A novel fluorescent poly(pyridine-imide) acid chemosensor

A novel diamine containing heterocyclic pyridine and triphenylamine substituents namely, 4-(4-triphenylamine)-2,6-bis(4-aminophenyl)pyridine was synthesized via the Chichibabin reaction and reduction. The diamine was used in the preparation of poly(pyridine-imide) by direct polycondensation with 4,4′-hexafluoroisopropylidenediphthalic anhydride in N-methyl-2-pyrrolidinone. The poly(pyridine-imide) was converted into a lightly colored, optically transparent, flexible and tough polyimide film which exhibited good thermal stability (Td10 = 538 °C) in air and high glass transition temperature (Tg = 342 °C); the polyimide film had a tensile strength of 71 MPa and a tensile modulus of 2.2 Gpa. The UV–vis absorption cutoff at 400 nm and fluorescence at ∼600 nm following protonation with acid, enable the film to act as an “off–on” fluorescent switcher for acids.