Computational and spectroscopic studies of organic mixed-valence compounds: where is the charge?

Abstract

This article discusses recent progress by a combination of spectroscopy and quantum-chemical calculations in classifying and characterizing organic mixed-valence systems in terms of their localized vs. delocalized character. A recently developed quantum-chemical protocol based on non-standard hybrid functionals and continuum solvent models is evaluated for an extended set of mixed-valence bis-triarylamine radical cations, augmented by unsymmetrical neutral triarylamine-perchlorotriphenylmethyl radicals. It turns out that the protocol is able to provide a successful assignment to class II or class III Robin-Day behavior and gives quite accurate ground-and excited-state properties for the radical cations. The limits of the protocol are probed by the anthracene-bridged system 8, where it is suspected that specific solute-solvent interactions are important and not covered by the continuum solvent model. Intervalence charge-transfer excitation energies for the neutral unsymmetrical radicals are systematically overestimated, but dipole moments and a number of other properties are obtained accurately by the protocol.

Organische gemischtvalente Verbindungen: ein Spielplatz für Elektronen und Löcher

“…[117,133,146] Kürzlich umgingen M. Kaupp et al dieses Problem, indem sie den Anteil an exaktem HF-Austausch in Hybrid-Dichtefunktionalmethoden so anpassten, dass das Grenzverhalten an der Klasse II zu Klasse III bei Bis(triarylamin)-Radikalkationen richtig wiedergegeben wird. [147,272] 2.8. Einfluss geometrischer Faktoren auf die elektronische Kopplung und die ET-Geschwindigkeitskonstante…”

Mixed‐Valence Ruthenium Complexes Rotating through a Conformational Robin–Day Continuum

“…Such a protocol (see Computational Details) has recently been introduced for organic MV systems, where it has allowed valid descriptions close to the class II -class III borderline for a wide variety of MV systems and solvent environments. [18][19][20][21][22] Still more recently, it has been extended to applications in the modeling of ET processes in transition-metal MV systems. [17,23] However, regardless of the computational methodology employed, any interpretation of quantum-chemical results based on a single, static, lowest-energy molecular structure will not accurately model systems in which molecular dynamics play an important role on the optoelectronic properties of a molecule.…”

“…For selected cases, additional single-point TDDFT calculations were carried out using the Gaussian09 code, [31] which features a somewhat different treatment of the solvent model for excitations. [20] The computational protocol used, which has been developed specifically to provide accurate ground-and excited-state properties for organic [18][19][20][21][22] and transition-metal [17,23] mixed-valence systems, is based on the adjusted global hybrid functional BLYP35, [21] …”

“…[17] The identification of these conformational factors prompt reconsideration of other ligand-bridged bimetallic mixedvalence complexes [M-bridge-M] + in which d-π-d overlap along the molecular backbone can be anticipated to be strongly dependent on the relative orientation of the constituent fragments. A quantum-chemical methodology that gives a faithful description of localization/delocalization (see below), [17][18][19][20][21][22][23] has been used here to reconsider the description of three formally mixed-valence bimetallic ruthenium complexes for which a wealth of experimental data has been accumulated (Chart 1 [2] + both contain the 1,4-diethynylbenzene (µ-C≡CC 6 H 4 C≡C) bridge but differ in the composition of the supporting ligands, and in both cases, conflicting evidence exists regarding the MV classification. [24,25] For comparison purposes, the classical coordination complex, the Creutz-Taube ion, [6,7,26] [3]…”

Transition from a Metal‐Localized Mixed‐Valence Compound to a Fully Delocalized and Bridge‐Biased Electrophore in a Ruthenium–Amine–Ruthenium Tricenter System

“…When the long-range-corrected functional UCAM-B3LYP was used, the spin density of 1 3 + -6 3 + is largely dominated by one ruthenium component with minor distributions from the central amine bridge, while the spin density of 7 3 + is dominated by the amine bridge (Supporting Information, Figure S22). Stimulated by the recent reports by Kaupp and Lambert, [29,30] we used the custom-defined UBLYP functional with 30 % HartreeFock (H-F) exchange to find that a transition from the ruthenium-localized to bridge-biased spin density distribution could be partially reproduced ( Figure 6). Using this method, the spin density of 1 3 + , 2 3 + , and 4 3 + was calculated to be dominated by one ruthenium component with minor contributions from the amine bridge, while that of 3 3 + , 5 3 + , 6 3 + , and 7 3 + was rather delocalized.…”