Abstract:
Photochromic compounds are the paradigm of organic functional materials.1 These so-called photoswitches undergo a photoinduced reversible transformation between two forms with different absorption. Such photochromic compounds may reversibly change their structure as well as their
chemical and physical properties,2, so that they are applied in light-responsive materials, such as, for example, self-coloring sunglasses,3 photomechanical crystals,4 energy storage systems (molecular solar thermal, MOST),5 or even photopharmaceuticals.6 In this presentation, two representative applications of photochromic compounds will be presented.
In the first part, concepts to accomplish a photo-induced complexation of photoactive substrates with DNA will be discussed with emphasis on the trade-off between appropriate photochromic properties and sufficient affinity of the ligand unit towards the DNA. Specifically, the reversible photocycloaddition reactions of styrylquinolizinium and benzo[b]quinolizinium (azoniaanthracene) derivatives to generate DNA ligands upon irradiation will be discussed.7
In the second part, the optimization of the intramolecular [2+2] photocycloaddition/cycloreversion of norbornadienes/quadricyclanes for an application in molecular solar thermal energy storage (MOST) will be presented. Specifically, it will be demonstrated that monoarylnorbornadienes exhibit favorable photochemical and physico-chemical properties for the conversion of light energy in storable chemical energy and controlled release thereof.8 Most notably, both cycloaddition and cycloreversion can be accomplished by irradiation with light in the visible range with a well-balanced combination of substitution paWern of the arylnorbornadiene and suitable photocatalysts.