Photochromic ring opening reaction dynamics of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene in solution has been studied by femtosecond time-resolved fluorescence and transient absorption measurements. Time profiles of the transient absorption at several different probe wavelengths are identical, showing two time constants, 4 and 22 ps. The spontaneous fluorescence reveals time profiles identical to that in the transient absorption. A simple one step ring opening reaction mechanism is proposed, where the closed form in the excited state reaches the open form in the ground state through nonadiabatic curve crossing. The ring opening reaction rate is determined to be in the range (1.7-4) x 10(10) s(-1). A single 66 cm(-1) wave packet motion in the excited state is observed, whose role on the ring opening reaction is speculated upon.