Charles Chi Wang Law

Synthesis, thermal stability, and light-emitting properties of hyperbranched poly(phenylenegermolene)s

A germole-containing diacetylene, 1,1-diethynyl-2,3,4,5-tetraphenylgermole (2), was synthesized. Homopolymerization of 2 and its copolycyclotrimerization with 1-octyne were effected by TaCl5–Ph4Sn in toluene, producing completely soluble polymers (1) in moderate yields. The molecular structure of 1 was characterized by spectroscopic methods. The thermal stability of 1 was evaluated by thermogravimetric analysis, which detected virtually no weight loss when the polymers were heated to ∼350°C. These hyperbranched polymers were electronically conjugated as suggested by their strong absorption in the visible spectral region (λmax∼540 nm). Photoluminescence of the polymers was dramatically enhanced by cooling their solutions to low temperatures. Restricted intramolecular rotations of the phenyl rings upon the axes of the single bonds linked to the germole cores at the cryogenic temperatures might be responsible for this unique phenomenon of cooling-enhanced emission.