NOVEL PHOTOCHROMIC 2H-CHROMENES WITH PI-DONOR SUBSTITUENTS IN THE 2H-PYRAN RING

A series of novel photochromic 2H-chromenes containing the ethynyl or ethoxy groups in position 4 (I, IT) and an annelated pyrrole ring(IPP, IV) have been synthesized and their spectral and photochromic properti es studied. The chromenes I-IV are characterized by high rates of ther mal bleaching reaction in liquid solutions at room temperature. Longwa ve absorption bands of the chromenes I have their maxima at 295-308 nm , whereas their photoisomers absorb at lambda(max)=437 nm (glassy isop entane-isopropanol, 4:1 solvent, T<200 K). For the type chromenes III, IV the longwave absorption bands are found in the regions of lambda(ma x)=323-325nm (ring-closed form A) and lambda(max)=675-678nm (ring-open ed form B).