Reversible Photodimerization: a New Type of Photochromism

Abstract

The photodimers formed by polycyclic aromatic hydrocarbons, such as anthracene, and their derivatives can be photodissociated to the original monomers. When the photodimer is held in a rigid matrix, the dimer can be remade efficiently because the two monomers are held in the proper relationship for photodimerization. The absorption spectra of monomer and photodimer differ substantially, and associated with this is a difference in refractive index. These characteristics as well as the stability of both states at room temperature make such a system attractive for reversible phase holographic recording with nondestructive readout. We have investigated several photodimer systems as solutions in rigid transparent polymer matrices, as well as some single crystals of photodimers. We have been able to write and erase diffraction gratings repeatedly. The photosensitivities ( 0.1 J cm(-2)), which are close to the maximum possible for a system with no gain, are high enough to be useful. Grating scattering efficiencies in the range of 0.01-5% have been observed. The physical, chemical, and photochemical characteristics of these systems, as well as some basic general considerations, are discussed.

Photostability of dye molecules trapped in solid matrices

“…[9][10][11][12][13][14] Different physical mechanisms are possible. We present a simple theoretical model based on a one-photon process in which each dye molecule has a certain probability of being transformed into a bleached molecule after having absorbed a certain number of photons.…”

Photochromic Polymers for Optical Data Storage: Azobenzenes and Photodimers

“…In the case of oligopeptides, an ornithine-glycine hexamer gave a maximum transmission of 68% in 1500 s for an intensity of 30 mW cm À2 . An estimation of the absorption cross-section for photons based on the theory developed by Tomlinson et al [59] gave a value of 9 Â 10 À20 cm 2 far below the theoretical maximum of 1.2 Â 10 À18 cm 2 [65]. The reason being that a peptide backbone was too rigid to permit a molecular adjustment.…”

“…Tomlinson et al [59,60] investigated cycloaddition reactions in organic materials for holographic storage of information. A cycloaddition reaction is a ring-forming addition of m atoms of one group to n atoms of another group.…”

Large Photoinduced Refractive Index Changes of Transparent Polymer Films Containing Photoeliminable Diazo and Azido Groups

“…Photoisomerization is a reversible one and is applicable to write-readerase (WRE) recordings and switching devices. [1][2][3][4][5][6][7] Typical compounds used for photoisomerization are azobenzene, spirobenzopyran, and diarylethene derivatives. Photopolymerization, photolocking, and photoelimination are irreversible reactions, and can be used for readonly holographic memories, waveguide lithography, microlenses, and other optical elements.…”