You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance N-(9,9-dimethylfluoren-2-yl)-2,7,7'-triphenyl-N-(2-phenylphenyl)-9,9'-spirobi[fluorene]-2'-amine .
user
C70H49N
assistant