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

Abstract

A light-stabilization mechanism of anionic oxonol dyes for digital versatile disks (DVDs) with 4,4'-bipyridinium cations was analyzed by time-resolved spectroscopy techniques. The analysis showed that for the amorphous solid film of the anionic oxonol dye without 4,4'-bipyridinium cations, the short-lived component with 1.4 ns lifetime and long-lived components with millisecond timescale lifetime were observed: the short-lived component was assigned to the lowest excited singlet state (S1) and the long-lived components were assigned to the lowest excited triplet state (T1) and the metastable photoisomer of the dye. On the other hand, for the amorphous solid film with 4,4'-bipyridinium cations, ultrafast forward (4 ps) and backward (50 ps) electron transfers were observed and the S1 state of the dye was quenched. It was concluded that the observed electron transfer improved the lightfastness of the oxonol dye.