A new photosensitive polymeric material for WORM optical data storage using multichannel two-photon fluorescence readout

We report image formation via photoinduced fluorescence changes in a polymeric medium with nondestructive two-photon fluorescence readout of a multilayer structure. A two-photon absorbing fluorescent dye possessing functional groups with differential basicity, (7-benzothiazolyl-9,9-didecyl-2,2-(N,N-diphenylamino)fluorene) (1), underwent protonation in the presence of a photoinduced acid generator upon exposure to a broadband UV light source or femtosecond 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. Experiments in polymer films demonstrate the changes in fluorescence properties of the fluorophores can be employed for a write-once read-many (WORM) data storage medium with a two-photon fluorescence readout. Two-channel, two-photon fluorescence imaging provided both "positive" and "negative" image readout capability.