A three-armed star-shaped single-polymer system comprising tris(4-(3-hexyl-5-(7-(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)phenyl)amine (TN) as red emissive cores, benzothiadiazole (BT) as green emissive dopants, and polyfluorene (PF) as blue arms was successfully developed, in which the construction of the star shaped architectures can depress intermolecular interactions and concentration quenching. The thermal, photophysical, electrochemical, electroluminescent, and amplified spontaneous emission (ASE) properties of the synthesized polymers are systematically investigated. The modulation of the doping concentration of TN and BT can guarantee the partial energy transfer in a star-shaped single-polymer system, further achieving saturated white emission. Consequently, a current efficiency of 2.41 cd A(-1) and Commission Internationale d'Eclairage (CIE) coordinates of (0.34, 0.35) were R3G4 with 0.03 mol % red core and 0.04 mol % green dopants. The saturated white emission is likely to result from the fine control of partial energy transfer and suppressed intermolecular interactions due to the construction of such a star-shaped single polymer system. What is more, TN-R3G4 shows impressive ASE characteristics with relatively low threshold of 63 +/- 5 mu J/cm(2), which demonstrates the potential as gain media for organic lasing applications. Our results have provided new insights and better understanding into the photophysical and optoelectronic behaviors of the resulting star-shaped single-polymer systems with simultaneous RGB emission.