An electron paramagnetic resonance study of the excited triplet states of adenine and some of its derivatives in aqueous glasses at 77 K

Arce, Rafael; Rodríguez, G.

doi:10.1016/0047-2670(86)87022-8

Cited by 10 publications

(4 citation statements)

References 26 publications

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“…Currently, there is a consensus that the triplet states are responsible of the longest component of the multiexponential decay of monobases. It is well known experimentally that long-time signals are quenched in the presence of oxygen, yielding high yields in aprotic solvents [327,328] Yet, several experimental evidences need rationalization, like for example, the larger quantum yields of phosphorescence than of fluorescence in monobases, [329] the prevalence of A and T signals of DNA at lower temperatures [330][331][332] or the observed wavelength dependence of the triplet state formation. [333] To shed some light into these phenomena, the theoretical elucidation of the ISC channels is of great importance.…”

Section: Photochemistry Of Dna/rna Constituentsmentioning

confidence: 99%

Progress and Challenges in the Calculation of Electronic Excited States

2011

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A detailed understanding of the properties of electronic excited states and the reaction mechanisms that molecules undergo after light irradiation is a fundamental ingredient for following light-driven natural processes and for designing novel photonic materials. The aim of this review is to present an overview of the ab initio quantum chemical and time-dependent density functional theory methods that can be used to model spectroscopy and photochemistry in molecular systems. The applicability and limitations of the different methods as well as the main frontiers are discussed. To illustrate the progress achieved by excited-state chemistry in the recent years as well as the main challenges facing computational chemistry, three main applications that reflect the authors' experience are addressed: the UV/Vis spectroscopy of organic molecules, the assignment of absorption and emission bands of organometallic complexes, and finally, the obtainment of non-adiabatic photoinduced pathways mediated by conical intersections. In the latter case, special emphasis is put on the photochemistry of DNA. These applications show that the description of electronically excited states is a rewarding but challenging area of research.

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Section: Photochemistry Of Dna/rna Constituentsmentioning

confidence: 99%

Progress and Challenges in the Calculation of Electronic Excited States

2011

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“…Participation of triplet excited states is at focus in many modern studies of biochemical processes like photodynamic therapy, vision, respiration, photochemistry of DNA components, peptides and retinals. The low-temperature phosphorescence spectra of DNA are shown to consist of two basic bands originating predominantly from the thymine and adenine bases. , The prevalence of these two molecules and the absence of triplet guanine signals have not been explained until recent time . The involvement of triplet states in the fast energy deactivation and vibrational relaxation processes for the pyrimidine-type DNA nucleobase components have been elucidated quite precisely by Marian , and Marquetand both theoretically and experimentally, but further future studies are certainly needed (in particular for the thymine nucleobase).…”

Section: Some Recent Applications Of Singlet-triplet Transitionsmentioning

confidence: 99%

Theory and Calculation of the Phosphorescence Phenomenon

2017

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Phosphorescence is a phenomenon of delayed luminescence that corresponds to the radiative decay of the molecular triplet state. As a general property of molecules, phosphorescence represents a cornerstone problem of chemical physics due to the spin prohibition of the underlying triplet-singlet emission and because its analysis embraces a deep knowledge of electronic molecular structure. Phosphorescence is the simplest physical process which provides an example of spin-forbidden transformation with a characteristic spin selectivity and magnetic field dependence, being the model also for more complicated chemical reactions and for spin catalysis applications. The bridging of the spin prohibition in phosphorescence is commonly analyzed by perturbation theory, which considers the intensity borrowing from spin-allowed electronic transitions. In this review, we highlight the basic theoretical principles and computational aspects for the estimation of various phosphorescence parameters, like intensity, radiative rate constant, lifetime, polarization, zero-field splitting, and spin sublevel population. Qualitative aspects of the phosphorescence phenomenon are discussed in terms of concepts like structure-activity relationships, donor-acceptor interactions, vibronic activity, and the role of spin-orbit coupling under charge-transfer perturbations. We illustrate the theory and principles of computational phosphorescence by highlighting studies of classical examples like molecular nitrogen and oxygen, benzene, naphthalene and their azaderivatives, porphyrins, as well as by reviewing current research on systems like electrophosphorescent transition metal complexes, nucleobases, and amino acids. We furthermore discuss modern studies of phosphorescence that cover topics of applied relevance, like the design of novel photofunctional materials for organic light-emitting diodes (OLEDs), photovoltaic cells, chemical sensors, and bioimaging.

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“…Indeed, 5-formylcytosine (5fC), which is also an intermediate during demethylation of the cytosine base in DNA, has been recently demonstrated to be a photosensitizer in DNA. 52 Although the measured 27% triplet quantum yield in f 6 A at room temperature is lower than that seen in 5fC (∼69%), 22 it is two orders of magnitude higher than the triplet yield of adenosine at 77 K. 53 Unfortunately, the triplet yield of hm 6 A cannot be measured, because the formation of its triplet is not complete within the limit of our experimental time window (∼1 ns). However, the yield could be at the same level as that in f 6 A because of a similar ns-TA signal strength.…”

Section: Discussionmentioning

confidence: 68%

“…64,65 The ISC mechanism in f 6 A is similar to those proposed in pyrimidines, but the triplet quantum yield of f 6 A at room temperature is at least one order of magnitude higher than those reported in pyrimidines and it is two orders of magnitude higher than that in adenosine at 77K. 53 This suggests that f 6 A may act as an intrinsic damage trigger in RNA during the demethylation process, which could lead to further mutations and diseases. 19…”

Section: Discussionmentioning

confidence: 86%