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Title: Static and time-resolved spectroscopic studies of low-symmetry Ru(II) polypyridyl complexes

Abstract

The spectroscopic and electrochemical properties of a series of four Ru{sup II} polypyridyl complexes are reported. Compounds of the form [Ru(dmb){sub x}(dea){sub 3{minus}x}]{sup 2+} (x = 0--3), where dmb is 4,4{prime}-dimethyl-2,2{prime}-bipyridine and dea is 4,4{prime}-bis(diethylamino)-2,2{prime}-bipyridine, have been prepared and studied using static and time-resolved electronic and vibrational spectroscopies as a prelude to femtosecond spectroscopic studies of excited-state dynamics. Static electronic spectra in CH{sub 3}CN solution reveal a systematic shift of the MLCT absorption envelope from a maximum of 458 nm in the case of [Ru(dmb){sub 3}]{sup 2+} to 518 nm for [Ru(dea){sub 3}]{sup 2+} with successive substitutions of dea for dmb, suggesting a dea-based chromophore as the lowest-energy species. However, analysis of static and time-resolved emission data indicates an energy gap ordering of [Ru(dmb){sub 3}]{sup 2+} > [Ru(dmb){sub 2}(dea)]{sup 2+} > [Ru(dea){sub 3}]{sup 2+} > [Ru(dmb)(DEA){sub 2}]{sup 2+}, at variance with the electronic structures inferred from the absorption spectra. Nanosecond time-resolved electronic absorption and time-resolved step-scan infrared data are used to resolve this apparent conflict and confirm localization of the long-lived {sup 3}MLCT state on dmb in all three complexes where this ligand is present, thus making the dea-based excited state unique to [Ru(dea){sub 3}]{sup 2+}. Electrochemical studies further revealmore » the origin of this result, where a strong influence of the dea ligand on the oxidative Ru{sup II/III} couple, due to {pi} donation from the diethylamino substituent, is observed. The electronic absorption spectra are then reexamined in light of the now well-determined excited-state electronic structure. The results serve to underscore the importance of complete characterization of the electronic structures of transition metal complexes before embarking on ultrafast studies of their excited-state properties.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of California, Berkeley, CA (US)
Sponsoring Org.:
USDOE; American Chemical Society
OSTI Identifier:
20000068
DOE Contract Number:  
FG03-96ER14665
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory
Additional Journal Information:
Journal Volume: 103; Journal Issue: 35; Other Information: PBD: 2 Sep 1999; Journal ID: ISSN 1089-5639
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; RUTHENIUM COMPLEXES; BIPYRIDINES; SYMMETRY; LIGANDS; OXIDATION; REDUCTION; SPECTROSCOPY; ELECTROCHEMISTRY; TRANSITION ELEMENT COMPLEXES

Citation Formats

Curtright, A.E., and McCusker, J.K. Static and time-resolved spectroscopic studies of low-symmetry Ru(II) polypyridyl complexes. United States: N. p., 1999. Web. doi:10.1021/jp9919415.
Curtright, A.E., & McCusker, J.K. Static and time-resolved spectroscopic studies of low-symmetry Ru(II) polypyridyl complexes. United States. doi:10.1021/jp9919415.
Curtright, A.E., and McCusker, J.K. Thu . "Static and time-resolved spectroscopic studies of low-symmetry Ru(II) polypyridyl complexes". United States. doi:10.1021/jp9919415.
@article{osti_20000068,
title = {Static and time-resolved spectroscopic studies of low-symmetry Ru(II) polypyridyl complexes},
author = {Curtright, A.E. and McCusker, J.K.},
abstractNote = {The spectroscopic and electrochemical properties of a series of four Ru{sup II} polypyridyl complexes are reported. Compounds of the form [Ru(dmb){sub x}(dea){sub 3{minus}x}]{sup 2+} (x = 0--3), where dmb is 4,4{prime}-dimethyl-2,2{prime}-bipyridine and dea is 4,4{prime}-bis(diethylamino)-2,2{prime}-bipyridine, have been prepared and studied using static and time-resolved electronic and vibrational spectroscopies as a prelude to femtosecond spectroscopic studies of excited-state dynamics. Static electronic spectra in CH{sub 3}CN solution reveal a systematic shift of the MLCT absorption envelope from a maximum of 458 nm in the case of [Ru(dmb){sub 3}]{sup 2+} to 518 nm for [Ru(dea){sub 3}]{sup 2+} with successive substitutions of dea for dmb, suggesting a dea-based chromophore as the lowest-energy species. However, analysis of static and time-resolved emission data indicates an energy gap ordering of [Ru(dmb){sub 3}]{sup 2+} > [Ru(dmb){sub 2}(dea)]{sup 2+} > [Ru(dea){sub 3}]{sup 2+} > [Ru(dmb)(DEA){sub 2}]{sup 2+}, at variance with the electronic structures inferred from the absorption spectra. Nanosecond time-resolved electronic absorption and time-resolved step-scan infrared data are used to resolve this apparent conflict and confirm localization of the long-lived {sup 3}MLCT state on dmb in all three complexes where this ligand is present, thus making the dea-based excited state unique to [Ru(dea){sub 3}]{sup 2+}. Electrochemical studies further reveal the origin of this result, where a strong influence of the dea ligand on the oxidative Ru{sup II/III} couple, due to {pi} donation from the diethylamino substituent, is observed. The electronic absorption spectra are then reexamined in light of the now well-determined excited-state electronic structure. The results serve to underscore the importance of complete characterization of the electronic structures of transition metal complexes before embarking on ultrafast studies of their excited-state properties.},
doi = {10.1021/jp9919415},
journal = {Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory},
issn = {1089-5639},
number = 35,
volume = 103,
place = {United States},
year = {1999},
month = {9}
}