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

A series of high molecular weight copolyimides containing various amount of perylene units in the main chain have been synthesized. The polymers were characterized by FT-IR, NMR, UV/Vis, fluorescence spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis measurements. They are highly soluble in conventional solvents such as CHCl₃, THF, cyclohexanone etc. and form optically transparent films by solution casting or spin coating. The incorporation of various amount of perylene units in the main chain allows the control of the fluorescence intensity in solution and in solid thin films. The copolyimide containing 0.28 mol% perylene units exhibits the highest solid-state fluorescence. The observed fluorescence intensities of the copolyimides in solid state film decreased with the increasing amount of perylene units in the main chain when the mole ratio of perylene units greater than 0.28 mol% indicating the aggregation of chromophores. The copolyimides are thermally stable up to 400 °C and exhibit glass transition temperatures in the range of 340-360 °C. The number average molecule weight ranges from 1.72×10⁴ to 1.25×10⁵ and the molecule weight distribution mediated between 1.9 and 2.4.