Rewritable Near-Field Optical Recording on Photochromic Perinaphthothioindigo Thin Films: Readout by Fluorescence

Abstract

Near-field optical recording on polystyrene thin films containing photochromic perinaphthothioindigo (NTI) was carried out. NTI underwent a reversible trans/cis photoisomerization in the polystyrene film, and only the trans-form emitted fluorescence. First, polystyrene film containing trans-form NTI molecules was used as the recording medium. Upon irradiation with 633 nm light from a fiber probe tip (aperture diameter ∼100 nm), the fluorescent trans-forms in a small region were converted into nonfluorescent cis-forms. The recorded small regions were detected as dark spots as small as 110 nm by scanning across the written area. Second, polystyrene film containing cis-form NTI molecules was used as the recording medium. Upon irradiation with ultrasmall 488 nm light (aperture diameter ∼80 nm), bright spots as small as 50 nm were recorded and read out with scanning 633 nm light. The bright spots were due to the fluorescence of the photogenerated trans-form NTI molecules. Both the dark and bright spots were erased by irradiation with 488 nm and 633 nm light, respectively. The bright spot could also be recorded using a pulse Nd 3+ : YAG laser (532 nm, pulse width 20 ns).

Two-Photon Absorbing Molecules as Potential Materials for 3D Optical Memory

“…Therefore, usual photochromic compounds, such as azobenzenes and diarylethenes, cannot be used for porphyrin. However, the S 1 state of the trans-isomer of perinaphthothioindigo PNT (2.0 eV) [55] is lower than that of zincporphyrin. The trans-isomer of 13 exhibited a strong Soret band at 435 nm and a broad absorption at 655 nm originated from porphyrin and trans-PNT, respectively.…”

Synthesis and photophysical properties of a porphyrin-perinaphthothioindigo dye

“…Therefore, usual photochromic compounds such as azobenzenes and diarylethenes cannot be used in this system. However, since the S 1 state of the transisomer of perinaphthothioindigo (PNT, 2.0 eV) [14,15] is lower than that of zinc porphyrin, isomerization of the PNT part is expected after two-photon excitation of the zinc porphyrin moiety [16]. In this way, at first, we designed a PNT attached-bisporphyrins 2 using an ethynylene bond as a more efficient two-photon absorbing photochromic compound as shown in Scheme 1.…”

Synthesis and optical properties of photochromic perinaphthothioindigo

“…Furthermore, their fluorescence may be excited in the red, where inexpensive diode lasers are available. The photoswitching of bis(perinaphtho)thioindigo has been previously suggested for optical data storage and imaging [3,4].…”

“…Thus, even with monochromatic light incident on the sample at the maximum absorption of either form, only photostationary states containing a mixture of the two isomers could be prepared. Perinaphthothioindigo dyes have been reported by several groups [3][4][5][6][7][8][9][10]; the absorption spectra and properties differ among the dyes. Little information is available in the literature regarding synthesis of the perinaphthothioindigos: typically reference is made to a paper by HarleyMason and Mann [11], which does not provide specific details on this synthesis.…”

“…(B) The perinaphthothioindigo studied here, PNT, cis form. (C) The perinaphthothioindigo studied in Refs [3,4,6]. referred to as NTI.…”