Characterization of infrared vibrational activity in specific totally symmetric bridging modes of mixed-valence systems near the localized-to-delocalized transition

Rocha, Reginaldo C.; Shreve, Andrew P.

doi:10.1016/j.chemphys.2006.01.008

Cited by 16 publications

(20 citation statements)

References 33 publications

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“…Intensified IR bands have previously been reported for conjugated polymer polarons 33 , 43 − 47 and mixed-valence compounds, 48 , 49 and they are often described as “infra-red active vibrations” (IRAVs). They can arise from both charge localization, signifying Robin–Day class II/III borderline character, 49 and from vibronic coupling to low-energy electronic transitions, even in fully delocalized (class III) systems. 48 , 49 Charge localization reduces the symmetry of a molecule, making Raman modes become IR-active and amplifying IR bands.…”

Section: Resultsmentioning

confidence: 99%

Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires

et al. 2017

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The radical cations of a family of π-conjugated porphyrin arrays have been investigated: linear chains of N = 1–6 porphyrins, a 6-porphyrin nanoring and a 12-porphyrin nanotube. The radical cations were generated in solution by chemical and electrochemical oxidation, and probed by vis–NIR–IR and EPR spectroscopies. The cations exhibit strong NIR bands at ∼1000 nm and 2000–5000 nm, which shift to longer wavelength with increasing oligomer length. Analysis of the NIR and IR spectra indicates that the polaron is delocalized over 2–3 porphyrin units in the linear oligomers. Some of the IR vibrational bands are strongly intensified on oxidation, and Fano-type antiresonances are observed when activated vibrations overlap with electronic transitions. The solution-phase EPR spectra of the radical cations have Gaussian lineshapes with linewidths proportional to N–0.5, demonstrating that at room temperature the spin hops rapidly over the whole chain on the time scale of the hyperfine coupling (ca. 100 ns). Direct measurement of the hyperfine couplings through electron–nuclear double resonance (ENDOR) in frozen solution (80 K) indicates distribution of the spin over 2–3 porphyrin units for all the oligomers, except the 12-porphyrin nanotube, in which the spin is spread over about 4–6 porphyrins. These experimental studies of linear and cyclic cations give a consistent picture, which is supported by DFT calculations and multiparabolic modeling with a reorganization energy of 1400–2000 cm–1 and coupling of 2000 cm–1 for charge transfer between neighboring sites, placing the system in the Robin–Day class III.

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Section: Resultsmentioning

confidence: 99%

Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires

et al. 2017

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“…The vibronic enhancement of normally forbidden IR transitions is distinctly different from the use of the 8a mode as a marker for localization of charge on the time scale longer than the period of the mode, ca. 20 fs [23,56]. IR activity of symmetric pyrazine modes exists in the full IR spectra for mixed-valence anions 4 − -6 − , but the active 8a mode (the most intense of these bands) in particular is overlapped with cluster acetate bands and is not unambiguously clear.…”

Section: If the Bridge Is Rocking The Ir Can Be Shockingmentioning

confidence: 95%

Inter- or intramolecular electron transfer between triruthenium clusters: we’ll cross that bridge when we come to it

Glover

Goeltz

Lear

et al. 2010

Coordination Chemistry Reviews

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“…For this band, 3Z2600 M K1 cm K1 compared with 3Z800 M K1 cm K1 in cis-[Os(bpy) 2 (pz)Cl] C . This appears to be a non-Condon effect with coupling of the vibration to intervalence transfer across the bridge (Demadis et al 1998a(Demadis et al ,b, 1999aRocha & Shreve 2004, 2006.…”

Section: (I) Symmetrical Vibrations In the Bridgementioning

confidence: 99%

“…For harmonic oscillator vibrational wave functions, the contribution to the barrier through the vZ0/vZ0 channel is exp(KS )(S v /v!). (Demadis et al 1998a(Demadis et al ,b, 1999aRocha & Shreve 2004, 2006 (Lu et al 1995).…”

Section: (Iii) Barrier Vibrationsmentioning

confidence: 99%

“…An example is shown in figure 4 in the n(bpy) ring-stretching region for [(bpy) 2 ClOs(BL)OsCl(bpy) 2 ] 2C/3C/4C (BLZpz and 4,4 0 -bpy). The spectrum of [(bpy) 2 ClOs(4,4 0 -bpy)OsCl(bpy) 2 ] 3C is the sum of spectra for Os(III) and Os(II) with shifts of 5-7 cm K1 providing direct evidence for an asymmetric electronic distribution and localized oxidation states (Demadis et al 1998a(Demadis et al ,b, 1999aRocha & Shreve 2004, 2006. By contrast, the n(bpy) spectrum of [(bpy) 2 ClOs(pz)OsCl(bpy) 2 ] 3C is the average of those of Os(III) and Os(II) with bands appearing at 1316, 1423, 1450, 1465 and 1487 cm K1 .…”

Section: (Ii) Spectator Vibrationsmentioning

confidence: 99%

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Probing the localized-to-delocalized transition

Concepcion

Dattelbaum

Meyer

et al. 2007

Phil. Trans. R. Soc. A.

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Detailed understanding of the transition between localized and delocalized behaviour in mixed valence compounds has been elusive as evidenced by many interpretations of the Creutz-Taube ion, [(NH 3 ) 5 Ru(pz)Ru(NH 3 ) 5 ] 5C . In a review in 2001, experimental protocols and a systematic model to probe this region were proposed and applied to examples in the literature. The model included: (i) multiple orbital interactions in ligand-bridged transition metal complexes, (ii) inclusion of spin-orbit coupling which, for dp 5 -dp 6 complexes, leads to five low-energy bands, two from interconfigurational (dp/dp) transitions at the dp 5 site and three from intervalence transfer transitions, (iii) differences in time scale between coupled vibrations and solvent modes which can result in solvent averaging with continued electronic asymmetry defining 'class II-III', an addition to the Robin-Day classification scheme, and (iv) delineation of coupled vibrations into barrier vibrations and 'spectator' vibrations. The latter provide direct insight into localization or delocalization and time scales for electron transfer. In this paper, the earlier model is applied to a series of mixed-valence molecules.

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Characterization of infrared vibrational activity in specific totally symmetric bridging modes of mixed-valence systems near the localized-to-delocalized transition

Cited by 16 publications

References 33 publications

Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires

Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires

Inter- or intramolecular electron transfer between triruthenium clusters: we’ll cross that bridge when we come to it

Probing the localized-to-delocalized transition

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