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1.
The Triplet State of 6‐thio‐2′‐deoxyguanosine: Intrinsic Properties and Reactivity Toward Molecular Oxygen 下载免费PDF全文
Marvin Pollum Steffen Jockusch Carlos E. Crespo‐Hernández 《Photochemistry and photobiology》2016,92(2):286-292
Thiopurine prodrugs are currently among the leading treatment options for leukemia, immunosuppression, and arthritis. Patients undergoing long‐term thiopurine treatment are at a higher risk of developing sunlight‐induced skin cancers than the general population. This side effect originates from the cellular metabolization of thiopurine prodrugs to form 6‐thio‐2′‐deoxyguanosine, which can absorb UVA radiation, populating its reactive triplet state and leading to oxidatively generated damage. However, the photo‐oxidation mechanism is not fully understood. In this contribution, the oxidation potential and the adiabatic triplet energy of 6‐thio‐2′‐deoxyguanosine are estimated computationally, whereas the intrinsic rate of triple‐state decay and the rate constant for triplet quenching by molecular oxygen are determined using time‐resolved spectroscopic techniques. A singlet oxygen quantum yield of 0.24 ± 0.02 is measured in aqueous solution (0.29 ± 0.02 in acetonitrile). Its magnitude correlates with the relatively low percentage of triplet‐O2 collision events that generate singlet oxygen (SΔ = 37%). This behavior is rationalized as being due to the exergonic driving force for electron transfer between the triplet state of 6‐thio‐2′‐deoxyguanosine and molecular oxygen (ΔGET = ?69.7 kJ mol?1), resulting in the formation of a charge‐transfer complex that favors nonradiative decay to the ground state over triplet energy transfer. 相似文献
2.
Claude Schweitzer Zahra Mehrdad Astrid Noll Erich‐Walter Grabner Reinhard Schmidt 《Helvetica chimica acta》2001,84(9):2493-2507
We have studied the charge‐transfer‐induced deactivation of nπ* excited triplet states of benzophenone derivatives by O2(3Σ), and the charge‐transfer‐induced deactivation of O2(1Δg) by ground‐state benzophenone derivatives in CH2Cl2 and CCl4. The rate constants for both processes are described by Marcus electron‐transfer theory, and are compared with the respective data for a series of biphenyl and naphthalene derivatives, the triplet states of which have ππ* configuration. The results demonstrate that deactivation of the locally excited nπ* triplets occurs by local charge‐transfer and non‐charge‐transfer interactions of the oxygen molecule with the ketone carbonyl group. Relatively large intramolecular reorganization energies show that this quenching process involves large geometry changes in the benzophenone molecule, which are related to favorable Franck‐Condon factors for the deactivation of ketone‐oxygen complexes to the ground‐state molecules. This leads to large rate constants in the triplet channel, which are responsible for the low efficiencies of O2(1Δg) formation observed with nπ* excited ketones. Compared with the deactivation of ππ* triplets, the non‐charge‐transfer process is largely enhanced, and charge‐transfer interactions are less important. The deactivation of singlet oxygen by ground‐state benzophenone derivatives proceeds via interactions of O2(1Δg) with the Ph rings. 相似文献
3.
Dr. Zafar Mahmood Noreen Rehmat Prof. Shaomin Ji Prof. Jianzhang Zhao Shanshan Sun Dr. Mariangela Di Donato Prof. Mingde Li Maria Teddei Prof. Yanping Huo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14912-14918
Zinc(II) bis(dipyrrin) complexes, which feature intense visible absorption and efficient symmetry breaking charge transfer (SBCT) are outstanding candidates for photovoltaics but their short lived triplet states limit applications in several areas. Herein we demonstrate that triplet excited state dynamics of bis(dipyrrin) complexes can be efficiently tuned by attaching electron donating aryl moieties at the 5,5′-position of the complexes. For the first time, a long lived triplet excited state (τT=296 μs) along with efficient ISC ability (ΦΔ=71 %) was observed for zinc(II) bis(dipyrrin) complexes, formed via SBCT. The results revealed that molecular geometry and energy gap between the charge transfer (CT) state and triplet energy levels strongly control the triplet excited state properties of the complexes. An efficient triplet–triplet annihilation upconversion system was devised for the first time using a SBCT architecture as triplet photosensitizer, reaching a high upconversion quantum yield of 6.2 %. Our findings provide a blueprint for the development of triplet photosensitizers based on earth abundant metal complexes with long lived triplet state for revolutionary photochemical applications. 相似文献
4.
Dr. Zhenyi Yu Yishi Wu Qian Peng Chunlin Sun Jianwei Chen Prof. Jiannian Yao Prof. Hongbing Fu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4717-4722
Previous studies of perylenediimides (PDIs) mostly utilized the lowest singlet excited state S1. Generation of a triplet excited state (T1) in PDIs is important for applications ranging from photodynamic therapy to photovoltaics; however, it remains a formidable task. Herein, we developed a heavy‐atom‐free strategy to prompt the T1←S1 intersystem crossing (ISC) by introducing electron‐donating aryl (Ar) groups at the head positions of an electron‐deficient perylenediimide (PDI) core. We found that the ISC efficiency increases from 8 to 54 % and then to 86 % by increasing the electron‐donating ability of head‐substituted aryl groups from phenyl (p‐PDI) to methoxyphenyl (MeO‐PDI) and then to methylthioxyphenyl (MeS‐PDI). By enhancing the intramolecular charge‐transfer (ICT) interaction from p‐PDI to MeO‐PDI, and then to MeS‐PDI, singlet oxygen generation via energy‐transfer reactions from T1 of PDIs to 3O2 was demonstrated with the highest yield of up to 80 %. These results provide guidelines for developing new triplet‐generating PDIs and related rylene diimides for optoelectronic applications. 相似文献
5.
Ling Huang Xiaoneng Cui Prof. Bruno Therrien Prof. Jianzhang Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(51):17472-17482
C60–bodipy triads and tetrads based on the energy‐funneling effect that show broadband absorption in the visible region have been prepared as novel triplet photosensitizers. The new photosensitizers contain two or three different light‐harvesting antennae associated with different absorption wavelengths, resulting in a broad absorption band (450–650 nm). The panchromatic excitation energy harvested by the bodipy moieties is funneled into a spin converter (C60), thus ensuring intersystem crossing and population of the triplet state. Nanosecond time‐resolved transient absorption and spin density analysis indicated that the T1 state is localized on either C60 or the antennae, depending on the T1 energy levels of the two entities. The antenna‐localized T1 state shows a longer lifetime (τT=132.9 μs) than the C60‐localized T1 state (ca. 27.4 μs). We found that the C60 triads and tetrads can be used as dual functional photocatalysts, that is, singlet oxygen (1O2) and superoxide radical anion (O2 . ?) photosensitizers. In the photooxidation of naphthol to juglone, the 1O2 photosensitizing ability of the C60 triad is a factor of 8.9 greater than the conventional triplet photosensitizers tetraphenylporphyrin and methylene blue. The C60 dyads and triads were also used as photocatalysts for O2 . ?‐mediated aerobic oxidation of aromatic boronic acids to produce phenols. The reaction times were greatly reduced compared with when [Ru(bpy)3Cl2] was used as photocatalyst. Our study of triplet photosensitizers has shown that broadband absorption in the visible spectral region and long‐lived triplet excited states can be useful for the design of new heavy‐atom‐free organic triplet photosensitizers and for the application of these triplet photosensitizers in photo‐organocatalysis. 相似文献
6.
Rationally Investigating the Influence of T1 Location on Electroluminescence Performance of Aryl Amine Modified Phosphine Oxide Materials 下载免费PDF全文
Chunmiao Han Liping Zhu Jing Li Fangchao Zhao Dr. Hui Xu Prof. Dongge Ma Prof. Pengfei Yan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16350-16359
The correspondence between triplet location effect and host‐localized triplet–triplet annihilation and triplet–polaron quenching effects was performed on the basis of a series of naphthyldiphenylamine (DPNA)‐modified phosphine oxide hosts. The number and ratio of DPNA and diphenylphosphine oxide was adjusted to afford symmetrical and unsymmetrical molecular structures and different electronic environments. As designed, the first triplet (T1) states were successfully localized on the specific DPNA chromophores. Owing to the meso‐ and multi‐insulating linkages, identical optical properties and comparable electrical performance was observed, including the same first singlet (S1) and T1 energy levels to support the similar singlet and triplet energy transfer and the close frontier molecular orbital energy levels. This established the basis of rational investigation on T1 location effect without interference from other optoelectronic factors. 相似文献
7.
Quenching of triplet states of aromatic hydrocarbons by nitroxyl radicals has been investigated by the flash photolysis method. There are two different mechanisms of triplet quenching: quenching occurs via enhanced intersystem crossing on exchange interaction with the radical for the triplet states of aromatic hydrocarbons which have low triplet energy (ET < 14700 cm?1); for very high triplet energies, energy transfer from the triplet molecule to the nitroxyl radical occurs. The energy of the excited nitroxyl radical was estimated to be 18000 cm?1. 相似文献
8.
Linqing Qin Xingzheng Liu Xin Zhang Jianwei Yu Lei Yang Fenggui Zhao Miaofei Huang Kangwei Wang Xiaoxi Wu Yuhao Li Hao Chen Kai Wang Jianlong Xia Xinhui Lu Feng Gao Yuanping Yi Hui Huang 《Angewandte Chemie (International ed. in English)》2020,59(35):15043-15049
Triplet acceptors have been developed to construct high‐performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T1) are close to those of charge‐transfer states (3CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π‐conjugated core and D‐A structure, were confirmed to be triplet materials, leading to high‐performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D‐A structures result in large spin–orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T1 is close to 3CT, facilitating the split of triplet exciton to free charges. 相似文献
9.
Dr. Xian‐Sheng Ke Yingying Ning Juan Tang Ji‐Yun Hu Hao‐Yan Yin Gao‐Xiang Wang Zi‐Shu Yang Jialong Jie Dr. Kunhui Liu Dr. Zhao‐Sha Meng Zongyao Zhang Prof. Dr. Hongmei Su Prof. Dr. Chunying Shu Prof. Dr. Jun‐Long Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9676-9686
Construction of GdIII photosensitizers is important for designing theranostic agents owing to the unique properties arising from seven unpaired f electrons of the Gd3+ ion. Combining these with the advantages of porpholactones with tunable NIR absorption, we herein report the synthesis of GdIII complexes Gd‐1 – 4 ( 1 , porphyrin; 2 , porpholactone; 3 and 4 , cis‐ and trans‐porphodilactone, respectively) and investigated their function as singlet oxygen (1O2) photosensitizers. These Gd complexes displayed 1O2 quantum yields (ΦΔs) from 0.64–0.99 with the order Gd‐1 < Gd‐2 < Gd‐3 < Gd‐4 . The gradually enhanced 1O2 sensitization after β‐oxazolone moiety replacement was ascribed to the narrowing of the energy gap (ΔE) between the lowest triplet states (T1) of the ligand and the energy level of the 1Δg→3Σg transition of 1O2. In particular, Gd‐4 is capable of excitation in the visible to NIR region (400–700 nm) with a quantum yield near unity. These Gd complexes were first demonstrated as efficient photosensitizers in photocatalysis such as oxidative C?H bond functionalization of secondary or tertiary amines, and the oxygenation of the natural product cholesterol. Finally, after glycosylation, these water‐soluble Gd complexes showed potential applications in photodynamic therapy (PDT) in HeLa cells. This work revealed that GdIII complexes of “bioinspired” β‐modified porpholactones are efficient NIR photosensitizers and form a chemical basis to construct appealing photocatalysts and theranostic agents based on lanthanides. 相似文献
10.
Azusa Kikuchi Nozomi Oguchi‐Fujiyama Kazuyuki Miyazawa Mikio Yagi 《Photochemistry and photobiology》2014,90(3):511-516
The phosphorescence decay of a UV‐A absorber, 4‐tert‐butyl‐4′‐methoxydibenzolymethane (BMDBM) has been observed following a 355 nm laser excitation in the absence and presence of UV‐B absorbers, 2‐ethylhexyl 4‐methoxycinnamate (octyl methoxycinnamate, OMC) and octocrylene (OCR) in ethanol at 77 K. The lifetime of the lowest excited triplet (T1) state of BMDBM is significantly reduced in the presence of OMC and OCR. The observed quenching of BMDBM triplet by OMC and OCR suggests that the intermolecular triplet–triplet energy transfer occurs from BMDBM to OMC and OCR. The T1 state of OCR is nonphosphorescent or very weakly phosphorescent. However, we have shown that the energy level of the T1 state of OCR is lower than that of the enol form of BMDBM. Our methodology of energy‐donor phosphorescence decay measurements can be applied to the study of the triplet–triplet energy transfer between UV absorbers even if the energy acceptor is nonphosphorescent. In addition, the delayed fluorescence of BMDBM due to triplet–triplet annihilation was observed in the BMDBM–OMC and BMDBM–OCR mixtures in ethanol at 77 K. Delayed fluorescence is one of the deactivation processes of the excited states of BMDBM under our experimental conditions. 相似文献
11.
Tom Polívka 《Photochemistry and photobiology》2019,95(1):453-454
Mimicking light‐harvesting and photoprotective processes of natural photosynthesis by artificial supramolecular systems is of considerable interest for artificial photosynthesis. The authors of the highlighted paper report on synthesis and spectroscopic characterization of a novel Pd‐phthalocyanine–carotenoid dyads that allow to directly follow the triplet–triplet energy transfer between Pd‐phthalocyanine and carotenoid. Unexpectedly, the T‐T energy transfer does not follow the dependence on conjugation length of the acceptor carotenoid. Instead, the donor–acceptor coupling and resulting T‐T energy transfer rate is controlled by the presence or absence of a methyl groups on the conjugated chain in the vicinity of the carotenoid keto‐oxygen. This reveals yet another level of tuning the spectroscopic properties of carotenoids having a conjugated keto group in their structure, underlining their potential for tailoring specific supramolecular complexes carrying out either light‐harvesting or photoprotective functions. 相似文献
12.
AymanA. Abdel‐Shafi PaulD. Beer RogerJ. Mortimer Francis Wilkinson 《Helvetica chimica acta》2001,84(9):2784-2795
Photophysical properties in dilute MeCN solution are reported for seven RuII complexes containing two 2,2′‐bipyridine (bpy) ligands and different third ligands, six of which contain a variety of 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridines, for one complex containing no 2,2′‐bipyridine, but 2 of these different ligands, for three multinuclear RuII complexes containing 2 or 4 [Ru(bpy)2] moieties and also coordinated via 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridine ligands, and for the complex [(Ru(bpy)2(L)]2+ where L is N,N′‐([2,2′‐bipyridine]‐4,4′‐diyl)bis[3‐methoxypropanamide]. Absorption maxima are red‐shifted with respect to [Ru(bpy)3]2+, as are phosphorescence maxima which vary from 622 to 656 nm. The lifetimes of the lowest excited triplet metal‐to‐ligand charge transfer states 3MLCT in de‐aerated MeCN are equal to or longer than for [Ru(bpy)3]2+ and vary considerably, i.e., from 0.86 to 1.71 μs. Rate constants kq for quenching by O2 of the 3MLCT states were measured and found to be well below diffusion‐controlled, ranging from 1.2 to 2.0⋅109 dm3 mol−1 s−1. The efficiencies f of singlet‐oxygen formation during oxygen quenching of these 3MLCT states are relatively high, namely 0.53 – 0.89. The product of kq and f gives the net rate constant k for quenching due to energy transfer to produce singlet oxygen, and kq−k equals k, the net rate constant for quenching due to energy dissipation of the excited 3MLCT states without energy transfer. The quenching rate constants were both found to correlate with ΔGCT, the free‐energy change for charge transfer from the excited Ru complex to oxygen, and the relative and absolute values of these rate constants are discussed. 相似文献
13.
Marta E. Alberto Gloria Mazzone Angelo D. Quartarolo Flavio Fortes Ramos Sousa Emilia Sicilia Nino Russo 《Journal of computational chemistry》2014,35(29):2107-2113
The main photophysical properties of a series of recently synthetized 1,2‐ and 1,3‐squaraines, including absorption electronic spectra, singlet‐triplet energy gaps, and spin‐orbit matrix elements, have been investigated by means of density functional theory (DFT) and time‐dependent DFT approaches. A benchmark of three exchange‐correlation functionals has been performed in six different solvent environments. The investigated 1,2 squaraines have been found to possess two excited triplet states (T1 and T2) that lie below the energy of the excited singlet one (S1). The radiationless intersystem spin crossing efficiency is thus enhanced in both the studied systems and both the transitions could contribute to the excited singlet oxygen production. Moreover, they have a singlet‐triplet energy gap higher than that required to generate the cytotoxic singlet oxygen species. According to our data, these compounds could be used in photodynamic therapy applications that do not require high tissue penetration. © 2014 Wiley Periodicals, Inc. 相似文献
14.
Theoretical study on photooxidation mechanism of ruthenium complex [Ru(II)‐(bpy)2(TMBiimH2)]2+ with molecular oxygen 下载免费PDF全文
Li‐Hong Liu Dan Wu Shu‐Hua Xia Ganglong Cui 《Journal of computational chemistry》2016,37(24):2212-2219
Photoinduced reactions of ruthenium complexes with molecular oxygen have attracted a lot of experimental attention; however, the reaction mechanism remains elusive. In this work, we have used the density functional theory method to scrutinize the visible‐light induced photooxidation mechanism of the ruthenium complex [Ru(II)‐(bpy)2(TMBiimH2)]2+ (bpy: 2, 2‐bipyridine and TMBiimH2: 4, 5, 4, 5‐tetramethyl‐2, 2‐biimidazole) initiated by the attack of molecular oxygen. The present computational results not only explain very well recent experiments, also provide new mechanistic insights. We found that: (1) the triplet energy transfer process between the triplet molecular oxygen and the metal‐ligand charge transfer triplet state of the ruthenium complex, which leads to singlet molecular oxygen, is thermodynamically favorable; (2) the singlet oxygen addition process to the S0 ruthenium complex is facile in energy; (3) the chemical transformation from endoperoxide to epidioxetane intermediates can be either two‐ or one‐step reaction (the latter is energetically favored). These findings contribute important mechanistic information to photooxidation reactions of ruthenium complexes with molecular oxygen. © 2016 Wiley Periodicals, Inc. 相似文献
15.
《Photochemistry and photobiology》2018,94(5):865-874
The photophysical behavior of two xanthene dyes, Eosin Y and Phloxine B, included in microcrystalline cellulose particles is studied in a wide concentration range, with emphasis on the effect of dye concentration on fluorescence and triplet quantum yields. Absolute fluorescence quantum yields in the solid‐state were determined by means of diffuse reflectance and steady‐state fluorescence measurements, whereas absolute triplet quantum yields were obtained by laser‐induced optoacoustic spectroscopy and their dependence on dye concentration was confirmed by diffuse reflectance laser flash photolysis and time‐resolved phosphorescence measurements. When both quantum yields are corrected for reabsorption and reemission of radiation, Φ F values decrease strongly on increasing dye concentration, while a less pronounced decay is observed for Φ T. Fluorescence concentration quenching is attributed to the formation of dye aggregates or virtual traps resulting from molecular crowding. Dimeric traps are however able to generate triplet states. A mechanism based on the intermediacy of charge‐transfer states is proposed and discussed. Calculation of parameters for photoinduced electron transfer between dye molecules within the traps evidences the feasibility of the proposed mechanism. Results demonstrate that photoactive energy traps, capable of yielding dye triplet states, can be formed even in highly‐concentrated systems with random dye distributions. 相似文献
16.
《Chemphyschem》2004,5(1):57-67
Excitation‐energy transport (EET) phenomena in meso–meso directly linked Zn(II )porphyrin arrays in the singlet and triplet excited states were investigated with a view to electronic coupling strength and coherence length by steady‐state and time‐resolved spectroscopic measurements. To investigate energy transfer in the triplet states, we modified the Zn(II )porphyrin arrays with bromo substituents at both ends. The coupling strength of the Soret bands of the arrays was estimated to be about 2200 cm?1, and that of the Q bands is about 570 cm?1. The coherence length in the S1 state of the Zn(II )porphyrin arrays was determined to be 4–5 porphyrin units, which is comparable to that of the well‐ordered two‐dimensional circular structure B850 in the peripheral light‐harvesting antenna (LH2) in photosynthetic purple bacteria. This indicates that the Zn(II )porphyrin arrays are well suited for mimicking natural light‐harvesting antenna complexes. On the other hand, the rate of energy transfer in the triplet state is estimated to be on the order of 100 μs?1, and the very weak coupling between the triplet states (ca. 0.003 cm?1), indicates that the triplet excitation energy is essentially localized on a single porphyrin moiety. 相似文献
17.
F. Elisei G. G. Aloisi F. Dall'Acqua L. Latterini F. Masetti P. Rodighiero 《Photochemistry and photobiology》1998,68(2):164-172
The decay processes of the lowest excited singlet and triplet states of five methylated angelicins (4,6,4′-trimethyl-angelicin, MA, and four methylated thioangelicins, MTA; see Scheme 1) were investigated in live solvents by stationary and pulsed fluorometric and flash photolytic techniques. In particular, the solvent effects on absorption, fluorescence, quantum yields of fluorescence (φF) and triplet formation (φT), lifetimes of fluorescence (τF) and the triplet state (τT) and the quantum yields of singlet oxygen production (φΔ) were investigated. Semiempirical (ZINDO/S-CI) calculations were carried out to obtain information (transition probabilities and nature) on the lowest excited singlet and triplet states. The quantum mechanical calculations and the solvent effect on the photophysical properties showed that the lowest excited singlet state (S1) is a partially allowed π,π* state, while the close-lying S2 state is n,π* in nature. The efficiencies of fluorescence, S1→T1 intersystem crossing (ISC) and S1→ S0 internal conversion (IC) strongly depend on the energy gap between S1, and S2 and are explained in terms of the so-called proximity effect. In fact, for MA in cyclohexane, only the S1→ S0 internal conversion is operative, while in acetonitrile and ethanol, where the n.π* state is shifted to higher energy, the efficiencies of fluorescence and ISC increase significantly. The energy gap between S1 and S2 increases in MTA, where the furanic oxygen is replaced by a sulfur atom. Consequently, the solvent effect on the photophysical parameters of MTA is less marked than for MA; e.g. fluorescence and triplet-triplet absorption are also detectable in the nonpolar cyclohexane. The lowest excited singlet state of molecular oxygen O2(1Dg) was produced efficiently in polar solvents by energy transfer from the T1 state of MA and MTA. 相似文献
18.
A number of researchers have indicated that a direct reaction of acetylene with oxygen needs to be included in detailed reaction mechanisms in order to model observed flame speeds and induction times. Four pathways for the initiation of acetylene oxidation to chain propagation are considered and the rate constants are compared with values used in the mechanisms:
- 1 3O2 + HCCH to triplet adduct and reaction on the triplet surface
- 2 3O2 + HCCH to triplet adduct, conversion of triplet adduct to singlet adduct via collision in the reaction environment, with further reaction of the singlet adduct
- 3 1O2 + HCCH to singlet adduct
- 4 Isomerization of HCCH to vinylidene and then vinylidene insertion reaction with 3O2
19.
The structure and reactivity toward molecular nitrogen of vanadium diperoxo complexes, as well as the influence of the protonation and coordination of trifluoroacetate on the reactivity, were studied using the density functional method. The most stable form of the starting complex is the ozonide [V(O3)O2]–. The triplet state of the complex is formed with small energy expenses for electron transfer from the peroxo ligand to the vanadium atom to form VIV. The transfer of the O atom to the N2 molecule to form N2O is possible for several transition states. The nature of possible complexes and transition states retains upon protonation but the number of different structures increases depending on the ligand and the site of proton addition. Upon protonation the reactivity increases and the lowest activation barrier decreases from 27 to 20 kcal mol–1. The coordination of trifluoracetate anion also decreases the activation barrier for the intermolecular transfer of oxygen to the nitrogen molecule. 相似文献
20.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(32):9469-9473
The dark‐ and light‐adapted states of YtvA LOV domains exhibit distinct excited‐state behavior. We have employed high‐level QM(MS‐CASPT2)/MM calculations to study the photochemical reactions of the dark‐ and light‐adapted states. The photoreaction from the dark‐adapted state starts with an S1→T1 intersystem crossing followed by a triplet‐state hydrogen transfer from the thiol to the flavin moiety that produces a diradical intermediate, and a subsequent internal conversion that triggers a barrierless C−S bond formation in the S0 state. The energy profiles for these transformations are different for the four conformers of the dark‐adapted state considered. The photochemistry of the light‐adapted state does not involve the triplet state: photoexcitation to the S1 state triggers C−S bond cleavage followed by recombination in the S0 state; both these processes are essentially barrierless and thus ultrafast. The present work offers new mechanistic insights into the photoresponse of flavin‐containing blue‐light photoreceptors. 相似文献