Abstract: Provided in some aspects are methods for light-controlled in situ surface patterning of a substrate. Compositions such as nucleic acid arrays produced by the methods are also disclosed. In some embodiments, a method disclosed herein comprises using photocontrollable ligation of nucleic acid molecules with splints, wherein at least one of the splints comprises a photo-crosslinkable moiety. Photo-induced crosslinking of the splint to oligonucleotide molecules immobilized on a substrate allows the splint to remain attached to the oligonucleotide molecules during subsequent rounds of photoresist application and removal. A large diversity of barcodes can be created in molecules on the substrate via sequential rounds of light exposure, hybridization, and ligation.