3D optical data storage based on two-photon processes provides a mechanism for writing and reading data with less crosstalk between multiple memory layers, due to the quadratic dependence of two-photon absorption (2PA) on the incident-light intensity.[1] This capacity for highly confined excitation and intrinsic 3D resolution affords immense information storage capacity (up to 10 12 bits cm -3). [2] Recently, the use of photochromic materials for 3D memory has received intensive interest because of several major advantages over current optical systems, including their erasable/rewritable capability, high resolution, and high sensitivity. [3] Among the several classes of photochromic materials, diarylethenes with heterocyclic aryl groups are the most promising candidates for applications because of their excellent fatigue resistance, picoseconds switching time, high photoisomerization quantum yields, and absence of thermal isomerization. [4,5] Various optical systems for reading and writing 3D memories using diarylethene derivatives as storage media have been reported, [3] where several methods using fluorescence readout were used to avoid destructive readout. [4] In particular, Jares-Erijman and Irie used Lucifer Yellow I as the donor and bis(thienyl)ethane as the acceptor to build fluorescent molecules and they developed a general conceptual reading/writing system based on fluorescence resonance energy transfer (FRET), where they found that the single-photon fluorescence emission of the donor is reversibly modulated by cyclical transformations of the photochromic acceptor upon irradiation with appropriate UV and visible light. [5,6] This system provided a novel method of using fluorescence to readout the recorded data without simultaneously erasing part of the stored information. However, to the best of our knowledge, modulation of the twophoton fluorescence emission of a dye by a photochromic diarylethene has not been reported as the readout method in a 3D optical-data-storage system. This may be due, in part, to the difficulty in making suitable materials with large 2PA cross sections, high fluorescence quantum yields, and high photostability, in which the emission spectrum properly overlaps the absorption spectrum of one of the isomers of the photochromic diarylethene. In this paper, we demonstrate a novel two-photon 3D optical-storage system based on the modulation of the fluorescence emission of a highly efficient two-photon absorbing fluorescent dye and a photochromic diarylethene. This system is suitable for recording data in thick storage media and providing a non-destructive readout method without exhibiting any apparent fatigue, even after 10 000 readout cycles. The storage medium consists of a commercial available photochromic molecule (diarylethene 1), 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene, and a specially designed two-photon absorbing dye (2,7-bis[4-(9,9-didecylfluoren-2-yl)vinyl]phenylbenzothiazole (fluorene derivative 2) (Scheme 1). Figure 1 shows the absorption spectra of t...

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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-didecyl-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). Föster 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.