Molecular Design of Silicon‐Containing Diazenes: Absorbance ofEandZIsomers in the Near‐Infrared Region

The effective use of photochromic systems based on azo compounds in a number of applications, especially biomedical and pharmacological ones, is impeded by the unresolved problem of theirE⇆Zisomerization in the near‐IR region, NIR (780–1400 nm). We have demonstrated at the TD‐DFT, STEOM‐DLPNO‐CCSD and CASSCF‐NEVPT2 levels of theory that the presence of a silylated diazene core −Si−N=N−Si− with three‐, tetra‐ or five‐coordinated silicon atoms practically guarantees the absorption of theEandZforms of such derivatives in NIR and the amazing (185–400 nm) separation of their first absorption bands. In particular, the maximumλ₁of the first n→π* band of theEisomer of azosilabenzeneASiBis at ∼1030 nm, while for theZisomerλ₁≅1340 nm. Based on the found bistable azo compounds (ASiB, bis(silyl)‐SiDand bis(silatranyl)‐SaDdiazenes) and their derivatives withEandZabsorption in NIR, unique photoswitches can be created for a number of applications, in particular, for photothermal therapy.