Synthesis and Properties of Novel Well-Defined Alternating PPE/PPV Copolymers

Abstract

The polycondensation reactions of luminophoric dialdehydes 5 and bisphosphonates 3 provide a new type of π-conjugated polymers 7 with well-defined structure (—Ar—C≡C—Ar—C≡C—Ar—CH=CH—Ar— CH=CH—)n , which was confirmed by NMR, infrared and UV-Vis spectroscopy. High molecular weight (M̄w up to 500 000 g/mol), thermostable, soluble and transparent film-forming materials were obtained. The grafting of large alkoxy side chains enhances the solubility and processability of the new compounds. The incorporation of triple bonds into the PPV backbone increases the oxidation and reduction potentials, thus making these polymers potentially good electron-transporting materials if used in light-emissive-diode devices. The polymers are photoconductive and show very good photoluminescent properties in solution as well as in the solid state. Identical absorption (λmax,abs = 445 nm) and emission (λmax,em = 490 nm) behaviors were observed for all polymers in solution (CHCl3), resulting in a fluorescence quantum yield of 70%, but the photophysical behavior in solid state was side group dependent. Polymer 7ac shows a very large Stokes shift (137 nm) and lower fluorescence quantum yield (19%), whereas 7aa, 7bb and 7ab, consisting of side groups equal to or longer than O(CH2)11CH3 are characterized by smaller Stokes shifts (around 30 nm) and comparatively higher fluorescence quantum yields (34 to 44%).