Halogen-Bond Assisted Photoinduced Electron Transfer

The formation of a halogen-bond (XB) complex in the excited state was recently reported with a quadrupolar acceptor–donor–acceptor dye in two iodine-based liquids (J. Phys. Chem. Lett. 2017, 8, 3927–3932). The ultrafast decay of this excited complex to the ground state was ascribed to an electron transfer quenching by the XB donors. We examined the mechanism of this process by investigating the quenching dynamics of the dye in the S1 state using the same two iodo-compounds diluted in inert solvents. The results were compared with those obtained with a non-halogenated electron acceptor, fumaronitrile. Whereas quenching by fumaronitrile was found to be diffusion controlled, that by the two XB compounds is slower, despite a larger driving force for electron transfer. A Smoluchowski–Collins–Kimball analysis of the excited-state population decays reveals that both the intrinsic quenching rate constant and the quenching radius are significantly smaller with the XB compounds. These results point to much stronger orientational constraint for quenching with the XB compounds, indicating that electron transfer occurs upon formation of the halogen bond.

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Photoinduced Electron Transfer Reactions of Water Soluble Porphyrins in Zeolite Environment

10.21203/rs.3.rs-207972/v1 ◽

2021 ◽

Author(s):

Anbazhagan Venkattappan ◽

Kandavelu Velappan ◽

Renganathan Rajalingam

Keyword(s):

Electron Transfer ◽

Excited State ◽

Water Solution ◽

Total Concentration ◽

Water Soluble ◽

Bet Surface Area ◽

X Ray Diffraction ◽

Quenching Rate ◽

Glycerol Water ◽

Quenching Rate Constant

Abstract Excited state interactions of zeolite adsorbed porphyrins have been investigated by steady state luminescence quenching technique with certain antioxidants such as reduced glutathione, ascorbic acid and L-cysteine. The zeolite supported porphyrins, meso-tetra (N-methyl-4-pyridyl) porphyrin (H2TMPyP4+) and zinc tetra(N-methyl-4-pyridyl) porphyrin (ZnTMPyP4+) was prepared and characterized by various techniques such as Diffuse Reflectance Spectra (DRS), Scanning Electron Microscope (SEM), powder X-Ray Diffraction (XRD) and BET surface area. The interaction of zeolites with porphyrins are shown to increase the lifetime of the singlet excited state of porphyrins and decays are biphasic in nature. The splitting of the emission band of porphyrins occurs in 1:1 glycerol: water solution due to the changes in the dielectric of the solvation sphere associated with porphyrin. The Stern-Volmer plots of I0/I vs quencher total concentration [Q] were linear in the whole range of [Q] used. This study revealed effective quenching for zinc porphyrin compared to free base porphyrin. The effect of quenchers and zeolite acidity has also been studied. Quenching rate constant (kq) is on the order of 109 M−1 s−1. The quenching reaction obeys Rehm-Weller Equation and is shown to be due to thermodynamically favoured electron transfer from quenchers to the excited singlet state of porphyrins (reductive quenching).

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Two-electron transfer stabilized by excited-state aromatization

Nature Communications ◽

10.1038/s41467-019-12986-w ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 1

Author(s):

Jinseok Kim ◽

Juwon Oh ◽

Seongchul Park ◽

Jose L. Zafra ◽

Justin R. DeFrancisco ◽

...

Keyword(s):

Electron Transfer ◽

Excited State ◽

Excited States ◽

Transfer Process ◽

Comprehensive Understanding ◽

Electron Transfer Process ◽

Photoactive Materials ◽

Donor Acceptor ◽

Scientific Significance

Abstract The scientific significance of excited-state aromaticity concerns with the elucidation of processes and properties in the excited states. Here, we focus on TMTQ, an oligomer composed of a central 1,6-methano[10]annulene and 5-dicyanomethyl-thiophene peripheries (acceptor-donor-acceptor system), and investigate a two-electron transfer process dominantly stabilized by an aromatization in the low-energy lying excited state. Our spectroscopic measurements quantitatively observe the shift of two π-electrons between donor and acceptors. It is revealed that this two-electron transfer process accompanies the excited-state aromatization, producing a Baird aromatic 8π core annulene in TMTQ. Biradical character on each terminal dicyanomethylene group of TMTQ allows a pseudo triplet-like configuration on the 8π core annulene with multiexcitonic nature, which stabilizes the energetically unfavorable two-charge separated state by the formation of Baird aromatic core annulene. This finding provides a comprehensive understanding of the role of excited-state aromaticity and insight to designing functional photoactive materials.

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(Invited) Excited State Dynamics and Ultrafast Electron Transfer in β-Iodo Substituted Bdp and ADP Donor-Acceptor Systems Featuring Fullerene.

ECS Meeting Abstracts ◽

10.1149/ma2019-01/11/782 ◽

2019 ◽

Keyword(s):

Electron Transfer ◽

Excited State ◽

Excited State Dynamics ◽

Donor Acceptor ◽

Ultrafast Electron Transfer

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Ground-state electron transfer in all-polymer donor–acceptor heterojunctions

Nature Materials ◽

10.1038/s41563-020-0618-7 ◽

2020 ◽

Vol 19 (7) ◽

pp. 738-744 ◽

Cited By ~ 14

Author(s):

Kai Xu ◽

Hengda Sun ◽

Tero-Petri Ruoko ◽

Gang Wang ◽

Renee Kroon ◽

...

Keyword(s):

Electron Transfer ◽

Ground State ◽

State Electron ◽

Donor Acceptor ◽

Ground State Electron

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Role of active site conformational changes in photocycle activation of the AppA BLUF photoreceptor

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1621393114 ◽

2017 ◽

Vol 114 (7) ◽

pp. 1480-1485 ◽

Cited By ~ 17

Author(s):

Puja Goyal ◽

Sharon Hammes-Schiffer

Keyword(s):

Electron Transfer ◽

Free Energy ◽

Excited State ◽

Charge Transfer ◽

Conformational Changes ◽

Ground State ◽

Active Site ◽

Locally Excited ◽

Proton Relay ◽

Locally Excited State

Blue light using flavin adenine dinucleotide (BLUF) proteins are essential for the light regulation of a variety of physiologically important processes and serve as a prototype for photoinduced proton-coupled electron transfer (PCET). Free-energy simulations elucidate the active site conformations in the AppA (activation of photopigment and puc expression) BLUF domain before and following photoexcitation. The free-energy profile for interconversion between conformations with either Trp104 or Met106 closer to the flavin, denoted Trpin/Metout and Trpout/Metin, reveals that both conformations are sampled on the ground state, with the former thermodynamically favorable by ∼3 kcal/mol. These results are consistent with the experimental observation of both conformations. To analyze the proton relay from Tyr21 to the flavin via Gln63, the free-energy profiles for Gln63 rotation were calculated on the ground state, the locally excited state of the flavin, and the charge-transfer state associated with electron transfer from Tyr21 to the flavin. For the Trpin/Metout conformation, the hydrogen-bonding pattern conducive to the proton relay is not thermodynamically favorable on the ground state but becomes more favorable, corresponding to approximately half of the configurations sampled, on the locally excited state. The calculated energy gaps between the locally excited and charge-transfer states suggest that electron transfer from Tyr21 to the flavin is more facile for configurations conducive to proton transfer. When the active site conformation is not conducive to PCET from Tyr21, Trp104 can directly compete with Tyr21 for electron transfer to the flavin through a nonproductive pathway, impeding the signaling efficiency.

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Bimolecular electron transfer reactions in coumarin–amine systems: Donor–acceptor orientational effect on diffusion-controlled reaction rates

Journal of Molecular Structure ◽

10.1016/j.molstruc.2007.07.042 ◽

2008 ◽

Vol 878 (1-3) ◽

pp. 84-94 ◽

Cited By ~ 18

Author(s):

A.K. Satpati ◽

S. Nath ◽

M. Kumbhakar ◽

D.K. Maity ◽

S. Senthilkumar ◽

...

Keyword(s):

Electron Transfer ◽

Reaction Rates ◽

Transfer Reactions ◽

Electron Transfer Reactions ◽

Orientational Effect ◽

Diffusion Controlled ◽

Donor Acceptor ◽

Diffusion Controlled Reaction

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Phenyl Substitution Effects on Triplet–Triplet Absorption Spectra: I. Study of 1,3,6,8-Tetraphenylpyrene

Canadian Journal of Chemistry ◽

10.1139/v75-466 ◽

1975 ◽

Vol 53 (21) ◽

pp. 3269-3275 ◽

Cited By ~ 10

Author(s):

C. Rullière ◽

E. C. Colson ◽

P. C. Roberge

Keyword(s):

Absorption Spectrum ◽

Triplet State ◽

Absorption Spectra ◽

Rate Constant ◽

Theoretical Calculations ◽

Vibrational Structure ◽

Substitution Effects ◽

Quenching Rate ◽

Diffusion Controlled ◽

Quenching Rate Constant

The triplet–triplet (T–T) absorption spectrum of 1,3,6,8-tetraphenylpyrene (TPP) was measured from 400 to 620 nm. The data obtained are compared with theoretical calculations using the Ruedenberg–Scherr FEMO model. A planar triplet state is evidenced by fine vibrational structure. The T–T quenching rate constant measured (1.3 ± 0.1 × 109 M−1 s−1) is 20% of the expected diffusion-controlled value.

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Chromophore-radical excited state antiferromagnetic exchange controls the sign of photoinduced ground state spin polarization

Chemical Science ◽

10.1039/d1sc02965g ◽

2021 ◽

Author(s):

Martin L. Kirk ◽

David A. Shultz ◽

Patrick Hewitt ◽

Daniel E. Stasiw ◽

Ju Chen ◽

...

Keyword(s):

Excited State ◽

Spin Polarization ◽

Ground State ◽

Electron Spin Polarization ◽

Organic Radical ◽

Antiferromagnetic Exchange ◽

Ground State Spin ◽

Donor Acceptor ◽

State Spin ◽

Ground State Electron

A change in the sign of the ground state electron spin polarization (ESP) is reported in complexes where an organic radical (nitronylnitroxide, NN) is covalently attached to a donor–acceptor chromophore via two different meta-phenylene bridges.

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Exclusive triplet electron transfer leading to long-lived radical ion-pair formation in an electron rich platinum porphyrin covalently linked to fullerene dyad

Chemical Communications ◽

10.1039/d0cc02007a ◽

2020 ◽

Vol 56 (45) ◽

pp. 6058-6061 ◽

Cited By ~ 3

Author(s):

Dili R. Subedi ◽

Habtom B. Gobeze ◽

Yuri E. Kandrashkin ◽

Prashanth K. Poddutoori ◽

Art van der Est ◽

...

Keyword(s):

Electron Transfer ◽

Excited State ◽

Ion Pair ◽

Pair Formation ◽

Triplet Excited State ◽

Ion Pair Formation ◽

Donor Acceptor ◽

Platinum Porphyrin ◽

Covalently Linked ◽

Pair Energy

Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the triplet excited state of a photosensitizer, is established in a novel donor–acceptor conjugate.

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