Symmetrical fluorescent oligothiophene and benzene centered bispyrenoimidazole derivatives with double n-dodecyl chains showing high thermal stability

A family of symmetrical oligothiophene (dithiophene, terthiophene, and quaterthiophene) or benzene centered bispyrenoimidazole derivatives, having the same coplanar pyrenoimidazole terminal groups at each side, has been synthesized via Radziszewski, N-alkylation, and the following Pd(PPh3)4 catalyzed Suzuki and Stille coupling reactions. Double n-dodecyl chains are introduced to the molecules at the same time in order to increase their solubility in organic solvents. UV-vis and fluorescence spectra as well as thermal properties have been studied. The results demonstrate that compound 4 with a benzene linker displays the strongest fluorescence intensity, and oligothiophene centered bispyrenoimidazole derivatives 5-7 show obvious bathochromic shifts compared with benzene centered compound 4. It is worth mentioning that this family of compounds exhibits excellent thermal stability with the decomposition temperature higher than 400 °C even if the incorporation of double n-dodecyl chains. Furthermore, X-ray single-crystal structures of one representative compound 4·(CHCl3)2 and an intermediate 3 have been described.