PHOTOINDUCED PROTON TRANSFER IN MACROMOLECULAR SYSTEMS

Photochromic materials are well known candidates for several technological applications such as devices for the optical storage of informations, optical switches and in general as materials exhibiting photoresponsive properties when irradiated with light of suitable frequency and intensity. In particular in the last few years a great interest grew up on using these compounds as building blocks for the construction of molecular logic gates able to perform simple logic operations (AND, NOT and OR). These molecular switches are based on the interplay between chemical, electrical or optical stimulations and absorbance, luminescence or redox outputs In this regard, spiropyran (SP), a three state molecular switch, has been widely studied and resulted promising for obtaining a device able to elaborate information by detecting inputs of one form and transducing them into outputs of another one1. As previously reported [6-8], irradiation of this colourless compound with UV light induces heterolytic cleavage of the spiro carbon-oxygen bond, thus producing the ring opened and intensively coloured merocyanine form (ME). This process is thermically and photochemically reversible. Furthermore the addition of acid induces the formation of the protonated merocyanine MEH which, if irradiated with Visible light, releases a proton and comes back to SP. The absorption and emission properties of these three states (SP, ME and MEH) are significantly different and allow to use these compounds for repeated data recording and optical data storage.