Extended Near-Infrared Resonance Raman Investigations of an Organic Mixed-Valence System:  Diazatetracyclodiene Radical Cation

Abstract

Resonance Raman scattering studies in the extended near-infrared region show that six modes are coupled to the intramolecular charge-transfer transition in the mixed-valence radical cation diazatetracyclodiene. Spectral analysis based on time-dependent scattering theories shows that all six modes make substantial contributions to the vibrational reorganization energy. Measured Raman scattering cross sections were found to be considerably less than would be predicted by the conventional time-dependent scattering theories utilized here, evidently owing to complications arising from avoided surface crossings and anharmonic wave packet propagation. An examination of the classical and nonclassical kinetic effects of the coupled modes indicated that a considerable influence on the rate of intramolecular electron transfer is exerted by the modes collectively.

An anionic organic mixed-valence system with a remarkably well-resolved vibrational structure in its intervalence band

“…19 The three methods provide E op energies of 1.70, 1.30 and 1.50 eV that are in reasonable agreement with the experimental value of 1.35 eV, with the best match obtained at ZINDO level. The ZINDO estimates of 3.80 and 2.80 eV for the lowest energy absorption maxima of neutral 1 and dianion [1] 22 , respectively, are also in good agreement with the experimental data of 3.40 and 2.70 eV.…”

“…We also generated [1] 22 by addition of excess cobaltocene to 1 in CH 3 CN; the lowest energy feature (besides the weak and poorly resolved d-d transitions of excess cobaltocene 6 ) was a structured peak with a maximum at 459 nm. Addition of excess 1 to this solution led to the appearance of the structured bands at 920 and 491 nm, indicating that reduction to the dianion is chemically reversible and that the band at 459 nm is attributable to [1] 22 . This further supports the assignment of the 920 nm peak as the IVCT transition of [1] 2 .…”

“…Experimental mode-by-mode partition of the reorganisation energy has been previously derived from resonance Raman spectroscopy. 22 The total reorganisation energy of 0.180 eV can be compared to values of 0.21-0.26 eV estimated for another similarly bridged species, the N,N,NA,NA-tetrakis(p-methoxyphenyl)-p-phenylenediamine cation. 21 In summary, [1] 2 is a class-III organic MV species with a larger H AB than anionic examples of comparable bridge length.…”

Organic Mixed‐Valence Compounds: A Playground for Electrons and Holes

“…Furthermore, the bis(hydrazyl) MV systems were studied in detail by resonance Raman spectroscopy, which allows identification of the active modes that participate in the resonant excitation, which, in the case of MV compounds, is associated with the charge-transfer event. [171] An excitation in the NIR region at 1064 nm directly into the IV-CT transition of MV compound 15 + shows that the averaged vibrational modeñ v = 1100 cm À1 is mainly composed of six modes, where the N=N stretching modes are most important. The high value ofñ v as well as the small inner reorganization energy l v together cause a small Huang-Rhys factor S [see Eq.…”

Organische gemischtvalente Verbindungen: ein Spielplatz für Elektronen und Löcher

“…Dies erlaubt die Identifizierung aktiver Moden, die an der Resonanzanregung beteiligt und die im Fall der MVVerbindungen mit dem Ladungstransfer assoziiert sind. [171] Eine Anregung im NIR-Bereich bei 1064 nm direkt in den IV-CT-Übergang zeigt für Verbindung 15 …”