A Novel Strategy for Two‐Photon Holographic Recording: Stepwise Two‐Photon Absorption of α‐Quinquethiophene Followed by Energy Transfer to an Aryl Azide

Abstract

Owing to the drastic advances in information technology, the development of fast, high-density 3D optical data storage is a key issue.[1] Consequently, much attention has been paid to multilayered recording to realize 3D data storage.[2] Meanwhile, holographic recording, by which information is stored as an optical interference pattern produced by two intersecting coherent object and reference beams, serves as a valuable method for optical data storage.[3] Therefore, holographic recording into a multilayered medium constitutes a highly promising approach for the realization of 3D optical memory with excellent performance. However, conventional holographic recording systems cannot be applied to this approach because the information recorded into a layer is erased when a read/write process is effected on other layers. To overcome the problem of such destructive processes, two-photon holographic recording appears to be an attractive method. This technique involves excitation of a p-conjugated organic molecule from a ground state (S 0 ) to a higher triplet state (T n ) via S 0 -S 1 absorption by a gate laser, subsequent intersystem crossing (S 1 to T 1 ), and finally T 1 -T n absorption by a holographic light consisting of object and reference beams (Scheme 1a).[4] The higher triplet state induces a photochemical reaction in the recording medium, resulting in a change of refractive index; that is, resulting in a data-writing process. In this system, only a layer irradiated by the gate light is photoreactive towards the holographic light, and any layers not subjected to gate irradiation remain intact during the storage and retrieval of data by the holographic light. Although a-diketones such as biacetyl and benzil dissolved in an a-cyanoacrylate polymer have been demonstrated to achieve such twophoton holographic recording, the diffraction efficiencies were not sufficient for realizing multilayered recording, probably because of the low molecular extinction coefficients for the S 0 -S 1 and T 1 -T n transitions. [5] Hence, the use of p-conjugated molecules that exhibit large molecular extinction coefficients at the transitions is ideal for high-performance, twophoton holographic recording. Oligothiophenes are attractive materials to fulfill such criteria, [6] but the T n states themselves cannot induce any chemical reactions at the recording medium. Therefore, we considered the simultaneous use of an acceptor that can receive energy from the T n state of the oligothiophenes and induce chemical reactions to result in data writing (Scheme 1b). Reported herein is a novel strategy for efficient two-photon holographic recording that involves twophoton absorption of an a-quinquethiophene and subsequent energy transfer to an aryl azide.In the beginning, we focused our attention on a-quinquethiophene (1a: R = H) as a two-photon absorber because its UV and T-T absorption maxima (417 nm and 630 nm, re-COMMUNICATION 1826

Silicon-Based Cross-Coupling Reactions Through Intramolecular Activation

“…Some of these silylated quinquerthiophenes serve as novel two photon absorbing materials. 24 By taking advantage of various O protecting groups that can be orthogonally attached and removed, oligoarenes having three silyl moieties with different O protections are also accessible by iterative cross coupling/deprotection sequences (Scheme 12). These oligoarenes are generally highly soluble in common organic solvents when compared with their parent arenes due to the presence of the highly hydrophobic triorganosilyl group.…”

Selective organic synthesis through generation and reactivity control of hyper‐coordinate metal species

“…The major advantage of cross‐coupling with the organosilicon reagents is a ready protection/deprotection maneuver at the hydroxy group, allowing easy iterative cross‐coupling 46. An example is demonstrated by the synthesis of quinquethiophenes.…”

Two-wavelength holographic recording in photopolymer using four-energy-level system: experiments and modeling

“…Holographic Recording Investigations on the previous experimental results [15][16][17][18]20,21 reveal that photosensitive molecules for the TWP holographic recording share a common characteristic: they are α-diketone structure, which can be described by a fourenergy-level absorption scheme with cascaded-excited metastable intermediate levels. An intermediate level of metastable state is essential for this scheme.…”

“…17 More recently, multilayer waveguide holographic memory card was reported in a photopolymer doped with two-colorphotosensitive dye of bis(silyl)pentathiophene and radical photopolymerization initiator of 2,2-dimethoxy-2-phenylacetophenone. 18,19 We recently reported 5% diffraction efficiency from a TWP hologram recorded in a phenanthrenequinonedoped poly(methyl methacrylate) (PQ/PMMA) photopolymer sample of thickness 2 mm by using a UV sensitizing light at 325 nm and red writing light at 647 nm. 20 By adjusting the intensity ratio of sensitizing and writing beams, diffraction efficiency has been increased to >40%.…”