Inter valence charge transfer

In spectrometry, the inter valence charge transfer (IVCT) band is a characteristic band for organic metal complexes that show valence tautomerization. Valence tautomers are a set of compounds that have almost the same chemical structure but different electronic structures. Complexes that have valence tautomers usually consist of two redox active sites, between which electron transfer reversibly occurs. Therefore, a valence tautomer is converted to another tautomer by the electron transfer from one redox site to another, and the origin of the IVCT band can be understood as the electron transfer between valence tautomers.

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The IVCT band is usually observed in the visible to near infrared region as a very broad absorption band. Since the energy states of valence tautomers affect the IVCT band, the strength of electronic interaction between redox active sites (α: mixing coefficient) can be determined by analysis of the IVCT band. Depending on the value of α, valence tautomeric complexes are classified into three groups. First, when α is about 0, the complex has no interaction between redox sites, so no IVCT band is observed. These complexes are called class I complexes. Second, when α is 0 to 0.707, there is some interaction between sites and the IVCT band is observed. These are class II complexes. And third, when α is over 0.707, interaction between redox sites is very strong and it is better to consider these sites as one united site, not as two isolated sites. These complexes are categorized as class III complexes.