The fabrication of nanostructures from polycyclic aromatic hydrocarbons (PAHs) is highly attractive owing to their unique optical, electrical, and magnetic properties. However, the creation of uniform and well-defined PAH nanostructures by self-assembly still remains a significant challenge. Herein, we report that highly uniform hexagonal rods can be obtained from triphenylene (TP)-derived monomers by synchronized polymerization and self-assembly (SPSA). These rods have a single-domain columnar liquid crystalline structure in which columns formed from stacked TPs are along the long axis of the rods. The length/diameter ratios of the rods can be tuned over a wide range. Key factors to achieve SPSA of PAHs were analyzed, and the formation mechanism was clarified. In particular, it is observed that successful SPSA occurs below an upper critical temperature, which could be attributed to insufficient microphase separation between the side chains and the main chains and should be a general principle for SPSA. Furthermore, we demonstrate that the columnar stacking of TP units significantly promotes the intersystem crossing of the singlet excited state to the triplet excited state, resulting in simultaneous fluorescence and phosphorescence emission at room temperature. This work may be extended to a wide range of PAHs to regulate their self-assembly and light emission properties.