Two dimethylamino-carbaldehyde derivatives with different π-bridge lengths were prepared,and their transient optical properties and photophysical mechanisms were investigated by transient absorption spectroscopy and Z-scan measurements.Owing to the difference in molecular structures,the two compounds exhibit different populations of locally excited states and,therefore,they also produce different transient absorption spectra.After photoexcitation,both molecular materials exhibit a wide excited state absorption band from 450 nm to 1000 nm.Meanwhile,the excited state lifetimes are dramatically different,2 ns and 100 ps,for the two molecules.A figure of merit greater than 2 at the wavelength of 1000 nm is obtained.The results show that modulating the population of the locally excited states in this type of molecule can be a promising approach for obtaining optical switching and solar cell materials.