scholarly journals Observation of Enhanced Dissociative Photochemistry in the Non-Native Nucleobase 2-Thiouracil

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3157
Author(s):  
Kelechi O. Uleanya ◽  
Rosaria Cercola ◽  
Maria Nikolova ◽  
Edward Matthews ◽  
Natalie G. K. Wong ◽  
...  
Keyword(s):  
Excited States ◽  
Ground State ◽  
Internal Conversion ◽  
Photophysical Properties ◽  
Ionization Mass ◽  
Deprotonated Form ◽  
Fragment Ions ◽  
Protonated Forms ◽  
Electron Ejection ◽  
Triplet Excited States

We present the first study to measure the dissociative photochemistry of 2-thiouracil (2-TU), an important nucleobase analogue with applications in molecular biology and pharmacology. Laser photodissociation spectroscopy is applied to the deprotonated and protonated forms of 2-TU, which are produced in the gas-phase using electrospray ionization mass spectrometry. Our results show that the deprotonated form of 2-thiouracil ([2-TU-H]−) decays predominantly by electron ejection and hence concomitant production of the [2-TU-H]· free-radical species, following photoexcitation across the UVA-UVC region. Thiocyanate (SCN−) and a m/z 93 fragment ion are also observed as photodecay products of [2-TU-H]− but at very low intensities. Photoexcitation of protonated 2-thiouracil ([2-TU·H]+) across the same UVA-UVC spectral region produces the m/z 96 cationic fragment as the major photofragment. This ion corresponds to ejection of an HS· radical from the precursor ion and is determined to be a product of direct excited state decay. Fragment ions associated with decay of the hot ground state (i.e., the ions we would expect to observe if 2-thiouracil was behaving like UV-dissipating uracil) are observed as much more minor products. This behaviour is consistent with enhanced intersystem crossing to triplet excited states compared to internal conversion back to the ground state. These are the first experiments to probe the effect of protonation/deprotonation on thionucleobase photochemistry, and hence explore the effect of pH at a molecular level on their photophysical properties.

Energies and Dipole Moments of Excited States of Ozone and Ozone Radical Cation Using Fock Space Multireference Coupled-Cluster Analytical Response Approach

2003 ◽  
Vol 68 (1) ◽  
pp. 47-60 ◽  
Author(s):  
Devarajan Ajitha ◽  
Kimihiko Hirao ◽  
Sourav Pal
Keyword(s):  
Excited States ◽  
Radical Cation ◽  
Ground State ◽  
Fock Space ◽  
Dipole Moments ◽  
Cation Radical ◽  
Coupled Cluster ◽  
Complete Active Space ◽  
Triplet Excited States ◽  
Ground State Geometry

Using the Fock space multireference coupled-cluster (FS-MRCC) analytical linear response approach, we report the dipole moments of low-lying singlet and triplet excited states of ozone. The low-lying singlet and triplet excited states are calculated at the ground-state geometry and at the adiabatic geometry for the 1A2 and 1B1. For comparison we also calculate at the ground-state geometry the dipole moments of the 1A2, 1B1 and 1B2 using multireference configuration interaction (MRCI) with a bigger VQZ basis and complete active space. We also report as by-product the excitation energy values in the singles and doubles approximation. At the ground-state geometry we also report the energy and the dipole moments of the 2A1, 2A2 and 2B1 states of the ozone radical cation. The energy of the ozone cation radical is compared with the other correlated approaches. It matches well with the experimental values.

scholarly journals Photochemical processes induced by the irradiation of 4-hydroxybenzophenone in different solvents

2015 ◽  
Vol 14 (11) ◽  
pp. 2087-2096 ◽  
Author(s):  
Francesco Barsotti ◽  
Marcello Brigante ◽  
Mohamed Sarakha ◽  
Valter Maurino ◽  
Claudio Minero ◽  
...  
Keyword(s):  
Fluorescence Quenching ◽  
Excited States ◽  
Ground State ◽  
Photochemical Processes ◽  
Triplet Excited States

The singlet and triplet excited states of 4-hydroxybenzophenone (4BPOH) undergo deprotonation in the presence of water to produce the anionic ground-state, causing fluorescence quenching and photoactivity inhibition.

scholarly journals On Anomalous Fluorescence of Symmetrical Polymethine Dyes

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
P. O. Kondratenko ◽  
Yu. M. Lopatkin
Keyword(s):  
Excited States ◽  
Ground State ◽  
Internal Conversion ◽  
Polymethine Dyes ◽  
Necessary Condition ◽  
Relaxation Processes ◽  
Sufficient Condition ◽  
Radiative Relaxation ◽  
Higher Excited States ◽  
Group Theoretical Analysis

The group-theoretical analysis of polymethine dyes (PMD) showed that relaxation processes between the states S3 and S1 are forbidden, either by radiation or by internal conversion. From the state S3, only transition to the ground state of the molecule is possible. Since the experimental data state that the quantum yield of S3 ⟶ S0 fluorescence does not exceed 1%, it is indicated that the internal conversion rate can be 2 orders of magnitude higher than the radiative relaxation rate of the molecule. Concerning the reasons for the appearance of fluorescence from the higher excited states of molecules, it can be asserted that the necessary condition for the appearance of S3 ⟶ S0 fluorescence is the absence of S0 ⟶ S1(v)-absorption in the region of the S0 ⟶ S3 transition. The sufficient condition is the corresponding symmetry of the excited states, which imposes a prohibition on the S3 ⟶ S1 relaxation process.

scholarly journals Structure-Reactivity Correlations of Excited States of Perfluorinated Compounds: A Time Resolved Raman Study

1999 ◽  
Vol 19 (1-4) ◽  
pp. 343-348 ◽  
Author(s):  
R. Anandhi ◽  
G. Balakrishnan ◽  
P. Mohandas ◽  
S. Umapathy
Keyword(s):  
Excited States ◽  
Ground State ◽  
Perfluorinated Compounds ◽  
Spectral Studies ◽  
Triplet Excited State ◽  
Time Resolved ◽  
Organic Systems ◽  
Structural Distortions ◽  
Raman Study ◽  
Triplet Excited States

This paper reports the TR3 spectral studies on perfluorinated organic systems with the objective to understand the influence of perfluorination on the excited states. We have recorded the TR3 spectra and Raman excitation profiles of the triplet excited states of decafluorobenzophenone and fluoranil. It is found that the influence of perfluorination is more pronounced in the triplet excited state than the ground state and thus leads to enhanced reactivity for perfluorinated compounds through larger structural distortions.

Synthesis and photophysical properties of covalent conjugates of aqua platinum(II) and octacarboxy-substituted zinc phthalocyanine

2012 ◽  
Vol 16 (11) ◽  
pp. 1217-1224 ◽  
Author(s):  
Roman A. Bulgakov ◽  
Nina A. Kuznetsova ◽  
Olga V. Dolotova ◽  
Ludmila I. Solovieva ◽  
John Mack ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Excited States ◽  
Photophysical Properties ◽  
Zinc Phthalocyanine ◽  
Limited Effect ◽  
Oxygen Formation ◽  
Dual Action ◽  
Photochemical Properties ◽  
Triplet Excited States ◽  
Covalent Conjugates

New covalent conjugates of aqua platinum(II) and octacarboxy-substituted zinc phthalocyanine, bearing one, two, three and four aqua platinum moieties on the periphery of the Pc ligand have been synthesized and characterized. The effect of the stepwise introduction of the aqua platinums on the photophysical and photochemical properties of these compounds has been investigated in dimethylsulfoxide solution. It has been found that aqua platinum moieties have only a limited effect on the dynamics of the singlet and triplet excited states, on the ability to sensitize singlet oxygen formation and on the photostability. Each conjugate has a high singlet oxygen quantum yield (ΦΔ 0.51–0.62) and thus retains potential for use as a dual action anticancer drugs by acting as a sensitizer for PDT in addition to the likely chemotherapeutic effects of the Pt(II) complexes.

Low-Lying Positive-Parity States in 101Tc

1972 ◽  
Vol 50 (13) ◽  
pp. 1511-1517 ◽  
Author(s):  
W. B. Cook ◽  
M. W. Johns ◽  
J. S. Geiger ◽  
R. L. Graham
Keyword(s):  
Excited States ◽  
Ground State ◽  
Decay Scheme ◽  
Internal Conversion ◽  
Conversion Coefficient ◽  
Low Energy ◽  
Positive Parity ◽  
Β Decay ◽  
Energy Transitions ◽  
Conversion Measurement

Internal conversion measurement studies of the 14.6 min 101Mo β decay have led to the discovery of the following low-energy transitions in 101Tc: 6.281 ± 0.007 (75.4 ± 9%), 9.317 ± 0.010 (97 ± 1%), and 15.606 ± 0.015 keV (1.9 + 0.3%). From relative L-subshell intensities, the 6.281 and 9.317 keV transitions are found to be M1 with E2 admixtures of 0.010 ± 0.005% and 0.021 + 0.006% respectively; the weak 15.606 keV transition is E2 in character. These transitions establish excited states in 101Tc at 9.317 ± 0.010 and 15.601 ± 0.009 keV. The measured multipolarities together with decay scheme considerations lead to Jπ values of 9/2 +, 7/2 +, and 5/2 + for the ground state, the 9.317, and the 15.601 keV states respectively. Since these transitions were not observed in earlier studies of the β decay of 101Mo, quoted decay energies have been 15.6 keV too low. The measured K-conversion coefficient of the 80.926 keV transition shows that it is M1 with an E2 component of < 9%.

Solvent Dependence of Structural Dynamics and Spin-flip Processes in 3,4,5-tri(9H-carbazole-9-yl)benzonitrile (ortho-3CzBN)

2020 ◽  
Author(s):  
Masaki Saigo ◽  
Kiyoshi Miyata ◽  
Hajime Nakanotani ◽  
Chihaya Adachi ◽  
Ken Onda
Keyword(s):  
Dft Calculations ◽  
Excited States ◽  
Structural Changes ◽  
Photophysical Properties ◽  
Delayed Fluorescence ◽  
Time Resolved ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Solvent Dependence ◽  
Acetonitrile Solutions

We have investigated the solvent-dependence of structural changes along with intersystem crossing of a thermally activated delayed fluorescence (TADF) molecule, 3,4,5-tri(9H-carbazole-9-yl)benzonitrile (o-3CzBN), in toluene, tetrahydrofuran, and acetonitrile solutions using time-resolved infrared (TR-IR) spectroscopy and DFT calculations. We found that the geometries of the S1 and T1 states are very similar in all solvents though the photophysical properties mostly depend on the solvent. In addition, the time-dependent DFT calculations based on these geometries suggested that the thermally activated delayed fluorescence process of o-3CzBN is governed more by the higher-lying excited states than by the structural changes in the excited states.<br>

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