AbstractA rational approach towards precision two‐dimensional (2D) assemblies by crystallization‐driven self‐assembly (CDSA) of poly(L‐lactides) (PLLAs), end‐capped with dipolar dyes like merocyanine (MC) or naphthalene monoimide (NMI) and hydrophobic pyrene (PY) or benzene (Bn) is described. PLLA chains crystallize into diamond‐shaped platelets in isopropanol, which forces the terminal dyes to assemble into a 2D array on the platelet surface by either dipolar interactions or π‐stacking and exhibit tunable emission. Dipolar dyes play a critical role in imparting colloidal stability and structural uniformity to the 2D crystals, which is partly compromised for hydrophobic ones. Co‐crystallization between NMI‐ and PY‐labeled PLLAs yields similar diamond‐shaped co‐platelets with highly efficient (≈80 %) Förster Resonance Energy Transfer on the 2D surface. Further, the “living” CDSA method confers enlarged, segmented block co‐platelets using one of the homopolymers as “seed” and the other as “unimer”.