Unusual Norrish Type I and Type II Nitro-Acyl Migration Transition State in the Photo-Uncaging of 1-Acyl-7-Nitroindolines Revealed by Computations

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

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Competition Between Cyclization and Unusual Norrish Type I and Type II Nitro-Acyl Migration Pathways in the Photouncaging of 1-Acyl-7-nitroindoline Revealed by Computations

10.26434/chemrxiv.11991651.v3 ◽

2020 ◽

Author(s):

Pierpaolo Morgante ◽

Charitha Guruge ◽

Yannick P. Ouedraogo ◽

Nasri Nesnas ◽

Roberto Peverati

Keyword(s):

Density Functional ◽

Acyl Migration ◽

Density Functional Theory Calculations ◽

Computational Procedure ◽

Quantum Yields ◽

Type I ◽

Type Ii ◽

Relative Quantum ◽

Norrish Type ◽

Migration Pathways

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

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Competition Between Cyclization and Unusual Norrish Type I and Type II Nitro-Acyl Migration Pathways in the Photouncaging of 1-Acyl-7-nitroindoline Revealed by Computations

10.26434/chemrxiv.11991651.v2 ◽

2020 ◽

Author(s):

Pierpaolo Morgante ◽

Charitha Guruge ◽

Yannick P. Ouedraogo ◽

Nasri Nesnas ◽

Roberto Peverati

Keyword(s):

Density Functional ◽

Acyl Migration ◽

Density Functional Theory Calculations ◽

Computational Procedure ◽

Quantum Yields ◽

Type I ◽

Type Ii ◽

Relative Quantum ◽

Norrish Type ◽

Migration Pathways

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

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Competition between cyclization and unusual Norrish type I and type II nitro-acyl migration pathways in the photouncaging of 1-acyl-7-nitroindoline revealed by computations

Scientific Reports ◽

10.1038/s41598-020-79701-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Pierpaolo Morgante ◽

Charitha Guruge ◽

Yannick P. Ouedraogo ◽

Nasri Nesnas ◽

Roberto Peverati

Keyword(s):

Density Functional ◽

Acyl Migration ◽

Density Functional Theory Calculations ◽

Quantum Yields ◽

Type I ◽

Type Ii ◽

Migration Pathway ◽

Norrish Type ◽

Triplet Excited States ◽

Migration Pathways

AbstractThe 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and an acyl migration pathway, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish type I and a 1,6-nitro-acyl variation of a Norrish type II mechanism, which is reported here for the first time. We also found negligible energetic differences in the uncaging mechanisms of the 4-methoxy-5,7-dinitroindolinyl (MDNI) cages and their mononitro analogues (MNI). We traced the experimentally observed improved quantum yields of MDNI to a higher population of the reactants in the triplet surface. This fact is supported by a more favorable intersystem crossing due to the availability of a higher number of triplet excited states with the correct symmetry in MDNI than in MNI. Our findings may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.

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Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.17.21 ◽

2021 ◽

Vol 17 ◽

pp. 210-223

Author(s):

Dongyang Chen ◽

Eli Zysman-Colman

Keyword(s):

Density Functional ◽

Density Functional Theory Calculations ◽

Delayed Fluorescence ◽

Type I ◽

Type Ii ◽

Triplet Energy ◽

Thermally Activated Delayed Fluorescence ◽

Thermally Activated ◽

Deep Blue ◽

Donor Acceptor

The trifluoromethyl group has been previously explored as a non-conjugated electron-withdrawing group in donor–acceptor thermally activated delayed fluorescence (TADF) emitters. In the present study, we investigate computationally the potential of other fluorine-containing acceptors, trifluoromethoxy (OCF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5), within two families of donor–acceptor TADF emitters. Time-dependent density functional theory calculations indicate that when only two ortho-disposed carbazole donors are used (Type I molecules), the lowest-lying triplet state possesses locally excited (LE) character while the lowest-lying singlet state possesses charge-transfer character. When five carbazole donors are present in the emitter design (Type II molecules), now both S1 and T1 states possess CT character. For molecules 2CzOCF 3 and 5CzOCF 3 , the singlet energies are predicted to be 3.92 eV and 3.45 eV; however, the singlet-triplet energy gaps, ΔE STs, are predicted to be large at 0.46 eV and 0.37 eV, respectively. The compounds 2CzCF 3 , 2CzSCF 3 , and 2CzSF 5 , from Type I molecules, show significant promise as deep blue TADF emitters, possessing high calculated singlet energies in the gas phase (3.62 eV, 3.66 eV, and 3.51 eV, respectively) and small, ΔE STs, of 0.17 eV, 0.22 eV, and 0.07 eV, respectively. For compounds 5CzSCF 3 and 5CzSF 5 , from Type II molecules, the singlet energies are stabilized to 3.24 eV and 3.00 eV, respectively, while ΔE STs are 0.27 eV and 0.12 eV, respectively, thus both show promise as blue or sky-blue TADF emitters. All these six molecules possess a dense number of intermediate excited states between S1 and T1, thus likely leading to a very efficient reverse intersystem crossing in these compounds.

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Photochemistry of Ketones in Carbon Tetrachloride Solution

Canadian Journal of Chemistry ◽

10.1139/v73-216 ◽

1973 ◽

Vol 51 (9) ◽

pp. 1435-1440 ◽

Cited By ~ 13

Author(s):

J. O. Pavlik ◽

P. I. Plooard ◽

A. C. Somersall ◽

J. E. Guillet

Keyword(s):

Energy Transfer ◽

Carbon Tetrachloride ◽

Quantum Yields ◽

Type I ◽

Type Ii ◽

Definitive Evidence ◽

Carbon Tetrachloride Solution ◽

Radiationless Energy Transfer ◽

Norrish Type ◽

Low Efficiency

Acetone, chloroacetone, 4-heptanone, 8-pentadecanone, 12-tricosanone, and dimethyl γ-keto pimellate were photolyzed at 3130 Å in carbon tetrachloride solution. The quantum yields of C2Cl6 formed, the decrease in Norrish type I and type II products, the copious yields of HCl and the Stern–Volmer quenching of ketone fluorescence by carbon tetrachloride provide definitive evidence for energy transfer which is rationalized by an exciplex mechanism of low efficiency. The excited [n,π*]1 state of the ketone forms a loose complex with the CCl4 and radiationless energy transfer leads to dissociation of the CCl4 in the primary chemical step.

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Transparent Ion-Exchange Membrane Exhibiting Intense Emission under a Specific pH Condition Based on Polypyridyl Ruthenium(II) Complex with Two Imidazophenanthroline Groups

Membranes ◽

10.3390/membranes11060400 ◽

2021 ◽

Vol 11 (6) ◽

pp. 400

Author(s):

Hajime Kamebuchi ◽

Satoshi Tamaki ◽

Atsushi Okazawa ◽

Norimichi Kojima

Keyword(s):

Ion Exchange ◽

Emission Intensity ◽

Density Functional ◽

Emission Spectra ◽

Density Functional Theory Calculations ◽

Ion Exchange Membrane ◽

Quantum Yields ◽

Relative Emission Intensity ◽

Nafion Film ◽

Exchange Membrane

The development and the photophysical behavior of a transparent ion-exchange membrane based on a pH-sensitive polypyridyl ruthenium(II) complex, [(bpy)2RuII(H2bpib)RuII(bpy)2](ClO4)4 (bpy = 2,2′-bipyridine, H2bpib = 1,4-bis([1,10]phenanthroline[5,6-d]-imidazol-2-yl)benzene), are experimentally and theoretically reported. The emission spectra of [(bpy)2RuII(H2bpib)RuII(bpy)2]@Nafion film were observed between pH 2 and pH 11 and showed the highest relative emission intensity at pH 5 (λmaxem = 594.4 nm). The relative emission intensity of the film significantly decreased down to 75% at pH 2 and 11 compared to that of pH 5. The quantum yields (Φ) and lifetimes (τ) showed similar correlations with respect to pH, Φ = 0.13 and τ = 1237 ns at pH 5, and Φ = 0.087 and τ = 1014 ns and Φ = 0.069 and τ = 954 ns at pH 2 and pH 11, respectively. These photophysical data are overall considerably superior to those of the solution, with the radiative- (kr) and non-radiative rate constants (knr) at pH 5 estimated to be kr = 1.06 × 105 s−1 and knr = 7.03 × 105 s−1. Density functional theory calculations suggested the contribution of ligand-to-ligand- and intraligand charge transfer to the imidazolium moiety in Ru-H3bpib species, implying that the positive charge on the H3bpib ligand works as a quencher. The Ru-Hbpib species seems to enhance non-radiative deactivation by reducing the energy of the upper-lying metal-centered excited state. These would be responsible for the pH-dependent “off-on-off” emission behavior.

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Interfacial defect engineering and Photocatalysis Properties of hBN/MX2(M = Mo, W, and X = S, Se) Heterostructures

Chinese Physics B ◽

10.1088/1674-1056/ac43b2 ◽

2021 ◽

Author(s):

Zhihai Sun ◽

Jiaxi Liu ◽

Ying Zhang ◽

Ziyuan Li ◽

Leyu Peng ◽

...

Keyword(s):

Density Functional ◽

Density Functional Theory Calculations ◽

Band Alignment ◽

Type I ◽

Defect Engineering ◽

Wide Range ◽

Interfacial Defects ◽

Significant Research ◽

P Type ◽

The Impact

Abstract Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential in a wide range of applications such as electronics, optoelectronic, and heterocatalysis. In this work, the impact of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX2(M = Mo, W, and X = S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX2 can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure was maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed to the type-II heterostructrue as VB defect and p-type doping was introduced in the hBN sublayer. This could be profitable for the separation of photo-generated electron−hole pairs at the interfaces and is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(BeB)/MoS2, hBN(BeB)/MoSe2, and hBN(VN)/MoSe2 were achieved, showing reducing band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX2 heterostructures via interfacial defects.

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Competition Between Azido Cleavage and Triplet Nitrene Formation in Azidomethylacetophenones

Australian Journal of Chemistry ◽

10.1071/ch10331 ◽

2010 ◽

Vol 63 (12) ◽

pp. 1645 ◽

Cited By ~ 8

Author(s):

Ranaweera A. A. Upul Ranaweera ◽

Yu Zhao ◽

Sivaramakrishnan Muthukrishnan ◽

Christopher Keller ◽

Anna D. Gudmundsdottir

Keyword(s):

Transition State ◽

Density Functional ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Density Functional Theory Calculations ◽

Laser Flash ◽

Saturated Solution ◽

Azido Group ◽

Benzyl Radicals ◽

Saturated Solutions

Photolysis of p- and m-azidomethylacetophenone (1a, 1b) in argon-saturated solutions yields predominantly imine 2a, 2b, whereas irradiation of 1a, 1b in oxygen-saturated solutions results in heterocycles 3a, 3b, aldehydes 4a, 4b and nitriles 5a, 5b. Density functional theory calculations place the energy of the first and second excited state of the triplet ketones (T1K and T2K) in 1a, 1b in close proximity to each other. The triplet transition state for cleaving the C–N bond in 1a, 1b to form azido and benzyl radicals 1aB, 1bB is located only 3 kcal mol–1 (1 kcal = 4.184 kJ) above T1K, indicating that azido cleavage is feasible. The calculations place the energy of the triplet azido group (TA) in 1a, 1b ∼25 kcal mol–1 below T1K; thus, this process is also easily accessible via energy transfer. Further, the transition state barrier for TA to expel N2 and form triplet nitrenes is less than 1 kcal mol–1 above TA in 1a, 1b. Laser flash photolysis of 1a, 1b reveals the formation of the triplet excited ketones of 1a, 1b, which decay to form benzyl radicals 1aB, 1bB and triplet alkylnitrenes. The triplet ketones and the benzyl radicals are quenched with molecular oxygen at rates close to diffusion, whereas the triplet nitrenes react more slowly with oxygen (∼5 × 105 M–1 s–1). We conclude that the triplet alkylnitrenes intercept the benzyl radicals to form 2 in argon-saturated solution, whereas the benzyl radicals are trapped to form 4 in oxygen-saturated solution; thus, the triplet nitrenes react with oxygen to form 3.

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