A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II)

Leif Hammarström, Francesco Barigelletti, Lucia Flamigni, Maria Teresa Indelli, Nicola Armaroli, Giuseppe Calogero, Massimo Guardigli, Angelique Sour, Jean Paul Collin, Jean Pierre Sauvage

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Abstract

For the structurally rigid homometallic dinuclear complexes (ttp)Ru(tpy-tpy)Ru(ttp)4+ and (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, we have obtained ground-state absorption spectra and transient-absorption difference spectra at room temperature and luminescence spectra and lifetimes in the temperature interval from room temperature to the rigid matrix (90 K); the solvent was acetonitrile or butyronitrile (tpy is 2,27prime;:6′,2″-terpyridine, ttp is 4′-p-tolyl-2,2′:6′,2″-tpy, and ph is 1,4-phenylene). The gathered spectroscopic data indicate that after absorption of visible light, formation of the luminescent metal-to-ligand charge transfer (MLCT) excited states takes place, which involves the bridging ligand (BL). Since we found that (ttp)Ru(tpy-tpy)Ru(ttp)4+ is a good luminophore (λmax = 720 nm, Φ = 4.7 x 10-3, and τ = 570 ns) while both (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+max = 656 nm, Φ = 1.1 x 10-4, and τ = 4 ns) and the reference mononuclear complex Ru(ttp)2 2+max = 640 nm, Φ = 3.2 x 10-5, and τ = 0.9 ns) are not, we have explored the effects brought about by the delocalization and energy content of the luminescent state. The study of the temperature dependence of the luminescence lifetimes indicates that two main nonradiative paths, i and ii, are responsible for deactivation of the luminescent state. Path i directly connects the luminescent and ground states; within the frame of the "energy-gap law", vibronic analysis of low-temperature luminescence profiles enables one to correlate the delocalization of the M → BL CT state and the extent of structural distortions occurring at the accepting ligand. Thermally activated decay via a metal-centered (MC, of dd orbital origin) excited state characterizes path ii, with a MLCT - MC energy separation ΔE = 3800, 2300, and 1600 cm-1 for (ttp)Ru(tpy-tpy)Ru-(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(ttp)2 2+, respectively. At room temperature, for this limited series of complexes it is found that nonradiative processes governed by the "energy-gap law" play a minor role as compared to thermally activated processes, the ratios of the rate constants being knr act/knr dir ≈ 16, 1900, and 7000 for (ttp)Ru(tpy-tpy)Ru(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(Up)2 2+, respectively.

Original languageEnglish
Pages (from-to)9061-9069
Number of pages9
JournalJournal of Physical Chemistry A
Volume101
Issue number48
Publication statusPublished - Nov 27 1997

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Ruthenium
Excited states
ruthenium
Charge transfer
Metals
charge transfer
Ligands
ligands
metals
excitation
Luminescence
luminescence
room temperature
Temperature
Ground state
Energy gap
life (durability)
ground state
deactivation
acetonitrile

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Hammarström, L., Barigelletti, F., Flamigni, L., Indelli, M. T., Armaroli, N., Calogero, G., ... Sauvage, J. P. (1997). A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II). Journal of Physical Chemistry A, 101(48), 9061-9069.

A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II). / Hammarström, Leif; Barigelletti, Francesco; Flamigni, Lucia; Indelli, Maria Teresa; Armaroli, Nicola; Calogero, Giuseppe; Guardigli, Massimo; Sour, Angelique; Collin, Jean Paul; Sauvage, Jean Pierre.

In: Journal of Physical Chemistry A, Vol. 101, No. 48, 27.11.1997, p. 9061-9069.

Research output: Contribution to journalArticle

Hammarström, L, Barigelletti, F, Flamigni, L, Indelli, MT, Armaroli, N, Calogero, G, Guardigli, M, Sour, A, Collin, JP & Sauvage, JP 1997, 'A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II)', Journal of Physical Chemistry A, vol. 101, no. 48, pp. 9061-9069.
Hammarström, Leif ; Barigelletti, Francesco ; Flamigni, Lucia ; Indelli, Maria Teresa ; Armaroli, Nicola ; Calogero, Giuseppe ; Guardigli, Massimo ; Sour, Angelique ; Collin, Jean Paul ; Sauvage, Jean Pierre. / A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II). In: Journal of Physical Chemistry A. 1997 ; Vol. 101, No. 48. pp. 9061-9069.
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T1 - A study on delocalization of MLCT excited states by rigid bridging ligands in homometallic dinuclear complexes of ruthenium(II)

AU - Hammarström, Leif

AU - Barigelletti, Francesco

AU - Flamigni, Lucia

AU - Indelli, Maria Teresa

AU - Armaroli, Nicola

AU - Calogero, Giuseppe

AU - Guardigli, Massimo

AU - Sour, Angelique

AU - Collin, Jean Paul

AU - Sauvage, Jean Pierre

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N2 - For the structurally rigid homometallic dinuclear complexes (ttp)Ru(tpy-tpy)Ru(ttp)4+ and (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, we have obtained ground-state absorption spectra and transient-absorption difference spectra at room temperature and luminescence spectra and lifetimes in the temperature interval from room temperature to the rigid matrix (90 K); the solvent was acetonitrile or butyronitrile (tpy is 2,27prime;:6′,2″-terpyridine, ttp is 4′-p-tolyl-2,2′:6′,2″-tpy, and ph is 1,4-phenylene). The gathered spectroscopic data indicate that after absorption of visible light, formation of the luminescent metal-to-ligand charge transfer (MLCT) excited states takes place, which involves the bridging ligand (BL). Since we found that (ttp)Ru(tpy-tpy)Ru(ttp)4+ is a good luminophore (λmax = 720 nm, Φ = 4.7 x 10-3, and τ = 570 ns) while both (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+ (λmax = 656 nm, Φ = 1.1 x 10-4, and τ = 4 ns) and the reference mononuclear complex Ru(ttp)2 2+ (λmax = 640 nm, Φ = 3.2 x 10-5, and τ = 0.9 ns) are not, we have explored the effects brought about by the delocalization and energy content of the luminescent state. The study of the temperature dependence of the luminescence lifetimes indicates that two main nonradiative paths, i and ii, are responsible for deactivation of the luminescent state. Path i directly connects the luminescent and ground states; within the frame of the "energy-gap law", vibronic analysis of low-temperature luminescence profiles enables one to correlate the delocalization of the M → BL CT state and the extent of structural distortions occurring at the accepting ligand. Thermally activated decay via a metal-centered (MC, of dd orbital origin) excited state characterizes path ii, with a MLCT - MC energy separation ΔE = 3800, 2300, and 1600 cm-1 for (ttp)Ru(tpy-tpy)Ru-(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(ttp)2 2+, respectively. At room temperature, for this limited series of complexes it is found that nonradiative processes governed by the "energy-gap law" play a minor role as compared to thermally activated processes, the ratios of the rate constants being knr act/knr dir ≈ 16, 1900, and 7000 for (ttp)Ru(tpy-tpy)Ru(ttp)4+, (ttp)Ru(tpy-ph-tpy)Ru(ttp)4+, and Ru(Up)2 2+, respectively.

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