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Title: Modulating the Light Switch by [superscript 3]MLCT-[superscript 3]pi pi* State Interconversion

Abstract

The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: {lambda}{sub max} = 393 nm) upon substitution at the terminal phenyl groups (2: {lambda}{sub max} = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at {lambda}{sub max} = 450 nm are observed for [Ru(phen){sub 2}bptt]{sup 2+}(3) and [Ru(phen){sub 2}tbptt]{sup 2+}(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy){sub 3}]{sup 2+} and [Ru(phen){sub 3}]{sup 2+}, indicating that the MLCT excited state is primarily localized within the [Ru(phen){sub 3}]{sup 2+} manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: {phi}H{sub 2}O = 0.005, 4: {phi}H{sub 2}O = 0.011) and biexponential decay kinetics (3: {tau}{submore » 1} = 40 ns, {tau}{sub 2} = 230 ns; 4: {tau}{sub 1} {approx} 26 ns, {tau}{sub 2} = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield ({phi}DNA = 0.045), while the quantum yield of 4 is relatively unaffected ({phi}DNA = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K{sub b} = 3.3 x 10{sup 4} M{sup -1}). The origin of this light switch behavior involves two competing {sup 3}MLCT states similar to that of the extensively studied light switch molecule [Ru(phen){sub 2}dppz]{sup 2+}. The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the {sup 3}{pi}{pi}* excited state into competition with the emitting {sup 3}MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.« less

Authors:
; ; ; ;  [1]
  1. Indiana
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1029000
Resource Type:
Journal Article
Journal Name:
Inorg. Chem.
Additional Journal Information:
Journal Volume: 49; Journal Issue: (24) ; 12, 2010; Journal ID: ISSN 0020-1669
Country of Publication:
United States
Language:
ENGLISH
Subject:
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AQUEOUS SOLUTIONS; CLATHRATES; DECAY; DNA; ELECTRONIC STRUCTURE; ETHANOL; EXCITED STATES; KINETICS; LUMINESCENCE; ORIGIN; RED SHIFT; RUTHENIUM; RUTHENIUM COMPLEXES; TEMPERATURE DEPENDENCE

Citation Formats

Spencer, Brigitte R, Kraft, Brian J, Hughes, Chris G, Pink, Maren, and Zaleski, Jeffrey M. Modulating the Light Switch by [superscript 3]MLCT-[superscript 3]pi pi* State Interconversion. United States: N. p., 2012. Web. doi:10.1021/ic1011617.
Spencer, Brigitte R, Kraft, Brian J, Hughes, Chris G, Pink, Maren, & Zaleski, Jeffrey M. Modulating the Light Switch by [superscript 3]MLCT-[superscript 3]pi pi* State Interconversion. United States. https://doi.org/10.1021/ic1011617
Spencer, Brigitte R, Kraft, Brian J, Hughes, Chris G, Pink, Maren, and Zaleski, Jeffrey M. Fri . "Modulating the Light Switch by [superscript 3]MLCT-[superscript 3]pi pi* State Interconversion". United States. https://doi.org/10.1021/ic1011617.
@article{osti_1029000,
title = {Modulating the Light Switch by [superscript 3]MLCT-[superscript 3]pi pi* State Interconversion},
author = {Spencer, Brigitte R and Kraft, Brian J and Hughes, Chris G and Pink, Maren and Zaleski, Jeffrey M},
abstractNote = {The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: {lambda}{sub max} = 393 nm) upon substitution at the terminal phenyl groups (2: {lambda}{sub max} = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at {lambda}{sub max} = 450 nm are observed for [Ru(phen){sub 2}bptt]{sup 2+}(3) and [Ru(phen){sub 2}tbptt]{sup 2+}(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy){sub 3}]{sup 2+} and [Ru(phen){sub 3}]{sup 2+}, indicating that the MLCT excited state is primarily localized within the [Ru(phen){sub 3}]{sup 2+} manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: {phi}H{sub 2}O = 0.005, 4: {phi}H{sub 2}O = 0.011) and biexponential decay kinetics (3: {tau}{sub 1} = 40 ns, {tau}{sub 2} = 230 ns; 4: {tau}{sub 1} {approx} 26 ns, {tau}{sub 2} = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield ({phi}DNA = 0.045), while the quantum yield of 4 is relatively unaffected ({phi}DNA = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K{sub b} = 3.3 x 10{sup 4} M{sup -1}). The origin of this light switch behavior involves two competing {sup 3}MLCT states similar to that of the extensively studied light switch molecule [Ru(phen){sub 2}dppz]{sup 2+}. The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the {sup 3}{pi}{pi}* excited state into competition with the emitting {sup 3}MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.},
doi = {10.1021/ic1011617},
url = {https://www.osti.gov/biblio/1029000}, journal = {Inorg. Chem.},
issn = {0020-1669},
number = (24) ; 12, 2010,
volume = 49,
place = {United States},
year = {2012},
month = {1}
}