In a method for creating polymer arrays through photoelectrochemically modulated acid/base/radical generation for combinatorial synthesis, electrochemical synthesis is guided by a spatially modulated light source striking a semiconductor in an electrolyte solution. A substrate having at its surface at least one photoelectrode that is proximate to at least one molecule bearing at least one chemical functional group is provided, along with a reagent-generating chemistry co-localized with the chemical functional group and capable of generating reagents when subjected to a potential above a threshold. An input potential is then applied to the photoelectrode that exceeds the threshold in the presence of light and that does not exceed the threshold in the absence of light, causing the transfer of electrons to or from the substrate, and creating a patterned substrate. The process is repeated until a polymer array of desired size is created.