Pyridazine-Containing Diazatwistanthracene and Tetraazatwisttetracene: Synthesis, Crystal Structures and Third Order Non-linear Optical Properties

In this paper, two pyridazine-heterocycles-containing azaacenes 9,12-diphenylphenanthro[4,5-fgh]phthalazine (DPPA) and 2,9-di-tert-butyl-4,7,11,14-tetraphenylpyridazino[4',5':9,10] phenanthro[4,5-fgh]phthalazine (TPPA) have been synthesized and fully characterized. The single crystal analysis of TPPA showed that TPPA molecule exhibits a twisted structure with the dihedral angel of 27 degrees between pyrene and pyridazine unit, which suppresses the pi-pi stackings in the solid state. The two-photon absorption properties of DPPA and TPPA were investigated, respectively, by using the femtosecond Z-scan technique. The results showed that both DPPA and TPPA showed moderate two-photon absorption cross-section values, and the larger one was found to be 454 GM with TPPA. Obviously, the introduction of pyridazine ring into the skeleton of acenes forming a A-D-A structure could lead to a much larger two-photon absorption coefficient and two-photon absorption cross section.