A new class of light-fast oxonol dyes: organic-glass forming salts of oxonol anions and 4,4′-bipyridinium cations

A Light-Stabilization Mechanism of Anionic Oxonol Dyes for Digital Versatile Disks

“…The reason for the non detection of bleach would be because the absorption of the one-electron reduced form of 4,4 0 -bpy would overlap with the wavelength region, as so presumed in a previous report. 4) To verify this, the absorption spectrum of the one-electron reduced form of 4,4 0 -bpy was measured in accordance with a previous report, 11) and it was confirmed that the one-electron reduced form of 4,4 0 -bpy gave a broad absorption at around 400 to 700 nm. From the above, the transient absorption observed at approximately 450 to 550 nm was assigned to the overlapping of the dye bleach and the one-electron reduced form of 4,4 0 -bpy.…”

“…The typical film thickness was in the 2-3 m range. It should be noted that the lightfastness of the mixed film prepared from the oxonol dye and 4,4 0bpy is somewhat lower than that in the previously reported case 4,10) where a paired salt with the oxonol dye and 4,4 0 -bpy was previously synthesized, but is markedly higher than that of the film prepared from the oxonol dye alone.…”

“…1) were synthesized by previously reported methods. 4,9) Wako special grade 2,2,3,3tetrafluoro-1-propanol was used as solvent for spin-coating. Thin films of the oxonol dye with and without 4,4 0 -bpy were typically prepared as follows.…”

“…3) To enhance the lightfastness of oxonol dyes, electron acceptors that can quench the lowest excited singlet state (S 1 ) of anionic oxonol dyes have been investigated, using 4,4 0bipyridinium dication (4,4 0 -bpy) as a counter cation. 4,5) Introducing 4,4 0 -bpy to the oxonol dye yielded the oxonolsalt dye that is free of heavy metals, soluble, lightfast, and highly suitable for use as an ideal DVD material. 6) From the estimated oxidization potential of the oxonol dye in the S 1 state (À1:17 V vs SCE), the reduction potential of 4,4 0 -bpy (À0:33 V vs SCE), and the decrease in the fluorescence intensity of the oxonol dye with 4,4 0 -bpy, it was speculated that 4,4 0 -bpy quenches the S 1 state of the oxonol dye, 4,7,8) but the evidence and the detailed light-stabilizing mechanism were in doubt.…”

“…4,5) Introducing 4,4 0 -bpy to the oxonol dye yielded the oxonolsalt dye that is free of heavy metals, soluble, lightfast, and highly suitable for use as an ideal DVD material. 6) From the estimated oxidization potential of the oxonol dye in the S 1 state (À1:17 V vs SCE), the reduction potential of 4,4 0 -bpy (À0:33 V vs SCE), and the decrease in the fluorescence intensity of the oxonol dye with 4,4 0 -bpy, it was speculated that 4,4 0 -bpy quenches the S 1 state of the oxonol dye, 4,7,8) but the evidence and the detailed light-stabilizing mechanism were in doubt. In this paper, we report the lightstabilization mechanism of the oxonol dye for DVDs with 4,4 0 -bpy analyzed by a time-resolved spectroscopy technique.…”