Photoswitchable mixed valence

Abstract

For a molecular electronics technology to be fully serviceable, switching functions will be indispensable. 5 Specifically, it will be desirable to control the conductivity of a given molecule using an external stimulus. Photoswitchable mixed valence systems are comprised of a reversibly photoisomerizable bridging unit connecting two redox-active moieties, and as such represent some of the most simple chemical systems in which switching of charge delocalization can be explored. As photoisomerizable units, dithienylethenes have received much attention in the context of photoswitchable mixed valence, but 10 there are also more exotic examples such as norbornadiene-and dimethyldihydropyrene-based switchable systems. As redox-active units responsible for the mixed valence phenomenon, both metal-containing as well as purely organic moieties have been employed. Typical investigations in this area involve the comparison of cyclic voltammograms and (near-infrared) optical absorption spectra of the two isomeric forms of a given system. The magnitude of the comproportionation constant and evaluation of 15 intervalence absorption bands using appropriate theoretical models yield information regarding the extent of charge delocalization in the two isomeric forms. In several of the compounds investigated so far, the light stimulus induces a substantial increase of charge delocalization, or in the terminology commonly used in mixed valence chemistry, a changeover from class I to class II or even class III behavior.

Macrocyclic N-Methylated Cyclic Peptides and Depsipeptides

“…Later, it was discovered that the hydroxyl group and double bond in the MeBmt residue were important as structural variations of these groups caused a loss of immunosuppressive activity [45]. The absence of a methyl at C-4 or the presence of an extra methyl group at this position caused the activity to be diminished.…”

Charge Delocalization in a Homologous Series of α,α′-Bis(dianisylamino)-Substituted Thiophene Monocations

“…36 Another exception is our own recent investigation of photoswitchable organic mixed-valence in dithienylethene systems. [37][38] Scheme 1. Chemical structures of the molecules investigated in this work.…”

Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study

“…Reliably predicting their properties and determining the origin of mixed-valence effects remains open and dependent upon correlating the properties with the molecular and crystal structure, and with local chemistry. Apart from the field of metallurgy and pigments in artwork and ceramics (e.g., Fe 2 O 3 and Fe 3 O 4 ) [1], it also serves as an active area of research in complex biophysical problems, such as photosynthesis, and in organic-conjugated materials [2] for artificial electronic devices [3]. What makes these compounds different from other materials is the coexistence of wide s-d bands and very heavy atomiclike f electrons at/near the Fermi energy.…”