A family of star-shaped conjugated oligofluorene molecules based around a central benzene core is studied with the aim of identifying how changes in molecular structure can affect the laser performance of organic materials. As the oligofluorene arm length increases the optical transitions are found to move to longer wavelength, there is an increase in photoluminescence quantum yield and a corresponding reduction in the excitation density for amplified spontaneous emission. Distributed-feedback lasers based on these materials are tunable across 402–462 nm with lasing thresholds as low as 1.1 kW cm−2 and efficiencies as high as 6.6%. The laser performance is compared with that of family of star-shaped molecules with different core structure. This shows that a reduction in intermolecular interactions is very important to achieving high performance lasing in organic semiconductors. ; Georgios Tsiminis, Neil A Montgomery, Alexander L Kanibolotsky, Arvydas Ruseckas, Igor F Perepichka, Peter J Skabara, Graham A Turnbull, and Ifor DW Samuel