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Title: Photoinduced energy transfer in transition metal complex oligomers

Abstract

The work we have done over the past three years has been directed toward the preparation, characterization and photophysical examination of mono- and bimetallic diimine complexes. The work is part of a broader project directed toward the development of stable, efficient, light harvesting arrays of transition metal complex chromophores. One focus has been the synthesis of rigid bis-bidentate and bis-tridentate bridging ligands. We have managed to make the ligand bphb in multigram quantities from inexpensive starting materials. The synthetic approach used has allowed us prepare a variety of other ligands which may have unique applications (vide infra). We have prepared, characterized and examined the photophysical behavior of Ru(II) and Re(I) complexes of the ligands. Energy donor/acceptor complexes of bphb have been prepared which exhibit nearly activationless energy transfer. Complexes of Ru(II) and Re(I) have also been prepared with other polyunsaturated ligands in which two different long lived ( > 50 ns) excited states exist; results of luminescence and transient absorbance measurements suggest the two states are metal-to-ligand charge transfer and ligand localized {pi}{r_arrow}{pi}* triplets. Finally, we have developed methods to prepare polymetallic complexes which are covalently bound to various surfaces. The long term objective of this work is to makemore » light harvesting arrays for the sensitization of large band gap semiconductors. Details of this work are provided in the body of the report.« less

Publication Date:
Research Org.:
Tulane Univ., New Orleans, LA (United States)
Sponsoring Org.:
USDOE Office of Energy Research, Washington, DC (United States)
OSTI Identifier:
464184
Report Number(s):
DOE/ER/14309-T1
ON: DE97005234; TRN: 97:002689
DOE Contract Number:
FG05-92ER14309
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: [1997]
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; RUTHENIUM COMPLEXES; ENERGY TRANSFER; LUMINESCENCE; RHENIUM COMPLEXES; LIGANDS; BIPYRIDINES; SPECTROSCOPY; PHOSPHONATES; PHOSPHONIC ACIDS; DISSOCIATION; EXCITED STATES; MOLECULAR STRUCTURE; STRUCTURAL MODELS; PHOTOCHEMICAL REACTIONS

Citation Formats

NONE. Photoinduced energy transfer in transition metal complex oligomers. United States: N. p., 1997. Web. doi:10.2172/464184.
NONE. Photoinduced energy transfer in transition metal complex oligomers. United States. doi:10.2172/464184.
NONE. Tue . "Photoinduced energy transfer in transition metal complex oligomers". United States. doi:10.2172/464184. https://www.osti.gov/servlets/purl/464184.
@article{osti_464184,
title = {Photoinduced energy transfer in transition metal complex oligomers},
author = {NONE},
abstractNote = {The work we have done over the past three years has been directed toward the preparation, characterization and photophysical examination of mono- and bimetallic diimine complexes. The work is part of a broader project directed toward the development of stable, efficient, light harvesting arrays of transition metal complex chromophores. One focus has been the synthesis of rigid bis-bidentate and bis-tridentate bridging ligands. We have managed to make the ligand bphb in multigram quantities from inexpensive starting materials. The synthetic approach used has allowed us prepare a variety of other ligands which may have unique applications (vide infra). We have prepared, characterized and examined the photophysical behavior of Ru(II) and Re(I) complexes of the ligands. Energy donor/acceptor complexes of bphb have been prepared which exhibit nearly activationless energy transfer. Complexes of Ru(II) and Re(I) have also been prepared with other polyunsaturated ligands in which two different long lived ( > 50 ns) excited states exist; results of luminescence and transient absorbance measurements suggest the two states are metal-to-ligand charge transfer and ligand localized {pi}{r_arrow}{pi}* triplets. Finally, we have developed methods to prepare polymetallic complexes which are covalently bound to various surfaces. The long term objective of this work is to make light harvesting arrays for the sensitization of large band gap semiconductors. Details of this work are provided in the body of the report.},
doi = {10.2172/464184},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 01 00:00:00 EST 1997},
month = {Tue Apr 01 00:00:00 EST 1997}
}

Technical Report:

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  • The work done over the past three years has been directed toward the preparation, characterization and photophysical examination of mono- and bimetallic diimine complexes. The work is part of a broader project directed toward the development of stable, efficient, light harvesting arrays of transition metal complex chromophores. One focus has been the synthesis of rigid bis-bidentate and bis-tridentate bridging ligands. The authors have managed to make the ligand bphb in multigram quantities from inexpensive starting materials. The synthetic approach used has allowed them to prepare a variety of other ligands which may have unique applications (vide infra). They have prepared,more » characterized and examined the photophysical behavior of Ru(II) and Re(I) complexes of the ligands. Energy donor/acceptor complexes of bphb have been prepared which exhibit nearly activationless energy transfer. Complexes of Ru(II) and Re(I) have also been prepared with other polyunsaturated ligands in which two different long lived (> 50 ns) excited states exist; results of luminescence and transient absorbance measurements suggest the two states are metal-to-ligand charge transfer and ligand localized {pi}{r_arrow}{pi}* triplets. Finally, the authors have developed methods to prepare polymetallic complexes which are covalently bound to various surfaces. The long term objective of this work is to make light harvesting arrays for the sensitization of large band gap semiconductors. Details of this work are provided in the body of the report.« less
  • Excited-state relaxation pathways have been examined for some bi- and trinuclear transition-metal complexes containing the Ru(bpy){sub 2}{sup 2+} chromophore linked (or metalated) through cyanide to an amine chromium(III) or rhodium(III) complex. The ({sup 3}CT)Ru(bpy){sub 2}{sup 2+} absorption and emission maxima and the Ru(III)-(II) reduction potentials all increase in energy with metalation. In most instances energy migration from the initially excited ruthenium center to the acceptor metal centers occurred in discrete steps analogous to elementary chemical reactions between independent molecular species.The migration of energy was manifested by quenching of the ({sup 3}CT)Ru donor emission. This was sometimes accompanied either by ({supmore » 2}E)Cr(III) phosphorescence emission in the chromium metalates or by the growth of a metal-to-metal charge-transfer absorption in a rhodium metalate. Picosecond flash photolysis has been used to observe the equilibration (in about 1 ns) between the ({sup 3}CT)Ru(bpy){sub 2}{sup 2+} and the triplet ligand field excited states of Rh(NH{sub 3}){sub 5}{sup 3+}.« less
  • This program is interested in absorbing energy in one portion of a polymetallic complex, transferring that energy to another portion of the molecule, and allowing this remote center to undergo a desired chemical reaction. One advantage of this intramolecular energy transfer process over the more common intermolecular processes is that the inherent inefficiencies of bimolecular collisional processes can be circumvented. Another advantage is that coupling of more than one metal fragment into one complex, each fragment having different properties, (i.e., light absorbing, reacting, etc.) allows the ultimate flexibility in the design of the overall system. The results contained in thismore » report deal with our progress in developing intramolecular energy transfer systems. We have divided up the reactant molecules into three component parts, the antenna fragment (highly absorbing metal center), the reactive fragment (center that undergoes reaction), and the bridge (ligand that connects and couples the two metal centers. Most of the systems studied contain the bridging ligand 2,2'-bipyrimidine, which functions as a chelate to both the antenna and reactive fragment. This bridging system has the advantages that it maintains the integrity of the polymetallic systems and is very effective in electronically coupling the metal centers to each other. The photochemistry of some metal dihydrido reactive fragments is added to the previous information obtained on a series of antenna fragments.« less
  • The polymetallic systems involving 2,2'-bipyridine (bpm) have shown only one breakthrough in the previous twelve-month period. We have, however, been successful with one such synthetic procedure in that we have recently prepared (bpy)/sub 2/Ru(bpm)Rh(PPh/sub 3/)/sub 2/H/sub 2//sup 3 +/. An additional study involved systems in which bpm is bridged to tetracyanoferrate units. Because of the difficulty in deprotonating 2,2'-biimidazole and 2,2'-bibenzenebiimidazole, we have discontinued work with these anionic ligands. We are attempting to prepare the 4,4',5,5'-tetracyano derivative which should undergo more facile deprotonation and supply a good di-negatively charged bridging ligand. We have experienced a substantial progress in the proposedmore » research using 2,3-bis(2'-pyridyl)pyrazine as a bridging ligand. This ligand has been used to couple Ru(II) units to form L/sub 2/Ru(dpp)RuL'/sup 4 +/ units L = bpy or phen, to couple Fe(II) units to form (Fe(CN)/sub 4/)/sub 2/dpp/sup 2 +/ and to couple the heterometallic system, (bpy)/sub 2/RudppFe(CN)/sub 4/. These systems show extensive metal-metal coupling through electrochemical studies, emission maxima that depend upon the M(dpp)M' linkage, and lifetimes in the 50 to 200 ns region in acetonitrile at room temperature.« less
  • The ability of transition metal complexes to absorb visible radiation makes these series of compounds very desirable for energy conversion reactions. Our approach to this area of chemistry has not followed the exact same line as others in the area. Specifically, we are interested in absorbing energy in one portion of a polymetallic complex, transferring that energy to another portion of the molecule, and allowing this remote center to undergo a desired chemical reaction. One advantage of this intramolecular energy transfer process over the more common intermolecular processes is that the inherent inefficiencies of bimolecular collisional processes can be circumvented.more » Another advantage is that coupling of more than one metal fragment into one complex, each fragment having different properties (i.e., light absorbing, reacting), allows the ultimate flexibility in the design of the overall system. The results contained in this report deal with our progress in developing intramolecular energy transfer systems.« less