In this study, three π-conjugated copolymers (PPTBT, PPT, and PPP) functionalized with the same length of the Guerbet-type side chains but different insertions of π-conjugated units were designed and synthesized. These copolymers exhibited intense blue, green, and red emissions in a solvent-free state with good fluidity at room temperature. The effects of different π-units on the photophysical and rheological behaviors, miscibility, and microphase separation of these polymer liquids were thoroughly explored. Compared with conventional conjugated polymers, photophysical, thermal, and morphological results and rheological analysis showed that three copolymer liquids exhibited intensive emissions and high viscoelasticity in the condensed state, enabling the direct visualization of microphase separation behaviors by polymer blending techniques. These findings suggested that the use of highly viscoelastic conjugated polymer liquids with excellent fluorescence can play a critical role in the future design of efficient luminescent polymer liquids for the next-generation optoelectronically and external stimuli-responsive smart soft materials.