Synthesis and characterization of highly fluorescent main-chain copolyimides containing perylene and quinoxaline units

Two series of copolyimides, poly(quinoxaline perylene bisimide)s and poly(quinoxaline perylene bisimide ether)s, carrying quinoxaline units and varying amounts of substituted perylene bisimides in the main chain have been synthesized. The polymers were characterized by FT-IR, NMR, UV/vis, and fluorescence spectroscopy as well as GPC, DSC, and TGA measurements. They are highly soluble in usual solvents like CHCl3, THF, etc., and form optically transparent films. The incorporation of varying amounts of perylene diimides with different substitution patterns allowed the control of fluorescence wavelength and intensity in solution and in thin films. The copolyimides with I mol % of perylene diimide content exhibit highest solid-state fluorescence. The observed intense fluorescence and a constant maximum wavelength of absorption in the solid state for copolymers containing up to 2.82 mol % perylene content indicate the absence of chromophore aggregation. Both types of copolymers are thermally stable up to 420 degreesC and exhibit glass transition temperatures in the range 225-270 degreesC. Blends of these perylene-containing polymers with hole transport molecules show complete photoluminescence quenching due to efficient electron transfer.