Monitoring changes in ultraviolet-visible (UV-vis) absorption is not a viable method to process information for photochromic memory media due to the readout signal interfering with the photochromism. Only by monitoring the changes in other photophysical properties accompanying the photoisomerization reaction (refractive index, optical rotation, or luminescence, for example) can non-destructive, all photon-mode photochromic memory be realized. We have investigated several such systems based on 1,2-dithienylcyclopentene derivatives, which have a backbone that we consider to be currently the most promising of the photochromes. The two readout signals highlighted in this article are luminescence and optical rotation. The luminescent systems rely on porphyrinic chromophores tethered to the photochrome directly or through dative bonds. When the macrocycles are irradiated with light at wavelengths outside the absorption range of the photochrome, luminescence is only observed when the 1,2-dithienylcyclopentene backbone exists in its open-state. The self-assembly of a chiral photochromic metallo-helicate allows for stereoselective ring-closing of the 1,2-dithienylcyclopentene backbone providing a change in optical rotation that can be used as a readout signal. In the article, we also describe the use of ring-opening metathesis polymerization (ROMP) to fabricate well-ordered photochromic homopolymers possessing identical photochromic properties as their monomers.
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