A triplet-triplet (T-T) absorption spectrum of fluorobenzene was observed for the first time. The broad absorption in the region of 330-550 nm with lifetime of r = 0.7 mus was ascribed to the T-T absorption spectrum by the T-T energy transfer experiment using naphthalene as an acceptor. The spectrum reported preciously as the T T absorption was elucidated to be the spectrum of radical. Quantum yield of the intersystem crossing phi(IST) was determined to be 0.27 by use of the time-resolved thermal lensing (TRTL) experiment. (C) 2002 Published by Elsevier Science B.V.