| 1. |
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| 2. |
- Giussani, Angelo, et al.
(författare)
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Molecular Basis of the Chemiluminescence Mechanism of Luminol
- 2019
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Ingår i: Chemistry - A European Journal. - : WILEY-V C H VERLAG GMBH. - 0947-6539 .- 1521-3765. ; 25:20, s. 5202-5213
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Tidskriftsartikel (refereegranskat)abstract
- Light emission from luminol is probably one of the most popular chemiluminescence reactions due to its use in forensic science, and has recently displayed promising applications for the treatment of cancer in deep tissues. The mechanism is, however, very complex and distinct possibilities have been proposed. By efficiently combining DFT and CASPT2 methodologies, the chemiluminescence mechanism has been studied in three steps: 1)luminol oxygenation to generate the chemiluminophore, 2)a chemiexcitation step, and 3)generation of the light emitter. The findings demonstrate that the luminol double-deprotonated dianion activates molecular oxygen, diazaquinone is not formed, and the chemiluminophore is formed through the concerted addition of oxygen and concerted elimination of nitrogen. The peroxide bond, in comparison to other isoelectronic chemical functionalities (-NH-NH-, -N--N--, and -S-S-), is found to have the best chemiexcitation efficiency, which allows the oxygenation requirement to be rationalized and establishes general design principles for the chemiluminescence efficiency. Electron transfer from the aniline ring to the OO bond promotes the excitation process to create an excited state that is not the chemiluminescent species. To produce the light emitter, proton transfer between the amino and carbonyl groups must occur; this requires highly localized vibrational energy during chemiexcitation.
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| 3. |
- Manni, Giovanni Li, et al.
(författare)
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The OpenMolcas Web : A Community-Driven Approach to Advancing Computational Chemistry
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:20, s. 6933-6991
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Tidskriftsartikel (refereegranskat)abstract
- The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.
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| 4. |
- Augusto, Felipe A., et al.
(författare)
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Mechanism of activated chemiluminescence of cyclic peroxides : 1,2-dioxetanes and 1,2-dioxetanones
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:5, s. 3955-3962
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Tidskriftsartikel (refereegranskat)abstract
- Almost all chemiluminescent and bioluminescent reactions involve cyclic peroxides. The structure of the peroxide and reaction conditions determine the quantum efficiency of light emission. Oxidizable fluorophores, the so-called activators, react with 1,2-dioxetanones promoting the former to their first singlet excited state. This transformation is inefficient and does not occur with 1,2-dioxetanes; however, they have been used as models for the efficient firefly bioluminescence. In this work, we use the SA-CASSCF/CASPT2 method to investigate the activated chemiexcitation of the parent 1,2-dioxetane and 1,2-dioxetanone. Our findings suggest that ground state decomposition of the peroxide competes efficiently with the chemiexcitation pathway, in agreement with the available experimental data. The formation of non-emissive triplet excited species is proposed to explain the low emission efficiency of the activated decomposition of 1,2-dioxetanone. Chemiexcitation is rationalized considering a peroxide/activator supermolecule undergoing an electron-transfer reaction followed by internal conversion.
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| 5. |
- Chen, Shu-Feng, et al.
(författare)
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Chemiluminescence of Coelenterazine and Fluorescence of Coelenteramide : A Systematic Theoretical Study
- 2012
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 8:8, s. 2796-2807
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Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the structural and spectroscopic properties of coelenteramide has been performed at the TD-CAM-B3LYP/6-31+G(d,p) level of theory, including various fluorescence and chemiluminescence states. The influence of geometric conformations, solvent polarity, protonation state, and the covalent character of the O-H bond of the hydroxyphenyl moiety were carefully studied. Striking differences in geometries and electronic structures among the states responsible for light emission were characterized. All fluorescence states can be described as a limited charge transfer process for a planar amide moiety. However, the chemiluminescence state is characterized by a much larger charge transfer that takes place over a longer distance. Moreover, the chemiluminescent coelenteramide structure exhibits an amide moiety that is no longer planar, in agreement with recent, more accurate ab initio results [Roca-Sanjuan et al J. Chem. Theory Comput. 2011, 7, 4060] Because the chemiluminescence state appears to be completely dark, a new mechanism is tentatively introduced for this process.
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| 6. |
- El-Zohry, Ahmed M., et al.
(författare)
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Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes : Experimental and Theoretical Studies
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:5, s. 2249-2259
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Tidskriftsartikel (refereegranskat)abstract
- Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twisting process is assumed to occur as a deactivation process for the excited molecule. This is confirmed by multireference second-order perturbation theory (CASSCF/CASPT2) calculations of the lowest-lying excited state, in which it is shown that torsion of the ethylene bond to 96° and pyramidalization to ca. 100° lead to a conical intersection with the ground state. Embedded in a plastic matrix, where double bond rotation is hindered, the decay is slowed down to nanoseconds. We have also investigated the dyes D102, D131, and D149, possessing the same indoline donor unit, by femtosecond transient absorption and found a similar decay component. The ca. 20 ps deactivation channel in D-family dyes is thus attributed to a twisting process of the donor unit. The fluorescence quantum yields of this unit and D149 were measured, and from comparison, the competition of the discovered twisting deactivation channel to the radiative decay of the excited indoline dyes could be confirmed. Blocking this deactivation channel is expected to further increase efficiency for the indoline dyes.
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| 7. |
- Farahani, Pooria, 1985-, et al.
(författare)
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A Two-Scale Approach to Electron Correlation in Multiconfigurational Perturbation Theory
- 2014
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Ingår i: Journal of Computational Chemistry. - : John Wiley & Sons. - 0192-8651 .- 1096-987X. ; 35:22, s. 1609-1617
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Forskningsöversikt (refereegranskat)abstract
- We present a new approach for the calculation of dynamicelectron correlation effects in large molecular systems usingmulticonfigurational second-order perturbation theory(CASPT2). The method is restricted to cases where partitioningof the molecular system into an active site and an environment is meaningful. Only dynamic correlation effects derivedfrom orbitals extending over the active site are included at theCASPT2 level of theory, whereas the correlation effects of theenvironment are retrieved at lower computational costs. Forsufficiently large systems, the small errors introduced by thisapproximation are contrasted by the substantial savings inboth storage and computational demands compared to thefull CASPT2 calculation. Provided that static correlation effectsare correctly taken into account for the whole system, the proposed scheme represent a hierarchical approach to the electron correlation problem, where two molecular scales aretreated each by means of the most suitable level of theory.
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| 8. |
- Farahani, Pooria, 1985-, et al.
(författare)
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Advances in computationalphotochemistry and chemiluminescenceof biological and nanotechnologicalmolecules
- 2017. - 44
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Ingår i: Photochemistry. - Cambridge, UK : Royal Society of Chemistry. - 1465-1947. ; , s. 16-60, s. 16-60
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Bokkapitel (refereegranskat)abstract
- Recent advances (2014–2015) in computational photochemistry and chemiluminescencederive from the development of theory and from the application of state-of-the-art andnew methodology to challenging electronic-structure problems. Method developmentshave mainly focused, first, on the improvement of approximate and cheap methods toprovide a better description of non-adiabatic processes, second, on the modification ofaccurate methods in order to decrease the computation time and, finally, on dynamicsapproaches able to provide information that can be directly compared with experimentaldata, such as yields and lifetimes. Applications of the ab initio quantum-chemistry methodshave given rise to relevant findings in distinct fields of the excited-state chemistry.We brieflysummarise, in this chapter, the achievements on photochemical mechanisms andchemically-induced excited-state phenomena of interest in biology and nanotechnology.
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| 9. |
- Farahani, Pooria, 1985-, et al.
(författare)
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Revisiting the Nonadiabatic Process in 1,2-Dioxetane
- 2013
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 9:12, s. 5404-5411
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Tidskriftsartikel (refereegranskat)abstract
- Determining the ground and excited-statedecomposition mechanisms of 1,2-dioxetane is essential tounderstand the chemiluminescence and bioluminescencephenomena. Several experimental and theoretical studies hasbeen performed in the past without reaching a converged description. The reason is in part associated with the complex nonadiabatic process taking place along the reaction. The present study is an extension of a previous work (De Vico, L.;Liu, Y.-J.; Krogh, J. W.; Lindh, R. J. Phys. Chem. A 2007, 111,8013−8019) in which a two-step mechanism was established for the chemiluminescence involving asynchronous O−O′ andC−C′ bond dissociations. New high-level multistate multiconfigurational reference second-order perturbation theory calculations and ab initio molecular dynamics simulations at constant temperature are performed in the present study, which provide further details on the mechanisms and allow to rationalize further experimental observations. In particular, the new results explain the high ratio of triplet to singlet dissociation products.
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| 10. |
- Farahani, Pooria, 1985-, et al.
(författare)
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Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane
- 2015
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 17, s. 18653-18664
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Tidskriftsartikel (refereegranskat)abstract
- Excited-state chemistry is usually ascribed to photo-induced processes, such as fluorescence, phosphorescence, and photochemistry, or to bio-and chemiluminescence, in which light emission originates from a chemical reaction. A third class of excited-state chemistry is, however, possible. It corresponds to the photochemical phenomena produced by chemienergizing certain chemical groups without light - chemiexcitation. By studying Dewar dioxetane, which can be viewed as the combination of 1,2-dioxetane and 1,3-butadiene, we show here how the photo-isomerization channel of 1,3-butadiene can be reached at a later stage after the thermal decomposition of the dioxetane moiety. Multi-reference multiconfigurational quantum chemistry methods and accurate reaction-path computational strategies were used to determine the reaction coordinate of three successive processes: decomposition of the dioxetane moiety, non-adiabatic energy transfer from the ground to the excited state, and finally non-radiative decay of the 1,3-butadiene group. With the present study, we open a new area of research within computational photochemistry to study chemically-induced excited-state chemistry that is difficult to tackle experimentally due to the short-lived character of the species involved in the process. The findings shall be of relevance to unveil "dark'' photochemistry mechanisms, which might operate in biological systems under conditions of lack of light. These mechanisms might allow reactions that are typical of photo-induced phenomena.
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