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

Molecules ◽  
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.

scholarly journals Tunable Non-linear Refraction Properties and Ultrafast Excited State Dynamics of Dicyanomethylene Dihydrofuran Derivative

2020 ◽  
Vol 8 ◽  
Author(s):  
Linpo Yang ◽  
Zhongguo Li ◽  
Taihui Wei ◽  
Liming Zhou ◽  
Feng Li ◽  
...  
Keyword(s):  
Excited State ◽  
Transient Absorption ◽  
Refraction Index ◽  
Fast Response ◽  
Transient Absorption Spectroscopy ◽  
Relaxation Dynamics ◽  
Substantial Impact ◽  
Femtosecond Transient Absorption ◽  
Non Linear ◽  
Linear Optical

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.

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

2022 ◽  
Author(s):  
Sofia Goia ◽  
Matthew A. P. Turner ◽  
Jack M. Woolley ◽  
Michael D. Horbury ◽  
Alexandra J. Borrill ◽  
...  
Keyword(s):  
Excited State ◽  
Transient Absorption ◽  
Reactive Intermediates ◽  
Active Species ◽  
Relaxation Dynamics ◽  
Boron Doped Diamond ◽  
Boron Doped ◽  
Redox Active ◽  
Set Up ◽  
The Individual

A spectroelectrochemical set-up using a boron doped diamond mesh electrode is presented; from ultrafast photodynamics to steady-state, the photochemistry and photophysics of redox active species and their reactive intermediates can be investigated.

Direct evidence of solvent polarity governing the intramolecular charge and energy transfer: ultrafast relaxation dynamics of push–pull fluorene derivatives

2019 ◽  
Vol 21 (21) ◽  
pp. 11087-11102 ◽  
Author(s):  
Afeefah U. Neelambra ◽  
Chinju Govind ◽  
Tessy T. Devassia ◽  
Guruprasad M. Somashekharappa ◽  
Venugopal Karunakaran
Keyword(s):  
Energy Transfer ◽  
Charge Transfer ◽  
Emission Spectroscopy ◽  
Direct Evidence ◽  
Transient Absorption ◽  
Intramolecular Charge Transfer ◽  
Solvent Polarity ◽  
Relaxation Dynamics ◽  
Ultrafast Relaxation ◽  
Absorption And Emission Spectroscopy

The occurrence of intramolecular charge transfer along with energy transfer controlled by the polarity of solvent is revealed by femtosecond and nanosecond transient absorption and emission spectroscopy.

Excited-state molecular structures captured by X-ray transient absorption spectroscopy: a decade and beyond

2010 ◽  
Vol 66 (2) ◽  
pp. 240-251 ◽  
Author(s):  
Lin X. Chen ◽  
Xiaoyi Zhang ◽  
Jenny V. Lockard ◽  
Andrew B. Stickrath ◽  
Klaus Attenkofer ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Metal Complexes ◽  
Absorption Spectroscopy ◽  
Chemical Reaction ◽  
Transient Absorption ◽  
Molecular Structures ◽  
Transient Absorption Spectroscopy ◽  
Reaction Pathways ◽  
X Ray

Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution–solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled.

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

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

<p>Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways.<b> </b>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, L<sub>b</sub> ® L<sub>a</sub> ® <sup>1</sup>ps*(ICT) ® S<sub>0</sub>, where the <sup>1</sup>ps*(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 <sup>1</sup>ps*(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 <sup>1</sup>pp* L<sub>b</sub> and L<sub>a</sub> 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 <sup>1</sup>ps*(ICT) state to the ground state.</p>

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

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

<p>Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways.<b> </b>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, L<sub>b</sub> ® L<sub>a</sub> ® <sup>1</sup>ps*(ICT) ® S<sub>0</sub>, where the <sup>1</sup>ps*(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 <sup>1</sup>ps*(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 <sup>1</sup>pp* L<sub>b</sub> and L<sub>a</sub> 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 <sup>1</sup>ps*(ICT) state to the ground state.</p>

Ultrafast relaxation dynamics of phosphine-protected, rod-shaped Au20 clusters: interplay between solvation and surface trapping

2014 ◽  
Vol 16 (34) ◽  
pp. 18288-18293 ◽  
Author(s):  
Meng Zhou ◽  
Saran Long ◽  
Xiankai Wan ◽  
Yang Li ◽  
Yingli Niu ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Intramolecular Charge Transfer ◽  
Relaxation Dynamics ◽  
Coherent Oscillation ◽  
Ultrafast Relaxation

Excited-state intramolecular charge transfer dynanmics and coherent oscillation of ligand-protected rod shaped Au20 clusters were modulated through the competition between solvation and surface trapping.

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