Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.297, 213-218, 1997
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 properties studied. The chromenes I-IV are characterized by high rates of thermal bleaching reaction in liquid solutions at room temperature. Longwave absorption bands of the chromenes I have their maxima at 295-308 nm, whereas their photoisomers absorb at lambda(max)=437 nm (glassy isopentane-isopropanol, 4:1 solvent, T<200 K). For the type chromenes III,IV the longwave absorption bands are found in the regions of lambda(max)=323-325nm (ring-closed form A) and lambda(max)=675-678nm (ring-opened form B).