.DELTA.9,9'-Bifluorene 1,2-Bis(biphenylene)ethylene 746-47-4 9,9'-Bifluorenylidene 9,9'-Difluorenylidene 9H-Fluorene, 9-(9H-fluoren-9-ylidene)- Bifluorenylidene Bisfluorenylidene Dibiphenyleneethene Dibiphenyleneethylene Difluorenylidene Diphenyleneethylene NSC12425 Tetrabenzfulvalene