Image formation via photoinduced fluorescence changes in a polymeric medium with two-photon fluorescence readout of a multi-layer structure. Fluorophore-containing polymers, possessing one or more basic functional groups, underwent protonation in the presence of a photoinduced acid generator upon exposure to a broad-band UV light source or fast-pulsed red to near-IR laser irradiation. Solution studies demonstrated formation of monoprotonated and diprotonated species upon irradiation, each resulting in distinctly different absorption and fluorescence properties. The fluorescence of the original, neutral, fluorophore was reduced upon monoprotonation leading to a concomitant increase in fluorescence at longer wavelengths due to the monoprotonated form, the basis for multichannel data readout. Experiments in polymer films demonstrate the changes in fluorescence properties of the photosensitive polymer compositions and polymers can be employed for a high storage density, write-once read-many (WORM) data storage medium with two-photon fluorescence readout. Two-channel, two-photon fluorescence imaging provided both "positive" and "negative" image readout capability.