Ultrafast transient absorption spectroelectrochemistry: femtosecond to nanosecond excited-state relaxation dynamics of the individual components of an anthraquinone redox couple

The third order non-linear optical response of a dicyanomethylene dihydrofuran compound (DCDHF-2V) was investigated using a Z-scan technique in picosecond and nanosecond time regimes. The results show that DCDHF-2V has excellent excited state non-linear refraction properties on both time regimes, and the non-linear refraction index is also solvent-dependent in the nanosecond regime. The excited state relaxation dynamics of DCDHF-2V were demystified via femtosecond transient absorption spectroscopy. The TA spectra reveal that the solvent viscosities have a substantial impact on the excited state relaxation of DCDHF-2V. The exotic photophysical phenomena in DCDHF-2V reported herein can shed new light on future development of small organic non-linear optical materials with large non-linear coefficients and fast response.

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Photoexcitation of Ge9− Clusters in THF: New Insights into the Ultrafast Relaxation Dynamics and the Influence of the Cation

Molecules ◽

10.3390/molecules25112639 ◽

2020 ◽

Vol 25 (11) ◽

pp. 2639

Author(s):

Nadine C. Michenfelder ◽

Christian Gienger ◽

Melina Dilanas ◽

Andreas Schnepf ◽

Andreas-Neil Unterreiner

Keyword(s):

Excited State ◽

Charge Transfer ◽

Conduction Band ◽

Near Infrared ◽

Transient Absorption ◽

Time Window ◽

Excess Electron ◽

Cluster Core ◽

Relaxation Dynamics ◽

Additional Time

We present a comprehensive femtosecond (fs) transient absorption study of the [Ge9(Hyp)3]− (Hyp = Si(SiMe3)3) cluster solvated in tetrahydrofuran (THF) with special emphasis on intra- and intermolecular charge transfer mechanisms which can be tuned by exchange of the counterion and by dimerization of the cluster. The examination of the visible and the near infrared (NIR) spectral range reveals four different processes of cluster dynamics after UV (267/258 nm) photoexcitation related to charge transfer to solvent and localized excited states in the cluster. The resulting transient absorption is mainly observed in the NIR region. In the UV-Vis range transient absorption of the (neutral) cluster core with similar dynamics can be observed. By transferring concepts of: (i) charge transfer to the solvent known from solvated Na− in THF and (ii) charge transfer in bulk-like materials on metalloid cluster systems containing [Ge9(Hyp)3]− moieties, we can nicely interpret the experimental findings for the different compounds. The first process occurs on a fs timescale and is attributed to localization of the excited electron in the quasi-conduction band/excited state which competes with a charge transfer to the solvent. The latter leads to an excess electron initially located in the vicinity of the parent cluster within the same solvent shell. In a second step, it can recombine with the cluster core with time constants in the picosecond (ps) timescale. Some electrons can escape the influence of the cluster leading to a solvated electron or after interaction with a cation to a contact pair both with lifetimes exceeding our experimentally accessible time window of 1 nanosecond (ns). An additional time constant on a tens of ps timescale is pronounced in the UV-Vis range which can be attributed to the recombination rate of the excited state or quasi conduction band of Ge9−. In the dimer, the excess electron cannot escape the molecule due to strong trapping by the Zn cation that links the two cluster cores.

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Excited State Dynamics of 7-Deazaguanosine and Guanosine 5’ Monophosphate

10.26434/chemrxiv.13262681.v2 ◽

2021 ◽

Author(s):

Sarah E. Krul ◽

Sean J. Hoehn ◽

Karl Feierabend ◽

Carlos Crespo-Hernández

Keyword(s):

Excited State ◽

Ground State ◽

Internal Conversion ◽

Transient Absorption ◽

Transient Absorption Spectroscopy ◽

Water Mixture ◽

Relaxation Dynamics ◽

Similar Time ◽

Excited State Dynamics ◽

Computational Calculations

Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways. In this study, the excited state dynamics of 7-deazaguanosine and guanosine 5’-monophosphate are investigated in aqueous and in a mixture of methanol and water using femtosecond broadband transient absorption spectroscopy following excitation at 267 nm. The transient spectra are collected using photon densities that ensure no parasitic multiphoton-induced signal from solvated electrons. The data can be fit satisfactorily using a two- or three-component kinetic model. By analyzing the results from steady-state, time-resolved, computational calculations, and the methanol-water mixture, the following general relaxation mechanism is proposed for both molecules, Lb ® La ® 1ps*(ICT) ® S0, where the 1ps*(ICT) stands for an intramolecular charge transfer excited singlet state with significant ps* character. In general, longer lifetimes for internal conversion are obtained for 7-deazaguanosine compared to guanosine 5’-monophosphate. Internal conversion of the 1ps*(ICT) state to the ground state occurs on a similar time scale of a few picoseconds in both molecules. Collectively, the results demonstrate that substitution of a single nitrogen for a methine (C-H) group at position seven of the guanine moiety stabilizes the 1pp* Lb and La states and alter the topology of their potential energy surfaces in such a way that the relaxation dynamics in 7-deazaguanosine are slowed down compared to those in guanosine 5’-monophosphate but not for the internal conversion of 1ps*(ICT) state to the ground state.

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Excited State Dynamics of 7-Deazaguanosine and Guanosine 5’ Monophosphate

10.26434/chemrxiv.13262681 ◽

2021 ◽

Author(s):

Sarah E. Krul ◽

Sean J. Hoehn ◽

Karl Feierabend ◽

Carlos Crespo-Hernández

Keyword(s):

Excited State ◽

Ground State ◽

Internal Conversion ◽

Transient Absorption ◽

Transient Absorption Spectroscopy ◽

Water Mixture ◽

Relaxation Dynamics ◽

Similar Time ◽

Excited State Dynamics ◽

Computational Calculations

Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways. In this study, the excited state dynamics of 7-deazaguanosine and guanosine 5’-monophosphate are investigated in aqueous and in a mixture of methanol and water using femtosecond broadband transient absorption spectroscopy following excitation at 267 nm. The transient spectra are collected using photon densities that ensure no parasitic multiphoton-induced signal from solvated electrons. The data can be fit satisfactorily using a two- or three-component kinetic model. By analyzing the results from steady-state, time-resolved, computational calculations, and the methanol-water mixture, the following general relaxation mechanism is proposed for both molecules, Lb ® La ® 1ps*(ICT) ® S0, where the 1ps*(ICT) stands for an intramolecular charge transfer excited singlet state with significant ps* character. In general, longer lifetimes for internal conversion are obtained for 7-deazaguanosine compared to guanosine 5’-monophosphate. Internal conversion of the 1ps*(ICT) state to the ground state occurs on a similar time scale of a few picoseconds in both molecules. Collectively, the results demonstrate that substitution of a single nitrogen for a methine (C-H) group at position seven of the guanine moiety stabilizes the 1pp* Lb and La states and alter the topology of their potential energy surfaces in such a way that the relaxation dynamics in 7-deazaguanosine are slowed down compared to those in guanosine 5’-monophosphate but not for the internal conversion of 1ps*(ICT) state to the ground state.

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Electrooxidation of Diclofenac in Synthetic Pharmaceutical Wastewater Using an Electrochemical Reactor Equipped with a Boron Doped Diamond Electrode

Journal of the Mexican Chemical Society ◽

10.29356/jmcs.v58i3.136 ◽

2017 ◽

Vol 58 (3) ◽

Cited By ~ 1

Author(s):

Gabriela Coria ◽

José L. Nava ◽

Gilberto Carreño

Keyword(s):

Energy Consumption ◽

Current Density ◽

Electrochemical Reactor ◽

Pharmaceutical Wastewater ◽

Boron Doped Diamond ◽

Linear Flow ◽

Diamond Electrode ◽

Boron Doped ◽

Boron Doped Diamond Electrode ◽

Set Up

This paper deals with the degradation of diclofenac by electrochemical oxidation in NaClO4 medium at neutral pH using a FM01-LC reactor equipped with a boron doped diamond electrode (BDD). Microelectrolysis studies were carried out to find the current density domain where hydroxyl radical (•OH) formation is favored, 10 ≤ j ≤ 20 mA cm-2. Electrolysis experiments at mean linear flow velocities of 14.6 ≤ u ≤ 58.4 cm s-1 were performed. The experimental set-up achieved 100% diclofenac mineralization with 78% current efficiency and energy consumption of 2.54 kWh m-3 at j = 15 mA cm-2 and u=29.2 cm s-1.

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Effect of the Mixture Composition of BmimBF4–Acetonitrile on the Excited-State Relaxation Dynamics of a Solar-Cell Dye D149: An Ultrafast Transient Absorption Study

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.1c05008 ◽

2021 ◽

Author(s):

Nishith Maity ◽

Piotr Piatkowski ◽

Kamil Polok ◽

François-Alexandre Miannay ◽

Abdenacer Idrissi

Keyword(s):

Excited State ◽

Solar Cell ◽

Transient Absorption ◽

Mixture Composition ◽

Absorption Study ◽

Relaxation Dynamics ◽

Ultrafast Transient Absorption

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Ultrafast excited state relaxation dynamics in a heteroleptic Ir(iii) complex, fac-Ir(ppy)2(ppz), revealed by femtosecond X-ray transient absorption spectroscopy

Inorganic Chemistry Frontiers ◽

10.1039/d0qi01510e ◽

2021 ◽

Author(s):

Jungkweon Choi ◽

Mina Ahn ◽

Jae Hyuk Lee ◽

Doo-Sik Ahn ◽

Hosung Ki ◽

...

Keyword(s):

Excited State ◽

Time Constant ◽

Absorption Spectroscopy ◽

Internal Conversion ◽

Transient Absorption ◽

Transient Absorption Spectroscopy ◽

Relaxation Dynamics ◽

X Ray ◽

Forbidden Transition ◽

Calculation Results

The experimental and calculation results demonstrate that the 3MLppzCT state generated by the spin-forbidden transition rapidly relaxes to 3MLppyCT through internal conversion process with a time constant of ∼450 fs.

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