Photophysical and Photochemical Properties of Anthryl-Labeled Polyimides:  Fluorescence, Electron Transfer, and Photoreaction

The photophysical and photochemical properties of two anthryl-labeled polyimides have been studied by absorption and fluorescence spectroscopy, single-photon counting, and picosecond transient absorption measurements. The observed emission decay is triexponential, with a very short-lived component of ∼50 ps being attributed to electron-transfer quenching by the polyimide backbone, a slower component of ∼2 ns assigned to excimer quenching, and a second long-lived component of ∼10 ns assigned to isolated anthryl chromophore emission. An anthryl cation radical is produced by flash excitation of the pendent anthryl chromophores. Irradiation of thin films of the anthryl-labeled polyimides at 350 nm in air results in the disappearance of the anthryl absorption bands and produces extensively photo-cross-linked polyimide thin films. Several possible photochemical reactions that might account for the disappearance of the anthryl absorption bands and subsequent photo-cross-linking are proposed.