Photochemical Hole Burning of Porphin-Cross-Linked Polymers

It is well known that porphin derivatives such as tetraphenylporphin (TPP) molecularly dispersed in organic polymers such as polymethylmethacrylate (PMMA) exhibit photochemical hole burning (PHB). In this kind of porphin/polymer system of simple dispersion type, large irreversible broadening of photochemical holes is observed even at extremely low temperatures around liquid helium temperature [1]. This broadening, or spectral diffusion, is caused by the energy shift of the electronic states of the porphin molecule brought about by the structural changes which take place in the organic amorphous polymer. The reduction of this spectral diffusion is one of the main subjects for the possible application of PHB to high-density optical memory. In the previous paper [1], we reported on the spectral diffusion in the copolymer of methylmethacrylate (MMA) and TPP derivative with four functional groups and showed that the spectral diffusion is suppressed by the covalent bonds formed between TPP and the host polymer. Besides, we reported that the hydrogen bonds formed in the host polymer also suppress the spectral diffusion, which was confirmed for the several porphin derivatives with ionic substituents dispersed in polyvinylalcohol (PVA), one of the most efficient hydrogen bonding polymers [2]. Then, we may expect still less spectral diffusion in such materials that have both the covalent bonds between TPP and the host polymer, and the hydrogen bonds in the latter. In this study, we will show that this anticipation is true.