Sonogashira coupling between 3,5,3',5'-tetrabromo-[2,2']bithiophene and various terminal alkynes provides two-photon absorption (TPA) chromophores 1-6, which possess electron donor (D) and/or acceptor (A) alkynyl substituents at 3(3') and 5(5') sites of the bithiophene core. The up-converted fluorescence emission excited at 800 nn (Ti:sapphire femtosecond laser, similar to 100 fs pulses) was used to determine the two-photon absorption cross-sections (Q) of these compounds. The corresponding TPA cross-section (a) values ranging from 132 to 1120 GM (10(-50) cm(4)s photon(-1)) can be fine-tuned by the substitutents. The quadrupolar-type (A-pi-D-pi-A) chromophore 5 exhibits the largest Q value (1120 GM) in CH2Cl2 upon 800 nm excitation. (c) 2006 Elsevier Ltd. All rights reserved
