A microfluidic system comprising a plurality of photochemical reaction stages, the microfluidic system comprising a computational processor, a plurality of electrically-controllable photochemical reaction stages, and a series of controllable interconnections for connecting the photochemical reaction stages. In an implementation, the computational processor controls the electrically-controllable photochemical and other chemical reaction stages together with controllable interconnections so as to implement multi-step chemical processes. The microfluidic system can be configured to selectively drive a plurality of photochemical reactions within a mixture of chemical compounds via controlled emission of light of a plurality of wavelengths. The microfluidic system can be configured to comprise various interconnections and combinations of parallel and series chemical reaction stages, and can include a multichannel microfluidic chemical transfer bus. The microfluidic system can be configured to handle and process liquid, gasses, solids, and mixtures of these, and can used to implement anion relay chemistry, combinational chemistry, and synthon-based synthesis.