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355 results on '"Gurzadyan, Gagik G."'

1. Intramolecular benzene excimer formation in 13,14-diphenyldibenzo[b,j][4,7]phenanthroline.

Author

Lin, Jiafen, Ma, Lin, Zhao, Yilun, Long, Saran, Li, Tianjiao, Ghosh, Animesh, Grimsdale, Andrew C., Peng, Xiaojun, Sun, Licheng, and Gurzadyan, Gagik G.

Subjects
FLUORESCENCE spectroscopy, EXCITED states, PHENANTHROLINE, BENZENE, FLUORESCENCE
Abstract

13,14-diphenyldibenzo[b,j][4,7]phenanthroline (DBP3) in various solvents was studied by time-resolved fluorescence and fs transient absorption (fs-TA) spectroscopy. An intramolecular benzene excimer is demonstrated to form within DBP3; it exhibits strong redshifted emission with maximum at 540–640 nm. "Intrinsic" fluorescence from DBP3 is dramatically quenched down to τ = 50–400 fs in all the solvents studied. Fs-TA and time-resolved fluorescence spectra have proved that relaxed intramolecular benzene excimer is formed from S1 state via hot excimer state with three lifetime components: 50 fs, ∼3.5 ps, and ∼25 ps, which are of the inertial (electronic) and diffusive parts of the relaxation due to solute–solvent interaction. Formation of triplet states via intersystem crossing was observed directly from the upper excited electronic states of DBP3. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Polaron Self-localization in White-light Emitting Hybrid Perovskites

Author

Cortecchia, Daniele, Yin, Jun, Bruno, Annalisa, Lo, Shu-Zee Alencious, Gurzadyan, Gagik G., Mhaisalkar, Subodh, Brédas, Jean-Luc, and Soci, Cesare

Subjects
Condensed Matter - Materials Science
Abstract

Two-dimensional (2D) perovskites with general formula $APbX_4$ are attracting increasing interest as solution processable, white-light emissive materials. Recent studies have shown that their broadband emission is related to the formation of intra-gap color centers; however, the nature and dynamics of the emissive species have remained elusive. Here we show that the broadband photoluminescence of the 2D perovskites $(EDBE)PbCl_4$ and $(EDBE)PbBr_4$ stems from the localization of small polarons within the lattice distortion field. Using a combination of spectroscopic techniques and first-principles calculations, we infer the formation of ${Pb_2}^{3+}$, $Pb^{3+}$, and ${X_2}^-$ (where X=Cl or Br) species confined within the inorganic perovskite framework. Due to strong Coulombic interactions, these species retain their original excitonic character and form self-trapped polaron-excitons acting as radiative color centers. These findings are expected to be applicable to a broad class of white-light emitting perovskites with large polaron relaxation energy., Comment: 34 pages, 15 figures, 3 tables

Published
2016

13. Large Scale Synthesis of Bi-layer Graphene in Strongly Coupled Stacking Order

Author

Luo, Zhiqiang, Yu, Ting, Shang, Jingzhi, Wang, Yingying, Lim, Sanhua, Liu, Lei, Gurzadyan, Gagik G., Shen, Zexiang, and Lin, Jianyi

Subjects
Condensed Matter - Materials Science
Abstract

Large scale synthesis of single layer graphene (SLG) by chemical vapor deposition (CVD) has received a lot of attention recently. However, CVD synthesis of AB stacked bi-layer graphene (BLG) is still a challenging work. Here we report synthesis of BLG homogeneously in large area by thermal CVD. The 2D Raman band of CVD BLG splits into four components, suggesting splitting of electronic bands due to strong interlayer coupling. The splitting of electronic bands in CVD BLG is further evidenced by the study of near infrared (NIR) absorption and carrier dynamics probed by transient absorption spectroscopy. Ultraviolet photoelectron spectroscopy invesigation also indiates CVD BLG possesses different electronic structures from those of CVD SLG. The growth mechanism of BLG is found to be related to catalystic activity of copper (Cu)surface, which is determined by purity of Cu foils employed in CVD process. Our work showsthat strongly coupled or even AB stacked BLG can be grown on Cu foils in large scale, which isof particular importance for device applications based on their split electronic bands, Comment: 20 pages, 8 Figures

Published
2010

17. Toward efficient photochemistry from upper excited electronic states: Detection of long S2 lifetime of perylene.

Author

Ni, Wenjun, Gurzadyan, Gagik G., Sun, Licheng, and Gelin, Maxim F.

Subjects
*EXCITED states, *PERYLENE, *PHOTOCHEMISTRY
Abstract

A long 0.9 ps lifetime of the upper excited singlet state in perylene is resolved by femtosecond pump–probe measurements under ultraviolet (4.96 eV) excitation and further validated by theoretical simulations of transient absorption kinetics. This finding prompts exploration and development of novel perylene-based materials for upper excited state photochemistry applications. [ABSTRACT FROM AUTHOR]

Published
2021
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26. Applications of Nonlinear Crystals

Author

Dmitriev, Valentin G., Gurzadyan, Gagik G., Nikogosyan, David N., Lotsch, Helmut K. V., editor, Dmitriev, Valentin G., Gurzadyan, Gagik G., and Nikogosyan, David N.

Published
1997
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28. Optics of Nonlinear Crystals

Author

Dmitriev, Valentin G., Gurzadyan, Gagik G., Nikogosyan, David N., Lotsch, Helmut K. V., editor, Dmitriev, Valentin G., Gurzadyan, Gagik G., and Nikogosyan, David N.

Published
1997
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30. Applications of Nonlinear Crystals

Author

Dmitriev, Valentin G., Gurzadyan, Gagik G., Nikogosyan, David N., Lotsch, Helmut K. V., editor, Siegman, A. E., editor, Dmitriev, Valentin G., Gurzadyan, Gagik G., and Nikogosyan, David N.

Published
1991
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31. Nonlinear Optical Properties of Crystals

Author

Dmitriev, Valentin G., Gurzadyan, Gagik G., Nikogosyan, David N., Lotsch, Helmut K. V., editor, Siegman, A. E., editor, Dmitriev, Valentin G., Gurzadyan, Gagik G., and Nikogosyan, David N.

Published
1991
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32. Optics of Nonlinear Crystals

Author

Dmitriev, Valentin G., Gurzadyan, Gagik G., Nikogosyan, David N., Lotsch, Helmut K. V., editor, Siegman, A. E., editor, Dmitriev, Valentin G., Gurzadyan, Gagik G., and Nikogosyan, David N.

Published
1991
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33. Water oxidation by a noble metal-free photoanode modified with an organic dye and a molecular cobalt catalyst

Author

Zhu, Yong, Wang, Degao, Ni, Wenjun, Gurzadyan, Gagik G., Sun, Licheng, Meyer, Thomas J., Li, Fei, Zhu, Yong, Wang, Degao, Ni, Wenjun, Gurzadyan, Gagik G., Sun, Licheng, Meyer, Thomas J., and Li, Fei

Abstract

A low-cost and easy-to-construct dye-sensitized photoanode for water oxidation was prepared by co-loading a new triphenylamine donor-acceptor organic chromophore (D1) and a Co4O4 cobalt cubane-based water oxidation catalyst (CoF) on TiO2 thin films. As the first example of a molecular catalyst-based, noble metal-free, dye-sensitized photoanode, the electrode, TiO2|D1,CoF, produces a higher photocurrent than other noble metal-free, dye-sensitized photoanodes with a relatively high faradaic efficiency for O2 production. The success of the dyad system lies in retarded interfacial charge recombination and extended light absorption both of which take advantage of the pyridine anchor-functionalized chromophore. In addition, the CoF catalyst, decorated with hydrophobic aliphatic chains, serves as a protective layer for stabilizing the organic dyes on electrode surfaces. Transient absorption measurement suggests the accumulation of oxidative equivalents on CoF by electron transfer on the TiO2 surface. The results and design principles presented here demonstrate the use of molecular engineering as a powerful tool for the exploration of low-cost solar water-splitting devices., QC 20230124

Published
2022
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48. Atomically Dispersed Indium‐Copper Dual‐Metal Active Sites Promoting C−C Coupling for CO2 Photoreduction to Ethanol.

Author

Shi, Hainan, Wang, Haozhi, Zhou, Yichen, Li, Jiahui, Zhai, Panlong, Li, Xiangyang, Gurzadyan, Gagik G., Hou, Jungang, Yang, Hong, and Guo, Xinwen

Subjects
COUPLING reactions (Chemistry), ACTIVATION energy, CHARGE exchange, ELECTRON density, ETHANOL, CHARGE transfer, PHOTOREDUCTION
Abstract

Photoreduction of CO2 to C2+ solar fuel is a promising carbon‐neutral technology for renewable energy. This strategy is challenged by its low productivity due to low efficiency in multielectron utilization and slow C−C coupling kinetics. This work reports a dual‐metal photocatalyst consisting of atomically dispersed indium and copper anchored on polymeric carbon nitride (InCu/PCN), on which the photoreduction of CO2 delivered an excellent ethanol production rate of 28.5 μmol g−1 h−1 with a high selectivity of 92 %. Coupled experimental investigation and DFT calculations reveal the following mechanisms underpinning the high performance of this catalyst. Essentially, the In−Cu interaction enhances the charge separation by accelerating charge transfer from PCN to the metal sites. Indium also transfers electrons to neighboring copper via Cu−N−In bridges, increasing the electron density of copper active sites. Furthermore, In−Cu dual‐metal sites promote the adsorption of *CO intermediates and lower the energy barrier of C−C coupling. [ABSTRACT FROM AUTHOR]

Published
2022
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49. Does Twisted π-Conjugation Framework Always Induce Efficient Intersystem Crossing? A Case Study with Benzo[b]- and [a]Phenanthrene-Fused BODIPY Derivatives and Identification of a Dark State

Author

Yan, Yuxin, primary, Sukhanov, Andrei A., additional, Bousquet, Manon H. E., additional, Guan, Qinglin, additional, Zhao, Jianzhang, additional, Voronkova, Violeta K., additional, Escudero, Daniel, additional, Barbon, Antonio, additional, Xing, Yongheng, additional, Gurzadyan, Gagik G., additional, and Jacquemin, Denis, additional

Published
2021
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50. Singlet Fission, Polaron Formation, and Energy Transfer in Indolo[3,2-b]carbazole Thin Films and Single Crystals

Author

Zhao, Tongyu, Ni, Wenjun, Kloc, Christian, Sun, Licheng, Gurzadyan, Gagik G., Zhao, Tongyu, Ni, Wenjun, Kloc, Christian, Sun, Licheng, and Gurzadyan, Gagik G.

Abstract

The ultrafast excited-state relaxation dynamics of indolo[3,2-b]carbazole (ICZ) molecules were investigated in thin films and single crystals. In the ICZ film, singlet fission (SF) was directly observed both from the upper excited singlet states S-N within 480-850 fs and from the upper vibrational levels of the singlet state S-1 within 6-11 ps, which fully suppressed the intramolecular charge transfer (CT) process in S-1. In the ICZ crystal, the exciton relaxation through SF and polaron formation compete in the ultrafast timescale (<30 fs), which is accompanied by a thermally induced broadening of the S-1-S-N absorption band in the transient absorption spectra. The triplet-state lifetime is shortened from ICZ crystals (>1 ms) to films (2 mu s) due to SF with subsequent triplet-triplet annihilation, suggesting the impact of well-structured crystallinity and molecular packing on the exciton transport dynamics. The efficient SF together with well-characterized energy transfer and CT properties of ICZ solids extends the usage of ICZ-core-based organic materials in photovoltaic and electrochemical applications., QC 20210929

Published
2021
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