You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2',7'-dimethyl-2,3-bis(octa-1,3,5,7-tetraynoxy)-6,7-bis(octa-2,4,6-triynoxy)-9,9'-spirobi[fluorene] is the IUPAC name of a molecule. Please give its molecular formula.
user
C59H28O4
assistant