Catalyzes the dehydrogenation of both 9-fluorenol and 1,1a-dihydroxy-1-hydro-9-fluorenone to produce 9-fluorenone and 2'-carboxy-2,3- dihydroxybiphenyl, respectively. 9H-fluoren-9-ol + NADP(+) = 9H-fluoren-9-one + H(+) + NADPH 9H-fluoren-9-ol + NAD(+) = 9H-fluoren-9-one + H(+) + NADH Aromatic compound metabolism. Belongs to the short-chain dehydrogenases/reductases (SDR) family.