A simple synthesis route with a high yield of novel asymmetric cyclopentanone dyes 3a-3e and their highly two-photon up-converted fluorescences are reported. The dyes have good solubilities in most of ordinary solvents, a wide UV absorption wavelength range from 380-540 nm, and high fluorescence quantum yields. The two-photon absorption cross-sections of dyes 3a-3e were measured in chloroform by a two-photon induced fluorescence method. All of these properties of the new dyes make them suitable for being used as two-photon fluorescent probes.
