The nanosecond-scale propagations and optical-limiting properties of two fluorene derivatives-2, 7-bis(4′-(dimethylamino)-distyryl)-9H-fluorene (F1) and 2,7-bis(4′-(nitro)-distyryl)-9H-fluorene (F2) with different terminal groups are investigated by solving the coupled rate equations and field intensity equation using an iterative predictor-corrector finite-difference time-domain technique. The influence of the propagation distance (z), particle number density (N), and pulse width (τ) on the optical-limiting properties and two-photon absorption (TPA) of these molecules is analyzed. The calculations show that both F1 and F2 possess large two-photon absorption cross sections and pronounced optical-limiting properties. In addition, the nonlinear optical properties depend crucially on the terminal groups. F2, with terminal groups of ―NO_{2}, has much larger dipole moments, an enhanced two-photon absorption cross section, and superior optical-limiting ability compared with F1, which have terminal groups of ―N(CH_{3})_{2}.