You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 2-N'-dibenzothiophen-2-yl-2-N',4-N-diphenyl-4-N-(4-phenylphenyl)-9,9'-spirobi[fluorene]-2',4-diamine .
user
C61H40N2S
assistant