Building oil a previous design for a Ru-based dissolved N-2 sensor, we report an adaptation that allows for reversible data storage. The N-2 complex can be "fixed" and made stable across file Substitution of OH-with F- to form a range of pHs by [Ru-II(F)(TMC)(N-2)](+) (1, TMC = 1,4,8,11-tetramethyl-1,4,8,11 tetraazacyclotetradecane). The addition of Ca2+ and irradiation with light at high pH removes the F-, thereby regenerating the sensor in its reversible configuration.