Two new stable organoboron compounds with dimesitylboryl group as electron acceptor and styrylthiophene as conjugated bridge have been synthesized, which are named trans,trans-2-dimesityl- boryl-5-(2-(4-(2-(thien-2-yl)vinyl)phenyl)vinyl)thiophene (1) and trans,trans-1,4-bis[2-(5-dimesitylborylthien-2-yl)vinyl]benzene (2). The former is asymmetrical dipolar molecule and the latter is symmetrical A-π-A type quadrupolar molecule. The compounds with different symmetry exhibit different two-photon absorption properties. To dipolar molecule 1, the energy levels of the excited states by single- and two-photon absorption processes are very close, but to quadrupolar molecule 2, the level of the excited state by two-photon absorption is about 0.35 eV higher than that by single-photon absorption. Pumped by laser pulses from 710 to 900 nm in femtosecond regime, both compounds 1 and 2 showed strong green up-converted fluorescence in THF solution with λ_max＝505 nm for 1 and λ_max＝513 nm for 2. Under the excitation of 775 nm light, the two-photon absorption cross-section of 2 was measured to be 1340 GM by two-photon fluorescence method.

Key words: organoboron compound, two-photon absorption, up-converted fluorescence