Ab‐initio multireference study of an organic mixed‐valence Spiro molecular system

Abstract

The electronic structure and some electron transfer properties of a model mixed-valence Spiro molecular cation have been investigated at CAS-SCF, CAS+S, and CAS+SD levels starting from canonical and localized orbitals, using SZ, DZ, and TZP basis sets. The potential energy surfaces of the adiabatic ground and the lowest three excited electronic states have been computed, within a two-state model, and a double-well potential has been obtained for the ground electronic state. We have demonstrated the low coupling interaction between the two redox moieties of this molecular cation by following the charge localization/delocalization in the valence pi system through the reaction coordinate of the intramolecular charge transfer. The effect of dynamical correlation, using either localized or canonical orbitals, was found to be crucial for a quantitative description of the electronic structure and some important electron transfer parameters of this mixed-valence system.

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

“…Results of the few CASSCF calculations available so far on (relatively small) organic MV systems suggest that these do not sufficiently correct for the tendency of UHF calculations to over-localize. 43,58,59 A large configuration-interaction or coupled-cluster calculation that takes into account higher-order excitations, or a suitable multi-reference-CI or -perturbation calculation, accounts for both dynamical and non-dynamical correlation effects. Such methods should thus be adequate.…”

Organische gemischtvalente Verbindungen: ein Spielplatz für Elektronen und Löcher

“…Ab-initioRechnungen an organischen MV-Verbindungen jenseits des SCF-Limits sind selten und auf sehr kleine Systeme beschränkt. [143][144][145] Andererseits tendieren Dichtefunktionalmethoden dazu, wegen des Selbstwechselwirkungsfehlers sogar in lokalisierten Klasse-II-Systemen Ladungen zu delokalisieren. [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.…”

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

“…[112] Ab initio UHF calculations suffer from the same problem as the AM1-UHF calculations, but ab initio calculations on organic MV compounds beyond the SCF limit are scarce and restricted to very small systems. [143][144][145] On the other hand, density functional methods tend to delocalize charge even in localized class II systems because of self-interaction error. [117,133,146] Recently, Kaupp and co-workers were able to overcome this problem by adjusting the exact HF exchange admixture in hybrid density functional methods to reproduce correctly the classII/ classIII borderline behavior in bis(triarylamine) radical cations.…”