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Title: Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution

Abstract

Ultrafast excited state structural dynamics of [Cu{sup I}(dmp){sub 2}]{sup +} (dmp = 2,9-dimethyl-1,10-phenanthroline) have been studied to identify structural origins of transient spectroscopic changes during the photoinduced metal-to-ligand-charge-transfer (MLCT) transition that induces an electronic configuration change from Cu(I) (3d{sup 10}) to Cu(II) (3d{sup 9}). This study has important connections with the flattening of the Franck-Condon state tetrahedral geometry and the ligation of Cu(II)* with the solvent observed in the thermally equilibrated MLCT state by our previous laser-initiated time-resolved x-ray absorption spectroscopy (LITR-XAS) results. To better understand the structural photodynamics of Cu(I) complexes, we have studied both [Cu{sup I}(dmp){sub 2}]{sup +} and [Cu{sup I}(dpp){sub 2}]{sup +} (dpp = 2,9-diphenyl-1,10-phenanthroline) in solvents with different dielectric constants, viscosities and thermal diffusivities by transient absorption spectroscopy. The observed spectral dynamics suggest that a solvent-independent inner-sphere relaxation process is occurring despite the large amplitude motions due to the flattening of the tetrahedral coordinated geometry. The singlet fluorescence dynamics of photoexcited [Cu{sup I}(dmp){sub 2}]{sup +} were measured in the coordinating solvent acetonitrile, using the fluorescence upconversion method at different emission wavelengths. At the bluest emission wavelengths, a prompt fluorescence lifetime of 66 fs is attributed to the excited state deactivation processes due to the internal conversionmore » and intersystem crossing at the Franck-Condon state geometry. The differentiation between the prompt fluorescence lifetime with the tetrahedral Franck-Condon geometry and that with the flattened tetrahedral geometry uncovers an unexpected ultrafast flattening process in the MLCT state of [Cu{sup I}(dmp){sub 2}]{sup +}. These results provide guidance for future x-ray structural studies on ultrafast time scale, as well as for synthesis towards its applications in solar energy conversion.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
902226
Report Number(s):
UCRL-JRNL-225105
Journal ID: ISSN 0002-7863; JACSAT; TRN: US200717%%207
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 129; Journal Issue: 7; Journal ID: ISSN 0002-7863
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; ACETONITRILE; AMPLITUDES; CONFIGURATION; DEACTIVATION; EXCITED STATES; FLUORESCENCE; GEOMETRY; INTERNAL CONVERSION; LIFETIME; PERMITTIVITY; RELAXATION; SOLAR ENERGY CONVERSION; SOLVENTS; SYNTHESIS; TRANSIENTS; WAVELENGTHS

Citation Formats

Shaw, G B, Grant, C D, Shirota, H, Castner, Jr, E W, Meyer, G J, and Chen, L X. Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution. United States: N. p., 2006. Web.
Shaw, G B, Grant, C D, Shirota, H, Castner, Jr, E W, Meyer, G J, & Chen, L X. Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution. United States.
Shaw, G B, Grant, C D, Shirota, H, Castner, Jr, E W, Meyer, G J, and Chen, L X. 2006. "Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution". United States. https://www.osti.gov/servlets/purl/902226.
@article{osti_902226,
title = {Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution},
author = {Shaw, G B and Grant, C D and Shirota, H and Castner, Jr, E W and Meyer, G J and Chen, L X},
abstractNote = {Ultrafast excited state structural dynamics of [Cu{sup I}(dmp){sub 2}]{sup +} (dmp = 2,9-dimethyl-1,10-phenanthroline) have been studied to identify structural origins of transient spectroscopic changes during the photoinduced metal-to-ligand-charge-transfer (MLCT) transition that induces an electronic configuration change from Cu(I) (3d{sup 10}) to Cu(II) (3d{sup 9}). This study has important connections with the flattening of the Franck-Condon state tetrahedral geometry and the ligation of Cu(II)* with the solvent observed in the thermally equilibrated MLCT state by our previous laser-initiated time-resolved x-ray absorption spectroscopy (LITR-XAS) results. To better understand the structural photodynamics of Cu(I) complexes, we have studied both [Cu{sup I}(dmp){sub 2}]{sup +} and [Cu{sup I}(dpp){sub 2}]{sup +} (dpp = 2,9-diphenyl-1,10-phenanthroline) in solvents with different dielectric constants, viscosities and thermal diffusivities by transient absorption spectroscopy. The observed spectral dynamics suggest that a solvent-independent inner-sphere relaxation process is occurring despite the large amplitude motions due to the flattening of the tetrahedral coordinated geometry. The singlet fluorescence dynamics of photoexcited [Cu{sup I}(dmp){sub 2}]{sup +} were measured in the coordinating solvent acetonitrile, using the fluorescence upconversion method at different emission wavelengths. At the bluest emission wavelengths, a prompt fluorescence lifetime of 66 fs is attributed to the excited state deactivation processes due to the internal conversion and intersystem crossing at the Franck-Condon state geometry. The differentiation between the prompt fluorescence lifetime with the tetrahedral Franck-Condon geometry and that with the flattened tetrahedral geometry uncovers an unexpected ultrafast flattening process in the MLCT state of [Cu{sup I}(dmp){sub 2}]{sup +}. These results provide guidance for future x-ray structural studies on ultrafast time scale, as well as for synthesis towards its applications in solar energy conversion.},
doi = {},
url = {https://www.osti.gov/biblio/902226}, journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 7,
volume = 129,
place = {United States},
year = {Thu Oct 05 00:00:00 EDT 2006},
month = {Thu Oct 05 00:00:00 EDT 2006}
}