Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells, and light emitting diodes.We studied the how the optical absorption enhancement and bandage positions of PbS QDs are modified upon ligand exchange from oleate to a series of cinnamate ligands. We find that band edge positions of PbS QDs, can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust, and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. We find that within the cinnamate/PbS QD system the optical absorption is enhanced and the enhancement scales linearly with the HOMO/LUMO gap of the ligand and not their electron donating/withdrawing character, indicating that the ligand/QD coupling occurs equally efficient between QD VB/ligand HOMO levels and the QD CB/ligand LUMO levels. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the resulting emergent optical and electrical properties. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We demonstrate that the optical enhancement can be used to extract the ligand binding isotherms for a given QD/ligand complex by following the absorption enhancement during ligand exchange reactions. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.