Two‐Photon 3D Optical Data Storage via Aggregate Switching of Excimer‐Forming Dyes

Abstract

Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [3][4][5][6] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ] The optical changes considered for rewritable and write-once read-many three-dimensional (3D) ODS storage media based on TPA include reversible and irreversible photo chemical reactions such as photoisomerizations, [8][9][10] photo-induced dimerizations, [ 11 , 12 ] photodecompositions, [ 13 , 14 ] and photopolymerizations. [15][16][17] Fluorescent photochromic systems have attracted particular interest, because the exploitable photophysical processes are fast, effi cient, and reversible. [18][19][20] However, it has been challenging to create fl uorescent photochromic materials, which combine high stability, high fl uorescence quantum yield, and large TPA cross-section. We here demonstrate a novel approach to 3D ODS materials, which relies on the switching of the aggregation state of an excimer-forming fl uorescent dye with an appreciable TPA cross-section in an inert host polymer.We have previously reported a range of materials, which change their fl uorescence and/or absorption properties upon exposure to heat, [21][22][23] chemicals, [ 24 ] or mechanical forces, [25][26][27] on account of reversible or irreversible stimulusinduced changes of the aggregation state of the dye molecules. We surmised that such changes could be induced in small volumes by TPA-induced local heating and therefore explored a melt-processed blend of poly(ethylene terephthalate glycol) (PETG) and 1.1% w/w of 1,4-bis( α -cyano-4-octadecyloxystyryl)-2,5-dimethoxybenzene [ 22 , 23 ] (C18-RG, Figure 1 a) as TPAaddressable ODS medium. C18-RG was selected on account of its signifi cant changes in absorption and emission spectra upon aggregation/dissociation, its high thermal and photochemical stability, and, as demonstrated here, its appreciable TPA cross-section. PETG was chosen as the matrix due to its glassy nature and transparency in the relevant op...

Two-Photon Responsive Metal–Organic Framework

“…This kind of 3D two-photon excited fluorescence patterns may find usage in 3D optical storage. 34,46 In summary, we developed a two-photon responsive MOF crystal ZJU-56-0.20 which shows significant red-shift change in two-photon excited fluorescence, ascribed to the photochemical reaction of the zwitterionic organic linkers, under the femtosecond laser. The nonlinear optical nature allows for two-photon patterning and imaging in high-resolution (1×1×5 μm 3 ) 3D structure.…”

“…29,30 The task of manipulating the properties of MOFs in 3D can be realized by the usage of nonlinear optical effects, in particular through the multi-photon absorption. This is because such nonlinear optical processing has the advantages such as tight focus and deep penetration over linear absorption effects, [31][32][33][34] and therefore can initiate reactions in the defined focal regions of laser within the bulky materials. [35][36][37] However, very rare multiple-photon responsive MOFs have been developed so far.…”

Low-power photon upconversion through triplet–triplet annihilation in polymers

“…Our group has used melt-processing to create homogeneous high-dye-content blends of PMMA and up to 0.16 and 25 wt% of PdOEP and DPA, respectively. [69][70][71][72][73] These materials were made by melt-mixing the components at 210 C (where the mixture is thermodynamically miscible), and quenching the materials to below T g , thereby kinetically trapping homogeneously blended materials. Unlike solution-cast reference blends of a similar dye content, which had a phase-separated morphology and showed no appreciable upconversion, TTA-UC occurred readily in these molecularly mixed blends.…”

“…6,109,110 For instance, two-photon absorption has proven useful in the context of solid-state optical data storage. 71 By focusing an intense laser beam (3 mJ over 10 ns) onto twophoton absorbing dyes, aggregation and de-aggregation of the excimer-forming cyano-oligophenylene vinylenes in poly-(ethylene terephthalate glycol) allowed us to alternate between ''on'' and ''off'' states. The development of TTA-UC photochemical reaction could bring about the possibility to operate at lower powers and therefore make more efficient storage devices.…”

One/two-photon cationic polymerization in visible and near infrared ranges using two-branched sulfonium salts as efficient photoacid generators

“…2 PA-related processes, such as nonlinear transmission and quadratically intensity-dependent properties, are utilized in optoelectronic devices, including 3D optical data storage systems [2]. The process can also be adopted in triggering subsequent events, such as fluorescence or chemical reactions [3,4] in biological imaging, photodynamic therapy [5], and 3D photolithography [6e9].…”