Alkyne polycyclotrimerizations are effected by tantalum- and cobalt-based catalysts, giving soluble hyperbranched polyarylenes (HPAs) with high molecular weights (M_w up to ~2 × 10⁵) in high yields (up to 99.9%). All the HPAs exhibit excellent thermal stability, losing little of their weights when heated to > 400 °C. The HPAs graphitize when pyrolyzed at 800 °C in high yields (up to 86%). Upon photoexcitation, the HPAs efficiently emit strong deep-blue and blue-green light with fluorescence quantum yields up to 98%. The HPAs strongly attenuate intense laser pulses, with their limiting performances being superior to that of C₆₀, a well-known optical limiter. To cite this article: M. Häußler, C. R. Chimie 6 (2003).