A series of photochromic bisthienylethenes (BTE) chromophores with different central ethene bridges were synthesized. Up to date, the rational design of BTE have been mainly carried out on the side aryl groups. In our work, the influence of the aromaticity of the central ethene bridge on the photochromic properties was studied. Moreover, unlike in the literature where most of BTE have a five-membered ring bridge, six-membered ring bridges were used. In Chapter 1, examples of photochromes are given, along with the main definitions. Chapter 2 deals with BTTE, a BTE with a benzobisthiadiazole bridge and with excellent photochromic properties. c-BTTE, the closed isomer, exhibits excellent thermal stability in various solvents and in the solid state. Its fluorescence can be modulated by solvato- and photochromism. It eliminates the usual bias of thermal back reaction, typical of BTE with a six-membered ring ethene bridge. Chapter 3 is devoted to compounds with bridges having different aromaticities (BTE-NA, BTA and BTTA). Their fluorescence can be modulated by solvato- and photochromism. The relation between aromaticity and thermal stability was established: the low aromaticity of the central ethene bridge with benzobisthiadiazole unit leads to a thermal irreversibility for BTTA, and the small energy barrier between the parallel and anti-parallel conformers and the great difference in absorption between BTTA and c-BTTA allow the full conversion from BTTA to c-BTTA. Molecules with a benzothiadiazole bridge, designed for complexation and for switchable nonlinear optical properties were prepared (Chapters 4 and 5). However, the targeted properties were not evidenced up to now.
