Ultrafast Excited State Relaxation Dynamics of Branched Donor-π-Acceptor Chromophore:  Evidence of a Charge-Delocalized State

AbstractThe triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with 3MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the 3MLCT relaxation dynamics of [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the 3MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from 3MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen)2(dppz)]2+ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications.

Download Full-text

Excited state relaxation dynamics and up-conversion phenomena in Gd 3 (Al,Ga) 5 O 12 single crystals co-doped with holmium and ytterbium

Journal of Alloys and Compounds ◽

10.1016/j.jallcom.2015.09.262 ◽

2016 ◽

Vol 656 ◽

pp. 573-580 ◽

Cited By ~ 11

Author(s):

W. Ryba-Romanowski ◽

J. Komar ◽

T. Niedźwiedzki ◽

M. Głowacki ◽

M. Berkowski

Keyword(s):

Excited State ◽

Single Crystals ◽

Relaxation Dynamics ◽

Co Doped

Download Full-text

Excited-state dynamics of guanosine in aqueous solution revealed by time-resolved photoelectron spectroscopy: experiment and theory

Physical Chemistry Chemical Physics ◽

10.1039/c5cp04394h ◽

2015 ◽

Vol 17 (47) ◽

pp. 31978-31987 ◽

Cited By ~ 8

Author(s):

Franziska Buchner ◽

Berit Heggen ◽

Hans-Hermann Ritze ◽

Walter Thiel ◽

Andrea Lübcke

Keyword(s):

Aqueous Solution ◽

Excited State ◽

Photoelectron Spectroscopy ◽

Relaxation Dynamics ◽

Time Resolved ◽

Excited State Dynamics ◽

Spectroscopy Experiment

Time-resolved photoelectron spectroscopy is performed on aqueous guanosine solution to study its excited-state relaxation dynamics.

Download Full-text

Localization of a charge transfer excited state in molecular crystals: a direct confirmation by femtosecond diffuse reflectance spectroscopy

Chemical Physics Letters ◽

10.1016/0009-2614(96)00441-1 ◽

1996 ◽

Vol 256 (4-5) ◽

pp. 525-530 ◽

Cited By ~ 22

Author(s):

Tsuyoshi Asahi ◽

Yasutaka Matsuo ◽

Hiroshi Masuhara

Keyword(s):

Excited State ◽

Charge Transfer ◽

Diffuse Reflectance ◽

Diffuse Reflectance Spectroscopy ◽

Molecular Crystals ◽

Reflectance Spectroscopy ◽

A Charge ◽

Direct Confirmation

Download Full-text

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

Frontiers in Chemistry ◽

10.3389/fchem.2020.522974 ◽

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.

Download Full-text

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.

Download Full-text