Synthesis, Characterization and Interconversion of p-Tolylsulfone-Functionalized Norbornadiene/Quadricyclane Couples

We report the synthesis and characterization of library of new 2,3-disubstituted norbornadiene/quadricyclane couples. For the first time, the para-tolylsulfone moiety was employed as electron-withdrawing substituent in combination with a variety of different electron donors as counterparts. Comprehensive characterization was conducted for every interconversion couple. By comparison with structurally related molecules published before we established the tosyl moiety as suitable alternative to previously investigated ester functionalities by providing similar photophysical properties. The photo-induced interconversion behavior was investigated via UV/Vis- and NMR-spectroscopy. The UV/Vis experiments were carried out exclusively in acetonitrile, whereas several solvents were investigated in the NMR studies. A detailed description and comparison of the isomerization behavior is provided, while examining relevant optical properties like lambda(max) and lambda(onset). Thereby, an enhanced red-shift up to lambda(max)=394 nm combined with an lambda(onset) value of 469 nm could be generated which is necessary for potential applications.