| 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. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Francés-Monerris, Antonio, et al.
(författare)
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Triplet versus singlet chemiexcitation mechanism in dioxetanone : a CASSCF/CASPT2 study
- 2017
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 136:6
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Tidskriftsartikel (refereegranskat)abstract
- Chemiluminescence is a fundamental process of chemistry consisting in the conversion of chemical energy stored in chemical bonds into light. It is used by nature and by man-made technology, being especially relevant in chemical analysis. The understanding of the phenomenon strongly relies in the study of peroxide models such as 1,2-dioxetanones. In the present contribution, the singlet S2 and the triplet T2 potential energy surfaces of the unimolecular decomposition of 1,2-dioxetanone have been mapped along the O-O and C-C bond coordinates on the grounds of the multiconfigurational CASPT2//CASSCF approach. Results confirm the energy degeneracy between T2, T1, S1, and S0 at the TS region, whereas S2 is unambiguously predicted at higher energies. Triplet-state population is also supported by the spin-orbit couplings between the singlet and triplet states partaking in the process. In particular, the first-principle calculations show that decomposition along the T2 state is a competitive process, having a small (similar to 3 kcal/mol) energy barrier from the ground-state TS structure. The present findings can explain the higher quantum yield of triplet-state population with respect to the excited singlet states recorded experimentally for the uni-molecular decomposition of 1,2-dioxetanone models.
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| 8. |
- Lindh, Roland, 1958-, et al.
(författare)
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Recent method developments and applications in computational photochemistry, chemiluminescene and bioluminescence
- 2015. - 42
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Ingår i: <em>Photochemistry: Volume 42</em>. - Cambridge : Royal Society of Chemistry. - 9781849739566 - 9781782624547 - 9781782623038 ; , s. 11-42
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This review summarises and discusses the advances of computational photochemistry in 2012 and 2013 in both methodology and applications fields. The methodological developments of models and tools used to study and simulate non-adiabatic processes are highlighted. These developments can be summarised as assessment studies, new methods to locate conical intersections, tools for representation, interpretation and visualisation, new computational approaches and studies introducing simpler models to rationalise the quantum dynamics near and in the conical intersection. The applied works on the topics of photodissociation, photostability, photoisomerisations, proton/charge transfer, chemiluminescence and bioluminescence are summarised, and some illustrative examples of studies are analysed in more detail, particularly with reference to photostability and chemi/bioluminescence. In addition, theoretical studies analysing solvent effects are also considered. We finish this review with conclusions and an outlook on the future.
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| 9. |
- Marazzi, Marco, et al.
(författare)
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Benzophenone Ultrafast Triplet Population : Revisiting the Kinetic Model by Surface-Hopping Dynamics
- 2016
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 7:4, s. 622-626
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Tidskriftsartikel (refereegranskat)abstract
- The photochemistry of benzophenone, a paradigmatic organic molecule for photosensitization, was investigated by means of surface-hopping ab initio molecular dynamics. Different mechanisms were found to be relevant within the first 600 fs after excitation; the long debated direct (S-1 -> T-1) and indirect (S-1 -> T-2 -> T-1) mechanisms for population of the low-lying triplet state are both possible, with the latter being prevalent. Moreover, we established the existence of a kinetic equilibrium between the two triplet states, never observed before. This fact implies that a significant fraction of the overall population resides in T-2, eventually allowing one to revisit the usual spectroscopic assignment proposed by transient absorption spectroscopy. This finding is of particular interest for photocatalysis as well as for DNA damages studies because both T-1 and T-2 channels are, in principle, available for benzophenone-mediated photoinduced energy transfer toward DNA.
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| 10. |
- Schapiro, Igor, et al.
(författare)
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A surface hopping algorithm for nonadiabatic minimum energy path calculations
- 2015
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Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 36:5, s. 312-20
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Tidskriftsartikel (refereegranskat)abstract
- The article introduces a robust algorithm for the computation of minimum energy paths transiting along regions of near-to or degeneracy of adiabatic states. The method facilitates studies of excited state reactivity involving weakly avoided crossings and conical intersections. Based on the analysis of the change in the multiconfigurational wave function the algorithm takes the decision whether the optimization should continue following the same electronic state or switch to a different state. This algorithm helps to overcome convergence difficulties near degeneracies. The implementation in the MOLCAS quantum chemistry package is discussed. To demonstrate the utility of the proposed procedure four examples of application are provided: thymine, asulam, 1,2-dioxetane, and a three-double-bond model of the 11-cis-retinal protonated Schiff base.
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