What is this SMILES notation: C[Si](C)C |^1:1|
The SMILES syntax in question is neither mentioned in the Daylight Theory Manual, nor in the OpenSMILES specification.

It is not part of the canonical SMILES syntax, but an extension, developed  by the ChemAxon company.

According to their documentation, extensions are tagged by leading and trailing | (pipe) symbols. ^1:, followed by an atom index, indicates a     


  monovalent radical center: