The design and synthesis of artificial molecular motors to power up the nanoscale mechanical devices is one of the urgent tasks for modern synthetic chemistry. Light-driven molecular rotary motors are a key class of compounds that undergo unidirectional rotation about a double bond through a series of photochemical and thermal steps. To improve their functionality and to develop new design strategies, a deeper understanding of the dynamics behind light-driven rotary motion is required. Such an understanding can be only gained from the accurate dynamics simulations of the nonadiabatic photo-rearrangement processes occurring during the motor operation. The currently available methods of quantum chemistry combined with the nonadiabatic molecular dynamics techniques represent a powerful tool for the investigation of the dynamic aspects of the molecular motors functionality. The results obtained in theoretical simulations provide for an unprecedented understanding of the photoisomerization process and hold considerable implications in achieving improved design strategies for future generations of molecular motors. © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multireference averaged quadratic coupled cluster (MRAQCC) (4,5)/cc-pVTZ calculations predict that bond pseudorotation (BPR) in the first excited singlet state of the cyclopentadienyl cation (CPC) proceeds with a barrier of just 0.35 kcal/mol, where five dienylic forms present the minima and five allylic forms the transition states of the pseudorotation process. Vibrational and entropic corrections revert the order of stabilities and lead to a Δ G(298) of just 0.05 kcal/mol indicating that BPR is unhindered at room temperature. The description of the CPC ring in terms of curvilinear deformation coordinates (seven for C5, seven for X5, and three coupling coordinates) make it possible to explore both the six-dimensional (6D) Jahn-Teller and the 8D pseudo-Jahn-Teller space and assess the importance of Jahn-Teller and pseudo-Jahn-Teller deformations of the CPC ring. The latter dominate the ring deformations along the BPR path. The only somewhat larger Jahn-Teller contribution results from a E [ABSTRACT FROM AUTHOR]

Next‐generation quantum theory of atoms in molecules was applied to analyze, along an entire bond path, intramolecular interactions known to influence the photoisomerization dynamics of a light‐driven rotary molecular motor. The 3D bond‐path framework set B0,1 constructed from the least and most preferred directions of electronic motion, provided new insights into the bonding leading to different S1 state lifetimes including the first quantification of covalent character of a closed‐shell intramolecular bond path. We undertook the first use of the stress tensor trajectory Tσ(s) analysis on selected nonadiabatic molecular dynamics trajectories with the electron densities obtained using the ensemble density functional theory method. The stress tensor Tσ(s) analysis was found to be well suited to follow the dynamics trajectories that included the S0 and S1 electronic states through the conical intersection and also provided to a new measure to assess the degree of purity of the axial bond rotation for the design of rotary molecular motors. [ABSTRACT FROM AUTHOR]

The conical intersections corresponding to the C─O and C─C ring opening were optimized and the reaction paths traversing these intersections were obtained. Investigation of the C─O ring opening revealed that when traversing the lowest energy conical intersection, the reaction path returns to the closed ring geometry. The C─O path traversing the intersection featuring torsion of terminal CH2 group however, led to a ring‐opened geometry, an H‐shift and the formation of acetaldehyde that can undergo further dissociation. The observation of different reaction paths was explained by the 3‐D paths from quantum theory of atoms in molecules (QTAIM) that defined the most preferred direction of electronic motion that precisely tracked the mechanisms of bond breaking and formation throughout the photo‐reactions. The size, orientation, and location of these most preferred 3‐D paths indicated the extent and direction of motion of atoms, bonds, and the degree of torsion or planarity of a bond indicating a predictive ability. [ABSTRACT FROM AUTHOR]

A balanced treatment of the covalent and ionic contributions to the ground and excited states originating from torsion about double bonds is known to be strongly dependent on the presence of dynamic electron correlation. We undertake an analysis of the minimum energy pathways corresponding to deactivation of the first excited singlet state of PSB3. In doing so we consider torsion about the three double bonds including other intramolecular degrees of freedom, such as the bond length alternation. The 3‐D bond‐path analysis provides a new 'bond‐localized orbital‐like' directional interpretation of bonding. Therefore, we present a more sophisticated method of determination of the degree of covalent and ionic contributions known to be responsible for altering the relative stability of the S1/S0 conical intersections. The results presented suggest that the commonly used simplified multi‐reference methodologies that often result in incorrect predictions for the excited state deactivation reaction mechanism. The bond‐path framework set B visualization of the spectrum of the chemical character (covalent–biradical‐ionic) displayed of each of the back‐bone bonds as well as the influence on neighboring bonds. The most preferred directions of accumulation of charge density, q‐ and q′‐paths along the backbone bond‐path (r) corresponding to the torsional C10‐N12 BCP for the S0 (top) and S1 (below) states at a value of the torsion q = 90.0°. [ABSTRACT FROM AUTHOR]

The factors underlying the experimentally observed branching ratio (70:30) of the (1,3‐cyclohexadiene) CHD → HT (1,3,5‐hexatriene) photochemical ring‐opening reaction are investigated. The ring‐opening reaction path is optimized by a high‐level multi‐reference DFT method and the density along the path is analyzed by the quantum theory of atoms in molecules (QTAIM) and stress tensor methods. The performed density analysis suggests that, in both S1 and S0 electronic states, there exists an attractive interaction between the ends of the fissile σ‐bond of CHD that steers the ring‐opening reaction predominantly in the direction of restoration of the ring. It is suggested that opening of the ring and formation of the reaction product (HT) can only be achieved when there is a sufficient persistent nuclear momentum in the direction of stretching of the fissile bond. As this orientation of the nuclear momentum vector can be expected relatively rare during the dynamics, this explains the observed low quantum yield of the ring‐opening reaction. Experimentally observed branching ratio (70:30) of the (1,3‐cyclohexadiene) CHD → HT (1,3,5‐hexatriene) photochemical ring‐opening reaction is investigated by first‐principles calculations and next‐generation quantum theory of atoms in molecules. It is suggested that opening of the ring and formation of the reaction product can only be achieved when there is a sufficient persistent nuclear momentum in the direction of stretching of the fissile bond. [ABSTRACT FROM AUTHOR]

A vector‐based representation of the chemical bond is introduced, which we refer to as the bond‐path framework set B = {p, q, r}, where p, q, and r represent 3 eigenvector‐following paths with corresponding lengths H*, H, and the familiar quantum theory of atoms in molecules (QTAIM) bond‐path length (BPL). The intended application of B is for molecules subjected to various types of reactions and distortions, including photoisomerization reactions, applied torsions θ, or normal modes of vibration. The lengths H* and H of the eigenvector‐following paths are constructed using the e1 and e2 Hessian eigenvectors, respectively, along the bond path, these corresponding to the least and most preferred directions of charge density accumulation. In particular, the paths p and q provide a vector representation of the scalar QTAIM ellipticity ε. The bond‐path framework set B is applied to the excited state deactivation of fulvene that involves distortions along various intramolecular degrees of freedom, such as the bond stretching/compression of bond‐length alternation and bond torsion distortions. We find that the H* and H lengths can differentiate between the ground and excited electronic states, in contrast to the QTAIM BPL. Five unique paths were presented for B= {(p0,p1), (q0,q1), r} for the ground and first excited states where the profile of the scaling factor, the ellipticity ε, reveals a large unexpected asymmetry for the excited state. A "next‐generation" quantum theory of atoms in molecules (QTAIM) is introduced to analyze all types of bonding in molecules subjected to various types of reactions and distortions, including photoisomerization reactions, applied torsions θ, or normal modes of vibration. The double‐bond isomerization of fulvene is used as test model for this "next‐generation" QTAIM approach. [ABSTRACT FROM AUTHOR]