Synthesis and photochromic properties of N 2-alkyl-5-furyl-4-thienylpyridazinones

New dihetarylethenes containing the six-membered bridging moiety, viz., N ²-alkyl-5-furyl-4-thienylpyridazinones, were synthesized. These compounds have photochromic properties in solution. The hindered rotation of the thiophene and furan rings around the single bonds that link these rings to the double bond of the pyridazinone moiety results in the formation of mixtures of chiral diastereomers in solution, the lifetimes of the diastereomers being no longer than 0.2 s. The photochromic rearrangement of pyridazinones is characterized by the highly efficient photocoloration and the photobleaching, which is an order of magnitude less efficient, in the absence of thermal relaxation processes.