Département de chimie moléculaire

A series of photochromic derivs. based on the trans-10b,10c-dimethyl-10b,10c-dihydropyrene (DHP, "closed form") skeleton was synthesized and their photoisomerization leading to the corresponding cyclophanediene (CPD, "open form") isomers was studied by UV/Vis and 1H NMR spectroscopies. Substitution of the DHP core with electron-withdrawing pyridinium groups was found to have major effects on the photoisomerization efficiency, the most remarkable examples being to enhance the quantum yield of the opening reaction and to allow fast and quant. conversions at much lower radiant energies. This effect was rationalized by theor. calcns. We also show that the reverse reaction, i.e., going from the open form to the closed form, can be electrochem. triggered by oxidn. of the CPD unit and that the photo-opening properties of pyridine-substituted DHPs can be efficiently tuned by protonation, the system behaving as a multi-addressable mol. switch. These multi-addressable photochromes show promise for the development of responsive materials. [on SciFinder(R)]