This article reports the systematic functionalization of FIrpic (1) with solubilizing alkyl groups (complexes 2–4) or mesityl groups (complexes 5 and 6). Complex 5 is shown to offer significant advantages over FIrpic (1) in terms of performance of sky-blue polymer-based phosphorescent organic light-emitting diodes (PhOLEDs) with a solution-processed emitting layer (λmaxEL 477 nm for 5). Devices with 5 doped into poly(vinylcarbazole) (PVK):OXD-7 gave a maximum luminous efficiency of 19.1 cd A–1 at a brightness of 5455 cd m2 with EQE 8.7%. Optimized multilayer devices with additional TPBi and LiF layers gave 23.7 cd A–1 and EQE 10.4%. These data compare favorably with leading literature values for sky-blue polymer-based PhOLEDs. The enhanced performance of 5 is ascribed to three main reasons: (i) reduced concentration quenching of 5; (ii) the higher radiative yield of 5; and (iii) improved solubility of 5 in organic solvents. Complex 5 should find widespread use as a soluble blue phosphor for displays and lighting applications using solution processing techniques.