The combination of efficient light emission and high charge-carrier mobility has thus far proved elusive for polymer semiconductors, with high mobility typically achieved by cofacial -electron system to -electron system interactions that quench exciton luminescence. We report a new strategy, comprising the introduction of a limited number of more effective hopping sites between otherwise relatively isolated, and thus highly luminescent, polyfluorene chains. Our approach results in polymer films with large mobility (3-6×102 cm2 V1 s1) and simultaneously excellent light-emission characteristics. These materials are expected to be of interest for light-emitting transistors, light-emitting diode sources for optical communications and may offer renewed hope for electrically pumped laser action. In the last context, optically pumped distributed feedback lasers comprising one-dimensional etched silica grating structures coated with polymer have state-of-the-art excitation thresholds (as low as 30 W cm 2 (0.1 nJ per pulse or 0.3 J cm2) for 10 Hz, 12 ns, 390 nm excitation) and slope efficiencies (up to 11%). © 2008 Nature Publishing Group.