Synthesis, one and two-photon optical properties of two asymmetrical and symmetrical carbazole derivatives containing quinoline ring

The carbazole derivatives are suitable for two-photon absorption optical storage and photoluminescence material. Two carbazole derivatives, asymmetrical and symmetrical type molecules containing quinoline rings as electron acceptors and an N-ethylcarbazole group as electron donor, 9-ethyl-3-(2-quinolin)viny-carbazole (4) and 9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5), had been synthesized by the Vilsmeier reaction of formylation and Knoevenagel condensation. The one-photon properties including absorption, fluorescence emission spectra, fluorescence quantum yields and fluorescence decay behaviors were investigated in N,N-dimethylformamide. Meanwhile, these compounds were theoretically surveyed by the density functional theory (DFT) and the time-dependent functional theory (TD-DFT). The two-photon excited fluorescence and two-photon absorption cross-sections were measured for the compounds by 120 fs pulse at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate. The results showed that both of the two compounds 4 and 5 had higher fluorescence quantum yield (Φ) of 0.77 and 0.81 comparing with carbazole. Compounds 5 with symmetric π conjugated structure possessed longer fluorescence lifetime (τ) of 21.4 ns and larger two-photon absorption cross-sections (δTPA) of 364 × 10−50 cm4 s/photon than those of compounds 4 with asymmetric π conjugated structure (τ = 10.03 ns and δTPA = 81 × 10−50 cm4 s/photon). It was indicated that the one and two-photon optical properties of carbazole derivatives are influenced strongly by the symmetry and length of π conjugated structure.