The solid-state microstructure of semiconducting polymers is known to influence properties relevant for their function in optoelectronic devices. While several strategies exist in the literature for controlling desired morphological organization, preaggregation in solution via polymer chain end-functionalization remains relatively unexplored. In this work, we synthesized two poly(3-hexylthiophene) (P3HT) derivatives with different end-groups by using click chemistry. End-groups chosen for this study were derivatives of sulforhodamine 101 dye and phenyl-C-61-butyric acid methyl ester (PC60BM). The chemical functionality of the end-group is found to influence the aggregation properties as a function of solvent quality. End-group-induced preaggregation ultimately impacts the optical properties and molecular orientation in the solid state. These results suggest future applications of this structural modification strategy to modulate device characteristics.