||Conjugated polymers have been explored for a broad spectrum of applications, particularly in optoelectronic and sensing material. These polymers contain a π-electron delocalized optically active backbone composed of phenylene segments, and 4,7-di(thiophen-2-yl)benzo-2,1,3-thiadiazole units (DTBT). In dilute solutions, the polymer emits in the blue region. Complex formation between the polymer and a hydrophobic BSA gives rise to polymer aggregation, leading to increased interchain contacts. Under these conditions, energy transfer between the phenylene units and the DTBT sites is more efﬁcient than that for isolated chains, and red emission dominates the solution ﬂuorescence. Addition of enzyme to the polymer-BSA aggregated solution results in a change in emission color from red to blue. Complex of the polymer and hydrophobic BSA was de-aggregated by adding trypsin, leading to decrease in interchain contacts and reduction of energy transfer from phenylene units to the DTBT units.