Fluorescent Polyimide Films with Covalently Incorporated Perylenediimide

Fluorescent polyimide films were manufactured using colorless, transparent polyimide (PI) as a matrix material and perylenediimide (PDI) as a covalently incorporated fluorophore. The matrix polymer was manufactured using fluorinated monomers of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2-bis(trifluoromethyl)benzidine. A slight excess of 6FDA was used to produce an acid anhydride-terminated polyamic acid (PAA) precursor. Amine-terminated PDI was prepared in advance through a high-temperature condensation reaction between perylene-3,4,9,10-tetracarboxylic acid dianhydride and two equivalent cycloaliphatic diamines. The acid anhydride-terminated precursor PAA was treated with the amine-terminated PDI to simultaneously extend the chain and confer fluorescence (FL), followed by chemical imidization to obtain fluorescent PIs. Well-featured PI films with a thickness of approximately 50 μm were fabricated via casting on glass slides and convection drying. The prepared PI films showed an elastic modulus of more than 4.4 GPa, a tensile strength of more than 81 MPa, a thermal decomposition temperature of more than 500 °C, at which a weight loss of 5% was observed, and a glass transition temperature of more than 306 °C. Moreover, the polymer films showed FL quantum efficiency of 5.74% or higher, with the FL color slightly differing depending on the cycloaliphatic diamine used in the synthesis of the PDI unit.