Photochromic polymer composites for two-photon 3D optical data storage

In this paper we demonstrate 3D two-photon recording and two-photon readout in photochromic polymer composites containing a mixture of 1,2-bis(2- methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene (diarylethene 1) and fluorene derivatives 2,2′-(9,9-didecyl-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl) bis(4,1-phenylene)) dibenzo[d]thiazole (2) or poly(9,9-didecy1-2,7- dipheylaminofluorene) (3). The recording mechanism in this system is based on two-photon excitation of the closed form of diarylethene 1 at 800 nm. The readout mechanism is based on the modulation of the emission intensity of fluorene derivatives 2 or 3 by the closed form of diarylethene 1 through Resonance Energy Transfer (RET). Foster distances (R ₀) and critical concentrations (A ₀) were calculated from the spectral overlap of the donor's emission (fluorene derivatives) and the acceptor's absorption (closed form of diarylethene 1) in solution and in polymer films of PMMA-co-VBP. This system was demonstrated to be suitable for recording data by two-photon excitation in thick storage media. The RET-based readout method proved to be essentially nondestructive (exhibiting a loss of the initial fluorescence emission less than 20% of the initial emission after 10 000 readout cycles), providing a solution to a long-standing challenge in photochromic optical data storage.